17. Display and Illumination of Color and B&W Prints

50 Pages·2013·1.63 MB·English

575 The Permanence and Care of Color Photographs Chapter 17
17. Display and Illumination of Color and B&W Prints
The Alarming Light-Induced Image Discoloration and
Base Cracking of B&W RC Prints on Long-Term Display
Those serving the needs of collections being as for how much image fading and staining can be toler-
heavily used for exhibition face a serious di- ated. As discussed in Chapter 7, valuable color prints should
lemma. On one hand, they are chronicling, aid- be monitored with a densitometer, and visually significant
ing and abetting in the systematic destruction changes in color balance, overall density, and minimum
of the photographs they are charged to protect density stain levels should not be permitted to take place. >
by supporting reprehensible exhibition prac- Display of color prints is inherently detrimental to them, pdf
tices. On the other hand, they largely owe their but avoiding display runs counter to the reasons most pho- _v1.
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existence to those very exhibition programs. tographs are made and frequently conflicts with the pur- e
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. . . The current exhibition vogue amounts to poses for which most individuals and museums collect prints. _Hi
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a systematic program of accelerating the deg- _2
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radation of our most valued and important pho- The Expendable or Replaceable Color Print 7_
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tographs. The practice can and must be changed. k_
No doubt there will be many who will claim that If a color print has no lasting value — or if it can be Boo
such an assessment is too extreme and that replaced with a new print after the original has deterio- W_
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tshaey tphraotb wleem d ois nboeti hnagv eex eangoguegrhat iendf.o r mThaetiyo nw tilol rthaoteudg h— th iety cmanay b bee dexisppelnaysievde twoi trheopulat cme,u dcehc ocraautitvioen p. r inAtls- me: <
change our ways. I would say we do not have and murals of the types found in many corporate offices e na
enough information to maintain them.1 and in public places such as hotel lobbies, restaurants, and er fil
airports are usually expendable. Museums, however, do nd
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Grant B. Romer, Conservator not generally consider their prints to be expendable, even 3
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International Museum of Photography if a faded print could be replaced during a photographer’s 20
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at George Eastman House lifetime. e
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Rochester, New York – September 1986 In some instances it might be possible to obtain re- n Ju
placement color prints for faded baby pictures, high school > o
portraits, wedding photographs, and family portraits from m
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Introduction the photographer who took them. Many professional pho- h.
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tographers, however, keep negatives for only a relatively ar
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andP hino taong reaxpthrse mareely d wisipdlea yreadn gfoer o mf laignhy tdinifgf ecroenndt itrieoansso n—s sthhaotr tr etiomrdee —rs omftiegnh ot ncloym foer i ans. lMonogs ta so fe txhpee rloiewn-cceo sint d“micaatsess- elm-res
see Table 17.1. Whereas modern fiber-base black-and-white market” portrait operations — such as those that travel wilh
prints that have been correctly processed and treated with from department store to department store, taking photo- ww.
a protective toner are extremely stable and may be ex- graphs only a few days at each location — dispose of their <w
pected to have a very long life under typical conditions of color negatives almost immediately after the selection of d at
display,2 the same cannot be said for most kinds of color prints is made; the cost of filing and storing negatives is ate
yplreinntes-,r eosri nfo-rc obalatecdk)- apnadp-ewrhsi.te prints made on RC (polyeth- proEhvibeinti vief afo rp hthoetoseg rloawph-oevre drhoeeas dk, eheigph c-voololur mnee gbautsivineess, stehse. nt origin
With the singular exception of color pigment prints made negatives may be too faded to make satisfactory prints me
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with the new UltraStable Permanent Color process and after years have passed. This is especially true if the pho- oc
the Polaroid Permanent-Color process,3 exposure of color tographs were made on earlier, low-stability films such as his d
photographs to light during display will cause slow but Kodak Kodacolor II, Vericolor II, and Process E-1, E-2, and T
inexorable fading and staining of the image; visible light E-3 Ektachrome films.
and ultraviolet (UV) radiation may also cause cracking and
other physical deterioration of the print emulsion and sup-
Display of Nonreplaceable Color Prints
port material. This does not mean that color prints cannot
or should not be displayed, but if such photographs are to When it is desired to keep a color print in good condition
be preserved for long periods of time, the stability charac- for as long as possible, there are limitations on how long
teristics (including fading rate) of the color print material the print can be exposed to light on display. Guidelines for
must be understood. The planned total time of display the display times of current and many older color print
must be determined with consideration for the intensity materials are given in Chapter 3. As a general rule, it may
and spectral composition of the illumination source as well be assumed that under typical moderate display condi-
tions, the light fading rate of a given type of color print is
approximately proportional to the light intensity on the
See page 577 for Recommendations
print. For example, a print displayed for 12 hours a day in
Display and Illumination of Color and Black-and-White Prints Chapter 17 576
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1982 under fil
May 2003
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The 1982 exhibition Color as Form: A History of Color Photography at the Corcoran Gallery of Art in Washington, D.C. un
The display area was illuminated with incandescent tungsten lamps with an average intensity of about 170 lux. The first n J
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major survey of color photography as an art form, this show was curated by John Upton for the International Museum of >
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Photography at George Eastman House in Rochester, New York. The exhibition opened at the Corcoran for 3 months and o
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was later shown at George Eastman House. With vintage prints made by a wide variety of color processes — most with ch.
unknown stability characteristics — this was the first photography exhibition to be densitometrically monitored for image ear
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fading and staining. m-re
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1,000 lux of light will fade at about twice the rate of a print replacing most of the photographs in its regular exhibition wilh
displayed the same amount of time in 500 lux. Because the areas with other photographs from the collection so that w.
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human eye has a great ability to adapt to different light no print is on constant display. w
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intensities, a person is often not aware of the great range When purchasing a color print, it may be possible to at
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of light intensities that usually exist in a room, or in differ- obtain a duplicate copy at low cost; one print can be dis- ate
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ent parts of a building. In museum display of original color played with the realization that it will fade over time, while gi
photographs, densitometric limits of tolerable color fading the other can be kept in the dark for preservation pur- nt ori
should be established and a monitoring program instituted poses. When the displayed print has faded to the point me
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to make certain that prints are not permitted to fade or where it is no longer acceptable, a copy print for display oc
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stain beyond those limits (see Chapter 7). can be made from the stored print; the one remaining original s
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Some museums have guidelines for exhibition of color print should continue to be kept in the dark under the most T
and black-and-white photographs which apply to works both favorable conditions possible. For persons making their
in the museum and out on loan. The Museum of Fine Arts own color prints, it is a simple matter to produce one or
in Boston permits a maximum display time of 3 months two extra prints for display purposes. In recent years the
every 2 or 3 years; if a print has been exhibited in the Art Institute of Chicago has attempted to obtain duplicate
previous year, the museum will not send it out on loan. prints of the color photographs acquired for its collection
The Metropolitan Museum of Art in New York City has a so that one print can be used for exhibition and study pur-
policy of displaying color photographs no more than 3 or 4 poses and the other kept in the dark in the museum’s hu-
months every 5 to 10 years. In the past, the International midity-controlled cold storage facility. The Museum of
Museum of Photography at George Eastman House kept a Modern Art in New York City also attempts to obtain two
number of its better-known photographs on permanent copies of each of its chromogenic color print acquisitions;
display; some of the museum’s traveling exhibitions were one copy is kept in permanent storage in a frost-free refrig-
out on loan to a succession of institutions for years at a erator, and the other is withdrawn from the refrigerator
time. More recently, the museum has been periodically when needed for study or exhibition purposes.
(continued on page 578)
577 The Permanence and Care of Color Photographs Chapter 17
Recommendations
Display of Color Prints
(see Chapter 7). It is recommended that salted paper prints
* Nonreplaceable color prints. Unfortunately, with the
(ca. 1840–1855) and albumen prints (ca. 1850–1895) never
exception of UltraStable Permanent Color and Polaroid
be displayed — not even for short periods.
Permanent-Color pigment prints, almost all other types
of color photographs exposed to light on display slowly Glass and UV-Absorbing Framing Materials
fade over time and will eventually become severely
* UV filters do little to protect most color prints. With
degraded. Valuable or nonreplaceable color prints should
Ektacolor, Fujicolor, Konica Color, Agfacolor, and most other
never be subjected to prolonged display. The light
current color print materials displayed in typical indoor con-
fading stability of different types of color prints varies
ditions, image fading is caused primarily by visible light, not
over a wide range, with some color prints lasting far
by ultraviolet radiation. Ultraviolet filters such as Plexiglas
longer than others under the same display conditions
UF-3 do little if anything to increase the life of these color
(see Chapter 3). Only expendable color prints having
materials, largely because they are manufactured with an
no lasting value, or those for which duplicates are be- >
effective UV-absorbing emulsion overcoat. One exception is df
itnhgat kreepplta icne dmaernk ts ptroinratsg ec,a no rb teh mosaed feo irn w thheic fhu tiut ries, csehrotualidn Ilford Ilfochrome print materials (called Cibachrome 1963– _v1.p
be subjected to prolonged or “permanent” display. 1991), which are manufactured without a UV-absorbing over- Res
coat. When Ilfochrome prints are displayed under direct or Hi
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Illumination Levels indirect daylight, framing with a UV filter markedly increases _20
their stability. The improvement is much less for prints illumi- of
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* For museums, galleries, and archives. Approxi- nated with fluorescent or tungsten light (see Chapter 3). 17
_
mately 300 lux of incandescent tungsten or glass-fil- ok
tered quartz halogen illumination is recommended. This * Glass is recommended over Plexiglas and other plas- Bo
author believes that light levels below 300 lux are insuf- tics for most framing applications. Glass is inexpensive, HW_
fpicairetinctu lfaorrl yp rcooploerr pvhisoutaolg arappphrse.c i aPtiroinnt so fs hpohuoltdo gbrea pdhiss-, ehaoswye vtoer ,c iut t,s hcohuelmd incaoltl yb ein uesrte, da fnodr trreasviestlianngt etox hsibcirtaiotcnhse osr; me: <
played with adequate illumination. There is no “mini- for very large prints where breakage could occur. For these e na
mdouems ”n iolltu omcincuarti.o nA clecvueml ualta twedh icdhis pcloalyo rt imprein mt ufasdt inbge aDpispplilcaaytiinogn sp,r isnttasn fdraamrde dc lewaitrh P glelaxsigs laosr PGle ixsi grleacso Gm madejnadceednt. nder fil
limited to prevent excessive fading. Modern black-and- to prints framed with Plexiglas UF-3 can be visually distract- 3 u
white fiber-base prints may be displayed at significantly ing. The light-yellow tint of UF-3 gives white mount boards 200
higher illumination levels (e.g., 600 lux or higher) as and low-density areas of photographs a distinctly yellowish, e 6,
or warm, appearance; prints framed with glass look dis- n
long as the surface temperature of the prints in black u
(d-max) areas does not increase more than a few de- tinctly different. Furthermore, UF-3 suppresses the effects of on J
grees. Heating of prints reduces emulsion and base fluorescent brighteners that are incorporated in virtually all m>
moisture content, which may in turn cause increased current black-and-white papers; this has the effect of subtly co
dulling the appearance of the prints. Even with incandes- h.
curl and/or eventual cracking, especially in RC prints. c
cent tungsten illumination, which has very low UV content, ear
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* mFoarte hlyo 4m5e0 launxd o fc ionmcamndeercsciaeln ta ptupnlgicsatetino, ngsla. s sA-pfilpterorexdi- the dulling effect of UF-3 is noticeable. elm-re
quartz halogen, or glass-filtered fluorescent illumina- Black-and-White RC and Fiber-Base Prints wilh
tion is recommended. In many commercial display * Double-weight, fiber-base papers are strongly recom- ww.
situations, bright ambient lighting conditions will re- mended. Current information indicates that fiber-base prints <w
quire significantly higher illumination levels to show are, overall, substantially more stable than RC prints, espe- at
photographs to their best advantage. cially when displayed for prolonged periods. Fiber-base ated
* Museums and photographers should adopt a stan- pimriangtse adlissoc oalpopraetaior nt oc abues eleds sb ys ussucrfeapcteib cleo nthtaamn inRaCn ptsr,i nptoso tro- origin
sdhaordul di lalucmcuinraatteiloyn c olenvveeyl. th eA spuhbotlteotgiersa pehn voisni odniesdp lbayy quality storage materials, and/or commonly encountered ment
the photographer. To accomplish this, it is essential levels of air pollutants. Many RC prints made with devel- ocu
oper-incorporated papers (e.g., the now-obsolete Ilford Mul- d
that the print be evaluated for density and color balance s
tigrade II RC paper) have, after only a few years of storage, hi
in the darkroom under the same intensity and type of T
developed serious brownish stain within the paper base
illumination with which it will be displayed in a gallery
itself. RC papers should not be used for historically impor-
or museum. It is proposed that galleries, museums,
tant photographs, fine art prints, or portraits. Fiber-base
and archives formally adopt the above-recommended
prints intended for long-term display or storage should be
300 lux of incandescent tungsten or glass-filtered quartz
treated with an image-protective toner (see text). This au-
halogen illumination against a light, neutral background
thor considers treatment with a protective toner to be an
and that photographers be encouraged to use this illu-
essential part of “archival” processing. Virtually all modern
mination condition for evaluating prints.
black-and-white papers are made with fluorescent brighten-
* Museums and archives should monitor prints. Den- ers, which gradually lose activity (“fade”) when displayed.
sities at selected image locations on color and black- Thus, although the image and base of an “archivally” pro-
and-white prints should be measured periodically with cessed fiber-base print are extremely stable, the loss of
an accurate electronic densitometer, and predetermined brightener effect will cause the whites and highlights of the
limits of fading and staining should not be exceeded print to lose some of their original brilliance.
Display and Illumination of Color and Black-and-White Prints Chapter 17 578
Instant color photographs, none of which have usable
negatives for making new prints, are in most cases not
replaceable. In addition, all current Polaroid and Fuji in-
* Display of black-and-white RC prints. Valuable black- stant color prints have relatively poor light fading stability;
and-white RC prints should never be displayed. Espe- valuable instant prints should be displayed for short peri-
cially when framed under glass or plastic and displayed ods only.
for prolonged periods, even at low light levels with UV-
filtered illumination, black-and-white RC prints may be
Display of Black-and-White RC Prints:
subject to light-induced oxidation of the silver image,
Caution Is Necessary
resulting in ugly yellowish or orange-red image discol-
orations. Black-and-white RC prints are also subject to Black-and-white RC (polyethylene-resin-coated) papers
base and/or emulsion cracking as a result of display.
first became generally available in the United States with
* Kodak B&W RC papers are recommended. If it is the introduction of Kodak Polycontrast Rapid RC Paper in
decided to use an RC paper, then Kodak Polymax RC October 1972.4 RC papers made by Ilford (Ilfospeed and
Paper and Polyprint RC Paper, both conventional-emul- Ilford Multigrade papers), Agfa-Gevaert (Brovira PE df>
sion (non-developer-incorporated) papers, currently are Paper, later called Brovira-Speed Paper), and other manu- 1.p
recommended. There are substantial differences in facturers worldwide soon followed. RC papers now consti- s_v
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image and base stability of black-and-white RC papers. tute the great majority of all black-and-white photographic HiR
At the time of this writing, Kodak was the only manufac- _
papers produced. Use of fiber-base papers increasingly 0
turer that had published meaningful accelerated aging _2
is limited to fine art photographers, advanced darkroom of
projections for its RC papers with respect to base crack- hobbyists, and top-quality advertising and commercial 17_
ing, and Kodak also has described the stability benefits k_
photographers (advertising photographers prefer the su- o
afforded by its “stabilizer in the paper core” technology. o
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Until meaningful comparative accelerated aging data perior retouching and knife-etching capabilities of fiber- W_
are available on the base and image stability character- base papers). <H
istics of the RC papers supplied by other manufactur- Whether because of an appreciation of the superior sur- me:
ers, Kodak RC papers will continue to be recommended. face and image qualities afforded by the best fiber-base na
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Imt eisth roedcso gonfi zderdy,i nhgo wReCv eprr,i nthtsa,t twhieth i mthaeg em oasntd c osumrmfaocne puanpperorsv,e no rm paetrehraiapls, fibneec aaurts ep hoof toag rrealpuhcetrasn cine tthoe aUd.oSp. ta nand der fil
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quality of most RC papers, including Kodak, may prove most other countries have — fortunately — thus far almost 3 u
visually unacceptable because of “veiling” of the blacks completely avoided black-and-white RC papers in making 200
(see below). Should this be the case, Oriental New prints for exhibition or sale. e 6,
Seagull Select VC-RP, a variable-contrast paper, and n
Oriental New Seagull RP, a graded paper, both of which ethRylCe npea poenr ibso mtha sdied ebsy hofo ta-e fxitbreurd-binags ea pthaipne lra yceorr eo;f cploelayr- on Ju
give good results even when dried at room tempera- >
polyethylene is coated on the back of the print (often the m
ture, are probably the only satisfactory alternatives. o
paper core is first printed with the manufacturer’s name in h.c
* Ilford RC print processors and dryers are recom- light gray ink) and polyethylene pigmented with white tita- arc
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mgloesnsd, eadn.d tThhee o vdeerpatlhl v oisfu tahl eim balgacek qsu, atlhitey opfr iKnot dsaukr faancde hniiguhm- rdefiloexcitdaen c(Te ipOi2g)m ies nctoeadt leady eorn s ethrvee es mthuel ssiaomn es igdeen; etrhael m-res
mdeogsrta odtehde rw bhleanck t-haen dp-rwinhtiste a RreC dpraiepde rast arroeo smig nteifmicpaenrtaly- fsuunscpteionnd eads i nth gee lbaatrinyt)a i nl afiybeerr -(bcaosmep porsiendts o. fT bhaer ieummu lssuiolfna ties w.wilhel
tsuurceh o ar sd rtiheed dwriythe rc oinn vtheen tiKoondaal kh oRt-oayira lRpCri npt ripnrto dcreysesrosr, cthoea teemd uolns itoonp aocfc tehses ipbilgem toe ndteevde plooplyeer tahnydle onteh elary perro, cleeasvsiinngg at <ww
(discontinued in 1991). For best results, RC prints should d
be dried with one of the Ilford infrared print dryers. The solutions. ate
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sratatendd -inal othnee I lIflofordrd 2 214205 0a nddr y2e1r5 a0n RdC tphrei ndt rpyreorcse isnscoorrsp aol-l porBt eecsasuenseti athlley pwoaltyeertphryoleonf, ev elaryye frass tr epnrodceer stshien gp,a wpaesrh siunpg-, nt origi
provide excellent results. Also satisfactory is the Kodak and drying of RC prints are possible. With an automatic me
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Polymax IR processor; introduced in 1991, this is the processing machine, an RC print can be developed, fixed, oc
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first Kodak processor to be equipped with an infrared washed, and dried in as little as 55 seconds; manual pro- s
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dryer. Unlike the case with RC prints, the images on cessing, including washing in trays and drying with an electric T
fiber-base papers are not noticeably affected by the hair dryer, typically takes 8 or 10 minutes. To correctly
method of drying; fiber-base prints can be dried emul-
process, wash, and dry double-weight fiber-base prints, on
sion-side down on clean, plastic-coated fiberglass screens
the other hand, requires a minimum of about an hour. When
at room temperature with outstanding results.
processing fiber-base prints for maximum permanence, with
* Valuable RC prints should be treated with an im- air-drying on plastic-coated fiberglass screens at room tem-
age-protective toner. Especially if they are to be dis- perature — what is often called “archival processing” —
played, valuable black-and-white RC prints should be the total time can extend to as long as 12 hours. Speed of
treated with Kodak Poly-Toner or Kodak Rapid Sele- processing is the primary appeal of RC papers and is the
nium Toner to help protect the silver image against the
principal reason they were invented. And unlike fiber-base
peculiar types of discoloration (oxidation) to which RC
prints, RC papers have little tendency to curl, even in envi-
prints are susceptible. Toner treatment will not, how-
ronments with low or fluctuating humidity .
ever, increase the resistance of RC papers to cracking.
RC papers should not be confused with print materials
coated on ICI Melinex 990, a high gloss, opaque white poly-
579 The Permanence and Care of Color Photographs Chapter 17
ester sheet manufactured by Imperial Chemical Industries weight fiber-base paper, and after considerable experimen-
(through a complex manufacturing process which forms tation, the company found it in polyethylene-coated paper.
billions of microscopic “voids” of high refractive index within An important reason that polyethylene was chosen for this
the polyester structure of Melinex 990, a bright white ma- application is that it is the least expensive of all plastics —
terial is produced without the need for an added pigment which is why it is also the material of choice for garbage
such as titanium dioxide). Among current products coated bags, plastic milk bottles, and many other inexpensive dis-
on Melinex 990 (or other closely related high gloss, opaque posable consumer items.
white polyester support) are Ilford Ilfochrome glossy print
materials (semi-gloss Ilfochrome is an RC paper), and spe-
Deterioration of Displayed RC Prints
cial-purpose products such as Fujiflex SFA3 Super-Gloss
Printing Material, Fujichrome Printing Material, Kodak Many framed black-and-white prints made on Kodak
Duraflex RA Print Material, Konica Color QA Super Glossy Polycontrast Rapid RC Paper and Ilford Ilfospeed [RC]
Print Material Type A3, and Agfachrome 410 high gloss Paper manufactured in the 1970’s and early 1980’s have,
polyester color print material for transparencies. during the course of only a few years of display under
UltraStable Permanent Color prints and Polaroid Per- normal conditions, suffered catastrophic, irregular gold- >
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manent-Color prints are also made on an opaque white poly- like, orange-red, or yellow image discolorations (sometimes 1.p
ester support; the surface gloss of these prints can vary called “bronzing”) and have developed localized “silver s_v
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from a semi-gloss to a fairly high gloss, depending on the mirror” deposits on the emulsion surface in high-density HiR
formulation of the gelatin used to overcoat the image lay- areas of the image. Sometimes these discolorations are 0_
2
ers after they have been affixed to the polyester support. accompanied by large numbers of small, bright orange-red of_
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Solid polyester supports are more expensive — but tougher spots, identical in structure to the microspots (also known 17
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and far more stable during aging — than RC paper sup- as “redox blemishes” or “microscopic blemishes”) that in ok
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ports. Prints made on Melinex 990 have a mirror-like gloss the past have been found principally on stored microfilms _B
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that is much smoother and glossier than the highest gloss and astronomical plates. Microspots are also occasionally H
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surface that can be produced on an RC paper. One draw- encountered on conventional camera and motion picture e:
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back of Melinex 990, however, is that it cannot readily be films, glass-plate negatives, and glass lantern slides. But, a
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mgloasnsu fsaucrtfuarceed s wimitihla ort htoe rt hthe apno pa uhliagrh K golodsask s Nu rsfuacrfea. c Ae sise mnoit- ttoyp teh eh abvees tn eovfe trh bise eanu tfhouorn’ds oknn ofiwbleerd-bgae,s em picrrinotssp.ots of this der file
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available and this, along with the higher cost of polyester The Corcoran Gallery of Art in Washington, D.C., the 3 u
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materials, has restricted their use in portrait, wedding, fine Art Institute of Chicago, and the National Archives of Canada 0
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art, and most other areas of photography where photogra- in Ottawa are among the well-known institutions that have e 6,
phers generally prefer semi-gloss or matte surface papers. deteriorated black-and-white RC prints in their collections. un
With the exception of a few special-purpose products, These prints became severely discolored after only a few on J
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black-and-white papers are not presently supplied on poly- years of display and storage; with the passage of time, it is m
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ester supports. This is unfortunate, because if such a print inevitable that huge numbers of RC prints worldwide will h.c
material were properly manufactured, it would avoid most be similarly affected. arc
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of the stability problems associated with black-and-white Judging from the speed at which the images of framed es
RC papers (it would, however, also be more expensive). and displayed Polycontrast Rapid RC prints from the 1970’s m-r
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Before the invention of RC paper base in the 1960’s — and Polycontrast Rapid II RC prints from the early 1980’s wilh
and before opaque white polyester supports became avail- can become severely discolored, these papers could cer- w.
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able around 1980 — waterproof print supports were made tainly be ranked as some of the most inherently unstable w
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with white-pigmented cellulose acetate (in its transparent black-and-white photographic materials ever to be mar- at
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form, the same material is used for film base). Beginning keted since the introduction of the first silver-gelatin de- ate
in the early 1940’s, Kodak Minicolor and Kotavachrome veloping-out papers in the late 1800’s. The deterioration of gin
prints (processed by Kodak using the Kodachrome sys- the Kodak RC prints has occurred despite careful process- nt ori
tem) were coated on pigmented acetate supports, as was ing and washing. me
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Ansco Printon, a reversal color material for printing slides The discolorations which this author has observed in oc
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produced by Ansco from 1943 until 1973. From 1963 until Kodak Polycontrast Rapid RC prints generally are concen- s
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around 1980, Cibachrome print materials were coated on a trated along density gradients where light and dark por- T
pigmented cellulose triacetate support. With the introduc- tions of the image meet; Polycontrast Rapid RC prints some-
tion of Ilford Cibachrome II materials, the support mate- times also have large numbers of orange-red microspots.
rial was changed to Melinex 990 (in 1991, Ilford changed Deteriorated Ilford RC prints, on the other hand, usually
the name of all Cibachrome materials to Ilfochrome — have had a more uniform, overall brownish-yellow image
Cibachrome II became Ilfochrome Classic). Because of discoloration.
processing considerations, all of these color materials re- Both Kodak and Ilford RC papers can suffer from microspot
quired a nonabsorbent support; had this not been the case, formation and surface mirroring; with some prints, the
a less costly fiber-base support could have been used. mirroring has become quite extreme. Although all of the
Pigmented cellulose triacetate is a far more stable ma- deteriorated Kodak RC prints which this author has been
terial than the RC base papers of the 1970’s — but it is also able to positively identify were made on Polycontrast Rapid
more expensive. Kodak had long searched for a low-cost, RC Paper and Polycontrast Rapid II RC Paper, it is as-
waterproof substitute for pigmented cellulose triacetate. sumed that Kodabrome RC and other Kodak black-and-
Kodak wanted a material that cost little more than single- white RC papers from the period can be similarly affected.
Display and Illumination of Color and Black-and-White Prints Chapter 17 580
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Fern Bleckner, at the time a conservator at the Corcoran Gallery of Art in Washington, D.C., and Joe Cameron, a e
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photographer and teacher at the Corcoran, examine discolored black-and-white RC prints that had been made on Polycon- n Ju
trast Rapid RC Paper in the mid-1970’s. Although the prints had been displayed for only 2 months, they had nevertheless o
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developed serious image discoloration by the time this photograph was taken in 1981. It is not known whether the damage m
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was caused by exposure to light or by air pollutants (or a combination of both). At the time, the Corcoran was not air c
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conditioned, and during warm months windows in the photograph storage area, which is near to a busy Washington street, arc
were open much of the time. Pollutants from automobile exhaust might have been a significant factor in the rapid se
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deterioration that occurred in these unstable prints. m-r
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Some Kodak Polycontrast Rapid RC prints also have Light-Induced Oxidation and Subsequent w.
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suffered from severe cracking of the polyethylene-coated Cracking of the Image-Side Polyethylene Layer <w
support material (cracking has also occurred in many dis- at
epalarylye d1 9K7o0d’sa)k. EAks tdaicsocluosrs ReCd bperilnowts, fcrroamck tihneg loaft eth 1e9 6R0C’s s aunpd- ingP pooloyre tshtyalbeinliety p wlahsetnic s huabsje lcotnegd tboe epnro rloencgogedn iezxepdo assu rhea tvo- ginated
pstoorrta igs ef aocri lditiastpelday b iyn a a cno emnbviinraotnimone onft einx pwohsuicrhe tthoe l irgehlta tainvde liisgshute do rt ou lEtraasvtimolaent Kraoddiaakti ofonr. i mAcpcroorvdeimnge nttos ain 1 t9h7e4 fpoartmenut- ment ori
lation of its RC papers: u
humidity fluctuates over a wide range. With the passage of c
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time, it is expected that increasing numbers of these prints s
will develop cracks. To date, however, image discoloration In the use of such resin coated papers many Thi
problems occur, not the least of which relates
appears to be a much more serious problem than support
to the relatively low stability of the resins and,
cracking in black-and-white RC prints.
especially polyolefins [polyethylenes], used to
Ilford Ilfospeed RC paper was not particularly popular
coat the paper to achieve the desired wet
in the U.S. in the 1970’s, and this author has encountered
strength, etc. Such resins [polyethylenes] typi-
only a relatively small number of Ilfospeed RC prints that
cally deteriorate quite rapidly due to the action
have been displayed for significant periods (complicating
of, for example, ultraviolet light or the oxida-
the matter is the fact that Ilford did not imprint the back of
tive action of photographic printing and devel-
the paper with the company’s name, so it is often impos-
oping chemicals. . . . It has therefore become
sible to tell whether a particular print is in fact an Ilford
of prime importance that such resinous layers
product). This author has not yet encountered a verified
be suitably stabilized against such hazards if
Ilfospeed RC print which has developed cracks; however,
they are to be useful in photographic papers.6
cracking of Ilford RC prints from this era has been re-
ported in the literature.5
581 The Permanence and Care of Color Photographs Chapter 17
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19 pdf
1.
This small print, made on Kodak Polycontrast Rapid RC A magnified view of the RC base cracking. The fluores- s_v
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Paper from the early 1970’s, has developed severe RC cent lamps elevated the temperature inside the cabinet, HiR
base cracks. The print was exhibited for about 5 years in thus lowering the relative humidity. When the lamps 0_
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a glass-enclosed display cabinet in the Grinnell College were turned off at night, the humidity returned to the of_
Physics Museum in Grinnell, Iowa. The cabinet was illu- ambient level, and this daily humidity cycling, in combi- 7_
1
minated with bare-bulb Cool White fluorescent lamps. nation with the degrading effects of light and UV radiation k_
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(Print courtesy of Grant Gale, physics professor and cu- on the unstable RC base, eventually produced the crack- Bo
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rator of the Physics Museum) ing seen here. W
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The light-induced deterioration of polyethylene can be with by-products of polyethylene degradation (certain emul- e:
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greatly accelerated by the presence of white titanium diox- sion ingredients or other components of the RC paper struc- na
iRdCe ppirginmtes.n t ,T iintacnoriupmor adtieodx iidne t hise at opph pootolycehtehmyliecnaell yla aycetri voef tduizree) m thaey aadlsjaoc been itn sviolvlveer dim) —ag cea. n T phreo egvreesnstuivaell rye astutaltc cka (no xbie- der file
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substance and when exposed to light it can generate an severe image discoloration and the formation of “silver 3 u
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active form of oxygen, which in turn can attack adjacent mirrors” on the emulsion surface. This apparently is the 20
polyethylene. Although both ultraviolet radiation and vis- mechanism responsible for the rapid image deterioration e 6,
icbolned liitgiohnt sc aonf ltarriggeg enru mthbeesres r oefa dcetitoenrsio, rsattueddy RoCf tphrein dtsis spulagy- tmhaadt eh aosn b eeeanr loyb sKeordvaekd iann md aInlfyo frrda mbleadc ka-nadn ddi-swphlaityee dR pCr ipnats- on Jun
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gests that visible light is, in most cases, the primary cause pers. Unframed prints exposed to light can also be af- m
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of the deterioration. In typical indoor display conditions, a fected. The relative humidity of the display and storage h.c
Plexiglas UF-3 or other UV filter will probably do little to environment appears to be an important variable in these arc
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improve the long-term stability of a black-and-white RC reactions, with high relative humidity substantially increasing es
print. the rate of image discoloration. High temperatures un- elm-r
Oxidation of the polyethylene results in gradually in- doubtedly also accelerate the rate of deterioration. wilh
creasing brittleness of the plastic and, in conjunction with Internally generated peroxides and/or by-products of w.
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the physical stresses produced by normal fluctuations in polyethylene degradation may also be implicated in the <w
relative humidity (e.g., between 30 and 60%)7, will eventu- increased rates of fading that this author has observed in d at
ally cause cracks to form in the image-side polyethylene certain types of Ektacolor, Fujicolor, Agfacolor, and 3M ate
layer and print emulsion. color papers when they are framed under glass or plastic gin
Light-induced deterioration of polyethylene and accel- on long-term display. With color prints, it is of course a dye nt ori
erated test methods used by Eastman Kodak to evaluate image, rather than a silver image, that is affected (see me
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the cracking tendency of its RC papers have been reviewed Chapter 2 for discussion of RC-base-associated fading of oc
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in an important 1979 article by Parsons, Gray, and Crawford.8 color prints). s
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The addition of antioxidants and stabilizers to the struc- The sensitivity of silver photographic images to even T
ture of Kodak RC papers, the change to a less reactive very low levels of peroxides and other oxidants, especially
form of titanium dioxide in the emulsion-side RC layer, and in humid environments, is well established, and logic would
other improvements in Kodak RC papers were also de- suggest that an oxidant level sufficient to degrade and em-
scribed (the article restricted its discussion to the problem brittle polyethylene should also be capable of oxidizing the
of RC print cracking and did not deal with silver-image delicate filamentary silver grains which make up the image.
discoloration of displayed RC prints). The chemical processes involved in the oxidation and
subsequent reduction of the silver image, resulting in the
Light-Induced Destruction of formation of yellow-orange colloidal silver and “silver mir-
rors,” are also generally understood and have been dis-
the Silver Images of RC Prints
cussed at length in the literature. As described by Larry
The peroxides and other oxidants generated in the tita- Feldman of Eastman Kodak,9 the silver grains forming the
nium dioxide pigmented polyethylene layer during long- image are oxidized by peroxides or some other oxidizing
term exposure to light and UV radiation — in association substance to form silver ions. Particularly when the emul-
Display and Illumination of Color and Black-and-White Prints Chapter 17 582
sion has a high moisture content, the silver ions can physi- Polycontrast Rapid RC prints, base degradation is in the
cally migrate a short distance from the site of the original great majority of cases the primary reason that images
silver grains. Through the action of light, or in the pres- have discolored, or will do so in the future if displayed for a
ence of various atmospheric contaminants, the silver ions sufficient length of time. In the subsequent edition of Kodak
are then reduced to tiny particles of metallic colloidal sil- Publication No. G-1, released in May 1982, and a later edi-
ver, or converted to silver sulfide (silver sulfide can be tion published in 1985, all reference to a possible relation-
formed by reaction with, for example, hydrogen sulfide, a ship between RC base degradation and image discolora-
common air pollutant). According to Feldman, “Since these tion was deleted.
minute particles refract light, groupings of these particles In May 1978, at a conference on preservation of color
have a characteristic yellow, orange, or red appearance. photographs at the International Center of Photography
When concentrated near the [emulsion] surface, the me- (ICP) in New York City, this mode of black-and-white RC
tallic silver or silver sulfide particles can reflect light as a image discoloration was discussed by Klaus B. Hendriks.11
silver mirror.” Commenting on the previously discussed statement in the
Changes have been made in the structure of the silver 1978 edition of Kodak B/W Photographic Papers, Hendriks
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grains in print emulsions in recent years in order to reduce dismissed the influence of oxidants originating from the df
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the amount of silver required to produce an adequate black environment or from residual processing chemicals as likely 1.
(thus increasing the “covering power” of the silver), and causes of image discoloration in framed RC prints, and s_v
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thereby reduce the manufacturers’ costs. These changes said: “First the base degrades and produces some oxidiz- Hi
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may also be implicated in the increased susceptibility of ing agent, and then it will continue to attack itself [and the 20
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some black-and-white RC papers to image discoloration. silver image] because it is enclosed in a glass frame.” of
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Hendriks, who is director of the Conservation Research 1
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Displayed Black-and-White RC Prints Division at the National Archives of Canada, said that dis- oo
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Can Self-Destruct playing a framed black-and-white RC print created a “closed W_
system” of deterioration, and he speculated that this could <H
We have here a very alarming situation — with their prove to be a serious problem in the years to come. (When e:
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built-in ability to generate oxidants during the course of the presentation was given in 1978, neither Hendriks nor na
ntioarllmy aplo dwiseprflauyl ,s boluarccke- aonf dt-hwehiri toew RnC d persitnrtusc ctoionnta. i nW ait hpo btoetnh- tinh isth aeu tthhoern h-naedw y ebtl saecekn-a annd -ewxhaimtep lReC o f pimapaegres dwishcioclho rcaotuiolnd der file
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the silver image and support material being attacked, this definitely be attributed to this mechanism of “self-destruc- 3 u
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constitutes an entirely new type of photographic deteriora- tion”; however, a number of Ektacolor RC prints that had 20
tion. Although unframed RC prints on display are also developed cracks after less than 10 years of normal display e 6,
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RsuCb jpercitn tt ou nlidgehrt -ginladsusc eodr pimlaasgtiec dexisaccoelrobraattieosn t, hfera pmroinbgle man, in hDoamveids Vheasdt able, ean p ehnoctoogurnatpehreedr. a)nd influential writer who on Ju
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apparently by preventing the diffusion of oxidants and volatile in early 1976 had started a public campaign to alert photog- m
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degradation products into the atmosphere, and away from raphers to the shortcomings of RC papers and to convince h.c
the silver image. With everything trapped inside the frame, Kodak and other manufacturers not to cease production of arc
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and with the print emulsion sandwiched between the RC fiber-base papers, gave a detailed account of Hendriks’s es
support and framing glass, the print is left to “stew in its presentation in the October 1978 issue of Popular Photog- elm-r
own juices.” (See pages 600–601 for reproductions of RC raphy magazine in an article entitled, “RC Report: The wilh
prints that suffer from light-induced image discoloration.) TiO2 Blues.”12 ww.
Over the years Kodak has carefully avoided discussion w
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of this mode of RC image deterioration, and this author is The “Edge Effect” in the Discoloration d at
aware of only one reference — a vague one at that — in of Framed and Displayed RC Prints ate
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Kodak literature to this phenomenon. In the April 1978 gi
revision of Kodak B/W Photographic Papers, Kodak Publi- Supporting the view that image deterioration of framed nt ori
cation No. G-1, it is stated: and displayed Kodak Polycontrast Rapid RC prints can be me
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caused by oxidants generated by the RC paper itself is the oc
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In addition to protecting the paper base from nature of the discoloration observed after several years of s
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absorption of processing chemicals (thus permit- display in two RC prints made in 1977 by this author. The T
ting easier working), the resin [polyethylene] lay- photographs were taken in the middle of the night of a
ers restrict the flow of gases. When prints are lumberyard in Grinnell, Iowa going up in flames — the
stored or displayed in a confined atmosphere (such lumberyard was located next door to this author’s home
as being framed under glass), any oxidants present (which, fortunately, was spared). These prints were among
may react with the silver grains and result in im- many made by this author from a box of 8x10-inch Polycontrast
age discolorations. Such oxidants might result from Rapid RC Paper purchased in 1974;13 all of the prints had
the environment, residual processing chemicals, been carefully processed, washed, and air-dried at room
adhesives used in frame construction, cleaning temperature, following Kodak’s instructions. The white
agents, or base degradation [italics added]. . . .10 borders were trimmed from the prints after processing.
The prints were dry mounted in the centers of sheets of
Although Kodak placed “base degradation” last on its 11x14-inch, 4-ply, 100% cotton fiber museum mount board
list of potential causes of image discoloration in framed RC (made by the Rising Paper Company). The mounted prints,
prints, this author believes that at least with early Kodak without overmats, were placed under glass in metal frames.
583 The Permanence and Care of Color Photographs Chapter 17
After less than 5 years of display, severe image discolora- Polycontrast Rapid RC prints discussed above, this author
tion, microspots, and surface mirroring had occurred in subjected a small print made from the same box of paper
medium- and high-density image areas, with the discolora- to a high-intensity 21.5 klux accelerated light exposure test
tion and mirroring especially pronounced in high-density with the expectation of being able to quickly simulate the
locations adjoining low-density or white areas of the prints. discoloration. After several months had passed and the
However, the very outer edges of the prints — extending test print had been exposed to far more light (intensity x
inward about 1⁄16 inch — suffered little or no discoloration. time) than the displayed print could possibly have received
This author believes that this “edge effect” is caused by during the 5 years that it had been hanging on the wall —
the oxidants generated by the pigmented polyethylene layer and with no sign of discoloration in the test print — it was
diffusing through the paper core at the outer edges of a concluded that the discoloration mechanism must have an
print. Passing into the thin air pocket surrounding the extremely large reciprocity failure in light exposure tests.
edges of the framed print (the thickness of the print kept (If no reciprocity failure were involved, increasing the light
the mount board slightly separated from the framing glass) intensity 25 times, for example, would reduce the length of
and then absorbed by the mount board, the localized con- time for image discoloration to appear by a factor of 25 —
centrations of oxidants at the edges of the print were lower see Chapter 2 for a discussion of reciprocity failures as >
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than oxidant levels in the rest of the image area. applied to the light fading and light-induced staining of 1.p
In correctly processed and washed fiber-base prints suf- color prints.) s_v
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fering from image deterioration caused by external con- To more systematically investigate the light intensity HiR
taminants from polluted air or unsuitable storage materi- reciprocity relationship, the influence of UV radiation on 0_
2
als, it is frequently observed that the discoloration and image discoloration, and the effects of framing under glass of_
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fading are most severe near the edges of the prints. With or plastic, this author began a series of tests with samples 17
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framed and displayed RC prints, the opposite is generally cut from duplicate prints made in 1977 with paper from the ok
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true; this is additional support for the theory that the im- same box that had been used for the 5-year displayed prints. _B
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ages are oxidized by substances generated within the print All of the prints had been made during the same darkroom H
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structure itself. In the examples of discolored RC prints session and had been processed, washed and dried in the e:
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just cited, the prints showing the “edge effect” had been same manner. The duplicate prints had been stored in the a
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tproismsmibeildit ya ftthera tp erodcgees-spiennge atrnadt idorny ionfg p, rtohcuess esliinmg inchateimngic tahles dteasrtk sdaumripnlge tchoen 9t ayienaerds bae wfohriet et hbeo tredsetrs wanedre a s tfaurllt erda.n Egea cohf der file
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into the paper core of the RC prints was involved. densities — from a clean white to a deep black. 3 u
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In view of the fact that the RC print structure has two One group of prints was placed under low-intensity 1.35 20
polyethylene layers, that the prints were mounted on 4-ply, klux (125 footcandles) Cool White fluorescent illumination e 6,
100% cotton fiber museum mount board (all of which would at 75°F (24°C) and 60% RH. Another group was exposed to un
help protect the image from attack from the back by air- high-intensity 21.5 klux (2,000 footcandles) illumination, also on J
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borne contaminants), and that the print emulsions were at 75°F (24°C) and 60% RH (for a description of the test m
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protected from the environment by framing glass, the re- equipment, see Chapter 2). Illumination at 21.5 klux is 16 h.c
duced edge-fading also suggests that contaminants within times more intense than at 1.35 klux. Included were unframed arc
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the frame itself or from the surrounding environment were prints exposed to bare-bulb illumination, prints framed with es
not a significant factor in the discoloration. glass (both with and without an overmat), and prints framed m-r
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(It is important to note that unframed RC prints may with Plexiglas UF-3, a UV-absorbing acrylic sheet. wilh
also discolor. Indeed, this author had a stack of prints At the time this book went to press in 1992, the tests had w.
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sitting on a shelf in his office for a number of years, and been in progress for 6 years (72 months) and visible dete- w
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several Kodak Polycontrast Rapid RC prints among the rioration had occurred in most of the prints: at
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group discolored where the edges or corners had protruded ate
from the stack and were exposed to light. Fiber-base prints 1.1.35 klux Unframed Print: After 4 years, significant gin
in the stack were unaffected.) yellowish discoloration had rather suddenly occurred, nt ori
It has been noted by this author that after prolonged and this was most evident in medium and low density me
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exposure to light, most RC papers evolve gases that have a areas immediately adjacent to white portions of the oc
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distinct, pungent odor. The odor is especially pronounced image. Unlike the prints that were framed with glass s
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if the prints have been framed under glass or plastic. Once or Plexiglas UF-3, no microspots were evident, although T
the prints have been exposed to light for a sufficient pe- surface “silvering-out” was noted adjacent to the most
riod, emission of these gases can continue for many months, severely discolored areas. Even after 6 years, no base/
or even years, after the prints are placed in dark storage. emulsion cracking was observed with the unframed print,
The evolution of the gases is probably associated with the even though it had been exposed to the relatively high
slow decomposition of polyethylene. The exact composi- UV content of bare-bulb fluorescent illumination.
tion of these volatile substances has not been identified.
2.1.35 klux Overmatted Glass-Framed Print: After 11⁄2
Accelerated Light Exposure Tests years of light exposure, “classic” orange-colored, sur-
to Induce Silver Image Discoloration face-mirrored microspots were observed (if this author
had been experienced in looking for early-stage discol-
and Base Cracking in RC Prints
oration, the spots probably would have been noticed
In 1986, after examining the nature of the severe image sooner). These spots occurred in medium-density ar-
discoloration that occurred with the 1972 “initial type” eas, adjacent to lower-density parts of the image. After
Display and Illumination of Color and Black-and-White Prints Chapter 17 584
21⁄3 years, the spots had grown in size, but the total this pattern continued with the size and number of mi-
number of these “large” spots remained fairly small. In crospots and the degree of image discoloration becom-
addition, a narrow band of the image, approximately ing more severe.
1.0mm wide, and running along the full length of the
adjacent, untrimmed white print border, had become 7. 21.5 klux Print Framed in Contact with UF-3: After
uniformly discolored and surface-mirrored. Under 10X 21⁄3 years, the print had developed a very narrow, strongly
magnification, a large number of very small microspots discolored band along the full length of the image adja-
could be observed in an image area 3mm to 8mm from cent to the white print border; the print also exhibited
the print border. After 4 years, significant yellowish small microspots along an area farther in from the bor-
discoloration in low- and medium-density areas adja- der. Like the 1.35 klux print framed with UF-3, these
cent to white portions of the image had rather suddenly spots were concentrated near one corner of the print.
occurred. Few additional large microspots were noted. In fact, after 6 years of light exposure, the pattern of
After 6 years, this pattern continued with image discol- discoloration on these two prints was almost identical
oration becoming more severe; no surface cracking could — despite the fact that the 21.5 klux print had received
be detected. 16 times more light exposure than the 1.35 klux print! >
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1.
3.1.35 klux Print Framed in Contact with Glass: After The previously discussed severely discolored and spot- s_v
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12⁄3 years, the print had developed large numbers of ted print that had been normally displayed for 5 years (made HiR
very small microspots, which were fairly evenly distrib- on the same paper as the test samples described above), 0_
2
uted in medium- to high-density areas of the print (the was displayed under Cool White fluorescent illumination of_
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microspots tended to be concentrated along image-density with an intensity of about 195 lux — the total display time is 17
_
gradients). No discoloration was evident in low-density estimated to have been approximately 14,300 hours. The ok
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areas of the image. After 4 years, the print had not print was framed under glass, without an overmat, and for _B
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developed a discolored area next to the white print bor- most of the time, the area where it was displayed was air H
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der as had occurred with No. 2 above. But, overall, the conditioned. The length of time that had passed before the e:
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number of small microspots had increased markedly. first discolorations occurred in this print is not known. a
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Nthoen e“l aorf gteh”e ssep ostpso ttsh,a ht oowcecvuerrr,e da pwpritoha cthheed o tvheer msiaztet eodf Accumulated Light Exposure of Prints: der file
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print. After 6 years, little of the yellowish discoloration 3 u
noted in the overmatted print was evident. Print normally displayed for 5 years = 2,790 klux-hours 00
2
(estimated light exposure accumulated during 5 years) 6,
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n
4.1.35 klux Print Framed in Contact with UF-3: After u
21⁄3 years, the print exhibited a narrow, strongly discol- (12.355x klilguhxt t eexspt opsruinrtes offo rn o6r ymeaalrlsy =di s7p0l,a9y5e6d k plurixn-th)ours > on J
ored band immediately adjacent to the untrimmed white m
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print border (identical to that described in No. 2 above) 21.5 klux test prints for 6 years = 1,130,040 klux-hours h.c
and the print had also developed some small microspots (405x light exposure of normally displayed print) arc
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3mm to 10mm from the border; these spots were con- es
centrated near one corner of the sample. After 6 years, m-r
Conclusions Suggested by These Tests el
more microspots and discoloration were noted. wilh
It is clear that to produce the type of image discolora- w.
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5.21.5 klux Unframed Print: After 11⁄2 years the print tion caused by long-term display under normal conditions <w
had developed extensive emulsion and/or base crack- with this particular RC paper, accelerated light-exposure at
d
ing (which type of crack could not be determined) in tests have an extremely large reciprocity failure (although ate
minimum-density (white) and low-density areas. The the 21.5 klux test samples had received an estimated 405 gin
first cracks probably occurred at an earlier point in the times more light exposure than did the severely discolored nt ori
test; but because the cracks were not accompanied by print that had been displayed under normal conditions for me
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image discoloration, and at that time this author was 5 years, the discoloration observed in the 21.5 klux print oc
d
not consciously looking for cracks, they were not no- samples was less pronounced). Therefore, one would have s
hi
ticed. After 21⁄3 years the cracks covered most of the to conclude that — compared with long-term display under T
print surface, with only the maximum-density areas still normal conditions — short-term, high-intensity tests (at
remaining free of cracks. After 4 years, cracking was least at room temperature) may in fact do little if anything
very extensive and covered all areas of the print. Even to accelerate the discoloration process.
after 6 years of illumination, however, and with the print These results, together with an investigation of the illu-
severely cracked, no microspots or other image discol- mination history of a number of prints that became discol-
oration could be detected. ored during normal display, suggest that the threshold level
of illumination necessary to initiate the production of oxi-
6.21.5 klux Print Framed in Contact with Glass: After dants by the titanium dioxide pigmented polyethylene layer
4 years, the print rather suddenly began to show sig- may be very low indeed (and that although exposure to UV
nificant image discoloration in the form of large num- radiation appears to accelerate the reaction, visible light
bers of distinct microspots. The discoloration was most alone is quite sufficient to initiate and sustain the process).
evident in medium- and high-density areas immediately The fact that, even after 6 years of light exposure, the
adjacent to low-density and/or white areas. After 6 years, unframed print in the high-intensity, forced-air-cooled 21.5