Negatives Prints Ta p e s CDs & DVDs by Peter Z. Adelstein, Image Permanence Institute TORAGE is the single most important (ISO). The ISO standards recommend climate factor determining the useful life of conditions for the storage of specific media, CONTENTS modern information media. (For elec- and when possible, these recommendations USING THE MSQR ................................................... 1 tronic media, copying and format ob- should be followed. The standards are less A FRAMEWORK FOR MEDIA PRESERVATION .......... 2solescence are also important, but those is- helpful, however, when it comes to assessing The Three Categories of Environmentally Inducedsues are beyond the scope of this publication.) how a particular environment will affect a col- Decay ................................................................ 2The Media Storage Quick Reference (MSQR) lection or deciding on the best environment for Decay Caused by Improper Storage ........................ 2attempts to explain the role of storage condi- storing a collection that contains media of dif- Assessing Your Environment ................................... 3tions—that is, temperature (T), relative humid- ferent types—common concerns among col- Condition Assessment—A-D Strip Testing for Acetateity (RH), and air quality—in the physical sur- lection managers. The purpose of the MSQR is Film Collections ................................................ 3vival of photographs, films, audio and video to distill and present, in one publication, the Should Degraded Nitrate and Acetate Film Betapes, CDs, and DVDs. information you need to make informed deci- Segregated? ..................................................... 3 Research shows that lower temperature and sions about the storage of the mixed collec- CATEGORIZING YOUR ENVIRONMENT BY AVERAGERH can greatly improve material stability, a fact tions of photographic, magnetic, and optical TEMPERATURE .................................................. 4reflected in the standards published by the In- media in your care. SIMPLIFIED STORAGE GUIDELINES FOR MIXEDternational Organization for Standardization COLLECTIONS ................................................... 5 Air Quality ............................................................... 5 USING the MSQR Planning for COLD or FROZEN Storage ................... 6Decision-making about new or existing stor- browse for the topics that interest you most. Enclosures .............................................................. 7age facilities usually starts with one of three Table 3 on p. 5 is literally and figuratively the MEDIA SUPPORT CHRONOLOGY ............................. 8key questions: centerpiece of the MSQR. It presents an over- THE WHEEL ............................................................ 9• How good (or bad) are my existing stor- view of the suitability of storage environments GLOSSARY ............................................................ 10 age conditions? for various media types. Preservation issues REFERENCES ........................................................ 10• What storage conditions should I have for related to specific media can be found in tan the media in my collection? boxes throughout the booklet; each box con- MEDIA INDEX tains information about a specific medium, in- Photographic glass plates ................................. 2• What storage compromises can I safely cluding structure, particular preservation con- make for my collection of different media Nitrate base photographic film ......................... 3 cerns, ISO recommendations, and simplified types? Acetate base photographic film ........................ 4 storage recommendations. The light blue boxes These questions are answered throughout present important side issues such as low-tem- Polyester base photographic film ..................... 4this booklet and on the MSQR wheel. perature storage, enclosures, environmental as- Photographic paper prints ................................. 6The Booklet sessment, and condition assessment. Ink jet prints ................................................. 6These pages are not laid out in strictly linear Magnetic tape ........................... 7 The Wheelfashion for cover-to-cover reading but rather CDs and DVDs ...................... 7 An important component ofin discreet blocks of interrelated information the MSQR is the two-sidedas illustrated in Fig. 1. You may find it useful to wheel (Fig. 2), which can be found in the pocket at Text under blue and the back of the booklet. white headings: general Side 1 of the wheel, the preservation overview and guidelines for Media Storage Summary, understanding and provides a medium-by-me- applying simplified dium overview of preserva- storage recommenda- tion issues (kinds of decay or tions. other problems), recommenda- Blue boxes contain tions (key storage considerations), important side issues and simple guidance on the suitability of related to collection four typical environments, ROOM, COOL, care. COLD, and FROZEN. The Media Support Chro-Tan boxes offer information on specific media: nology on Side 2 is a guide to the types andstructure, key preservation issues, ISO recommenda- dates of use of nitrate, acetate, and polyestertions, and simplified storage recommendations. Fig. 2. The Media Storage Summary is on Side 1 of the plastic supports for various film and magnetic MSQR wheel. The Media Support Chronology is onFig. 1. Guide to navigating the MSQR. tape media. Side 2.
A FRAMEWORK for MEDIA PRESERVATION ithout a lock on the door, a roof over- rioration are in order. In practice, you must know • The behavior of the different media types head, and some degree of orderly ar- the current decay status of your collections and in your collectionrangement, a media collection has little chance have reliable data on their actual storage con- • Their current state of preservationof survival. Once these basic conditions for ditions. You need three pieces of information • The prevailing storage conditions.preservation are satisfied, however, the most to make good storage decisions:urgent problem is slow but steady decay. Somemedia, CD-ROMs, for example, decay slowly The Three Categories of Environmentally Induced Decayand can tolerate a variety of storage conditions.Most other media decay much faster and need The three general categories of environmentally in- is a major threat to media that have color dyes and/ duced deterioration are biological, chemical, and me- or nitrate or acetate plastic supports. COLD storagespecial environments to have a long useful life. chanical (or physical). is recommended for these materials; FROZEN is rec- Each medium has its Achilles’ heel and its ommended when signs of deterioration are present. Biological Decayown special requirements. The dyes in color Mechanical Decay Biological decay includes all the living organismsphotographs spontaneously fade at room tem- that can harm media. Mold, insects, rodents, bac- Mechanical forms of decay are related to theperature in a rather short period of time; low- teria, and algae all have a strong dependence on changes in size and shape of water-absorbing ma-temperature storage is the only way to preserve temperature and RH. Mold and mildew are serious terials such as cellulosic plastic film supports orthem. Black-and-white photographic prints dangers to media collections. Sustained high RH the gelatin binder in photographic materials. RH is (above 70% or so for more than a few days) should the environmental variable that determines howdon’t require low-temperature storage, but the be avoided. much water is absorbed into collection objects.silver particles making up the images are very When the RH is very low (below about 15%) forsensitive to high humidity and airborne con- Chemical Decay long periods of time, objects lose moisture andtaminants. Media preservation depends on our Chemical decay is due to spontaneous chemical shrink. The opposite is true when RH remains highunderstanding of the vulnerabilities of each me- change. Fading of color dyes in photographs and (above 70%). Expansion due to extreme dampness degradation of binder layers in magnetic tape are and contraction due to extreme dryness causedia type so that we can provide the proper stor- examples of decay caused by chemical reactions stresses among the layers of media objects, whichage conditions. For new, undeteriorated mate- occurring within the materials themselves. The can lead to permanent deformation and layer sepa-rials that will be kept in purpose-built storage speed of these reactions depends primarily on tem- ration.facilities, this task is relatively straightforward. perature, but moisture also plays a role. In general, Excessive dampness is a very serious environ- the warmer the temperature of the storage area, andBut when some elements of the collection are mental threat to media collections because it con- the higher the RH, the faster the media collection tributes not only to mechanical decay but to bio-older or already deteriorated, storage conditions will be affected by chemical decay. Chemical decay logical and chemical decay as well.that dramatically slow down the rate of dete- Photographic Glass Plates Decay Caused by Improper Storage STRUCTURE The ten types of decay listed in the table are major several types. The good news is that the proper en- Silver image particles threats to media collections. Some forms of decay vironment will effectively minimize the risk of de- in a gelatin binder on may affect only one media type; others may affect cay-related damage. glass support. PRESERVATION ISSUES Decay Related to Temperature and RH Table 1: The types of decay that threaten media, the media that are affected, and recommended storage environments. • Silver image decay • Glass deterioration • Layer separation. The glass support is dimensionally stable in changing humidity, but the gelatin binder is not and will contract at low humidity. If the stress between the contracting binder and the glass is greater than the adhesion between the gelatin and the glass, the two layers will separate. • Mold Other Concerns • Harmful enclosures • Breakage. Handling and enclosure guidelines are given in ISO 18918.7 • Poor air quality ISO RECOMMENDATIONS7 Max temp: 64°F (18°C). RH from 30% to 40%. Lower humidities can cause layer separation. SIMPLIFIED STORAGE RECOMMENDATIONS COOL temperature ensures greater protection from image decay. FROZEN is not recommended because of possible layer separation.2
Assessing Your EnvironmentGetting Data Fluctuations IPI Analysis ToolsKnowing the temperature and RH conditions in your Fluctuations in temperature and RH are always a IPI has developed software especially for the com-storage environment is a critical part of preserva- concern in environmental assessment. Fortunately, plex job of analyzing temperature and RH data. IPI’stion practice, but this is impossible without reliable short-term RH fluctuations generally are not much Climate Notebook software can accept data fromdata. Storage areas should be continuously moni- of a threat to media collections and should not cause a variety of dataloggers, perform quantitative deter-tored. Electronic temperature and RH sensors that alarm. The level of sensitivity to environmentally in- minations of the overall rate of chemical decay andallow data to be analyzed on computers are pre- duced mechanical damage is fairly low for most me- the risk of mold growth, and generate automatedferable; sophisticated analysis or visualization of dia. In addition, enclosures such as boxes and cans reports and analyses tailored to the specific needslong-term trends is difficult to do with char t tend to buffer fast RH changes. Maintaining steady of media collections. IPI has also developed a data-recorders. Many kinds of electronic dataloggers are conditions should not be the objective, if it must be logger designed explicitly for preservation use calledavailable on the market. In some cases, tempera- achieved at the cost of low temperature and RH. For the Preservation Environment Monitor (PEM).ture and RH data may be obtained from computer- the stability of media collections, the key concerns These tools make it possible to perform environ-ized systems that control the air-conditioning equip- are long-term average temperature and RH and the mental assessments that relate directly to preser-ment in buildings. profile of seasonal changes. The most important en- vation concerns. More information is available at vironmental trends are usually seasonal in nature. www.rit.edu/ipi and www.climatenotebook.org.Condition Assessment—A-D Strip Testing for Acetate Film Collections Should Degraded Nitrate andAcetate-base materials are inherently prone to a type Acetate Film Be Segregated?of chemical decay known as vinegar syndrome.1 As Nitrate and acetate films that have already deterioratedthe decay progresses, materials become more can emit acidic gases that may be absorbed by otheracidic, degrade at an ever faster rate, and eventu- film stored nearby. It is possible that absorption of acidically are irreversibly damaged. Unless preventive and oxidizing vapors from degrading films can accel-measures are taken, any acetate-base collection erate decay among undeteriorated films in the sameeventually will be lost. To know the risk of material storage area. Severely deteriorated nitrate films (thoseloss in your acetate collection and implement a showing extreme brittleness, gelatin softening, andsound preservation strategy, you must first know Fig. 4. Testing with A-D Strips. other signs of advanced decay) should be removedthe overall condition of the collection. from collections and safely disposed of. In practice, Fig. 5. Strip color is compared to however, it is usually not practical or desireable to sepa-What Are A-D Strips? the color scale printed on the rate either degraded acetate or early-stage deterioratedA-D Strips are used to determine the extent of chemi- accompanying pencil. nitrate film from the rest of the collection. The rate ofcal decay in acetate-base collections. These small decay of “good” film depends much more heavily on moving images) and magnetic soundindicator papers turn from blue, through shades of temperature than it does on the amount of acid vapor recordings. Collections of these ma-green, to yellow in the presence of the increasing the film may have absorbed from “bad” neighbors. In terials are often large, and conditionamounts of acidic vapor given off by decaying ac- addition, adequate ventilation and fresh air exchange evaluation is essential. Testing a ran-etate. In this way, the strips indirectly measure the can greatly mitigate the threat of contamination. dom sample of a collection with A-Ddegree of decay in an acetate material. Fig. 3 illus- Strips can give an idea of the collection’s overalltrates the relationship between the color change in condition. The sample size will depend on the sizean A-D Strip and rising acidity in a decaying acetatematerial. Four color levels (ranging from A-D Strip of the collection and the desired level of confidence Nitrate-Base Photographic Film in the data analysis. Statistical models can be ap- Structurelevel 0 to A-D Strip level 3) characterize the advance plied. As a rule of thumb, randomly testing aboutof decay. The higher the number, the greater the risk Silver image particles 1,000 items will provide sufficient information for aof material loss due to acetate decay. At A-D Strip in a gelatin binder on collection of 10,000 items or more. The task of test-level 2 physical property changes (e.g., brittleness, nitrate base. ing every item in a large collection is daunting anddistortion, or shrinkage) are imminent. PRESERVATION ISSUES is usually impractical; it is best to start by testing a The testing method is simple. An A-D Strip is random sample. If pockets of materials are found to Decay Related to Temperature and RHplaced in a confined space with the item to be tested be affected by acetate decay, these could be tested • Silver image decay(Fig. 4). After exposure, the resulting strip color is further, if desired, after the overall condition is as-compared to the A-D Strip color scale (Fig. 5). In- • Nitrate decay. May cause yellowing, buckling, sessed or whenever institution resources make itformation about A-D Strips and their use can be distortion, and shrinkage of film and corrosion of possible.found in the User’s Guide for A-D Strips (available metal cans. Can also cause silver image decay.on-line at www.rit.edu/ipi). What Do We Do with the Results? • Binder degradation. Nitrate base decay may Be prepared to act on your survey results. Now that cause gelatin binder to become soft or sticky.Testing—Which Materials, How Many you have a general picture of the collection’s condi- • MoldSamples? tion and know whether or not the situation is urgent, Other ConcernsAcetate-base materials include film (both still and you can respond appropriately. Most importantly, • High flammability the data will tell you how much of the collection is in critical condition. Ac- • Harmful enclosures etate materials displaying A-D Strip • Poor air quality level 2 or above are considered to be • Off-gassing. Degrading nitrate base emits in poor to critical condition and should acidic and oxidizing gases that threaten nearby be stored under FROZEN conditions materials. (see Table 3) and/or duplicated. COLD ISO RECOMMENDATIONS3 storage conditions are fine for collec- tions unaffected or only slightly af- Max. temp: 36°F (2°C). RH from 20% to 30%. fected by acetate decay. Condition as- SIMPLIFIED STORAGE sessment tells us what type of stor- RECOMMENDATIONS age the collection requires. A well-bal- COLD is consistent with the anced strategy will involve providing ISO recommendation. If there adequate storage, prioritizing duplica- is evidence of base degrada- tion, and planning ongoing condition tion, FROZEN should be used.Fig. 3. Relationship between A-D Strip levels, film acidity, and film monitoring.condition. 3
Acetate-Base Photographic Film CATEGORIZING YOUR ENVIRONMENTBLACK-AND-WHITE COLOR by AVERAGE TEMPERATURESTRUCTURE STRUCTURESilver image particles Organic dye image ollectively, the ISO standards for individualin a gelatin binder on layers in a gelatin media contain seven different temperatureacetate base. Some binder on acetate recommendations. To simplify the evaluationsheet films may have base. Some sheet and planning of storage conditions for mixeda gelatin backcoating. films may have a gelatin backcoating. media collections, the MSQR divides the rangePRESERVATION ISSUES PRESERVATION ISSUES of possible temperatures into four categories:Decay Related to Temperature and RH Decay Related to Temperature and RH ROOM, COOL, COLD, and FROZEN.• Silver image decay• Acetate decay. May cause distortion, • Color image decay2 The Four Temperature Categories shrinkage, and brittleness. Often detected by • Acetate decay. May cause distortion, Even though each of the four categories repre- vinegar odor (vinegar syndrome); severity can shrinkage, and brittleness. Often detected by be determined with A-D Strips. vinegar odor (vinegar syndrome); severity can sents a range of temperatures, it is useful here• Mold be determined with A-D Strips. to define ROOM, COOL, COLD, and FROZENOther Concerns • Mold by single “anchor-point” values, as shown in• Harmful enclosures Other Concerns Fig. 6 below. (It should be remembered that, in• Poor air quality • Poor air quality reality, the effect of temperature on decay rate• Outgassing. Degrading acetate releases acidic • Outgassing. Degrading acetate releases acidic is a continuum. The higher the temperature, the gases that threaten nearby materials. gases that threaten nearby materials. faster the decay, and vice versa.) Using Fig. 6ISO RECOMMENDATIONS6 ISO RECOMMENDATIONS6 and data gathered through an environmental as-Max. temp. depends on max. RH. Max. temp. depends on max. RH. sessment, you should be able to place your36°F (2°C) max. temp. for 50% max. RH. 14°F (-10°C) max. temp. for 50% max. RH. storage environment in one of these four cat-41°F (5°C) max. temp. for 40% max. RH. 27°F (-3°C) max. temp. for 40% max. RH. egories. It’s very likely that your storage tem-45°F (7°C) max. temp. for 30% max. RH. 36°F (2°C) max. temp. for 30% max. RH. perature is not precisely one of the four shownSIMPLIFIED STORAGE SIMPLIFIED STORAGE in Fig. 6. In this case, the following rules ofRECOMMENDATIONS RECOMMENDATIONS thumb should help you decide where your en-COLD with 50% max. RH is COLD with 50% max. RH is vironment fits:similar to the ISO recom- less stringent than the ISO recommendation but will 1. Any environment with an average tempera-mendation. If the A-D Stripreading is 2 or greater, film provide satisfactory image ture at or below 32°F (0°C) can be consid-should be stored at the stability for over 300 yrs.2 If ered FROZEN.FROZEN condition and the A-D Strip reading is 2 or 2. If your real-life average temperature is closerduplicated as soon as greater, film should be stored at the FROZEN condition and duplicated as soon to one anchor-point temperature than an-possible. as possible. other, simply apply the category it is closest to. For example, if your storage temperature is 50°F (10°C), your environment would be considered COOL.Polyester Base Photographic FilmBLACK-AND-WHITE COLOR 3. If your average temperature is about equi-STRUCTURE STRUCTURE distant from the temperatures on either side,Silver image particles Organic dye image consider both the cooler scenario and thein a gelatin binder on layers in a gelatin warmer scenario when referring to Table 3.polyester base. binder on polyesterPRESERVATION ISSUES base.Decay related to T/RH conditions PRESERVATION ISSUES• Silver image decay Decay Related to Temperature and RH• Mold • Color image decayOther concerns • Mold• Harmful enclosures Other concerns• Poor air quality • Harmful enclosuresISO RECOMMENDATIONS6 • Poor air qualityMax. temp: 70°F (21°C). Max. RH: 50% ISO RECOMMENDATIONS6SIMPLIFIED STORAGE Max. temp. depends on max. RH.RECOMMENDATIONS 14°F (-10°C) max. temp. for 50% max. RH.COOL with 50% max. RH 27°F (-3°C) max. temp. for 40% max. RH.recommended to minimize 36°F (2°C) max. temp. for 30% max. RH.possibility of silver image SIMPLIFIED STORAGEdecay. RECOMMENDATIONS COLD with 50% max. RH is less stringent than the ISO recommendation but will provide satisfactory image Fig. 6. The four temperature categories. In this context, stability for over 300 yrs.2 ROOM, COOL, and COLD are characterized by one “anchor-point” temperature. FROZEN applies to temperatures of 32°F (0°C) and below.4
SIMPLIFIED STORAGE GUIDELINES for MIXED COLLECTIONS he impact of ROOM, COOL, COLD, and Table 2. Qualitative rating system. Which Environment for Mixed Media FROZEN environments can be different for Collections?different media. Before making any storage de- The challenge of providing proper storage forcisions, you must assess an environment’s collections of mixed media types can be met inharmful or beneficial effects on the stability of two ways. You can either provide a number ofthe materials you have in your collection. special storage environments to accommodate the different types of media in your collection,Rating Storage Suitability or you can make an educated compromise andThe qualitative rating system defined in Table 2 define one adequate environment for all mate-is based on stability studies, ISO recommen- rials in that collection. The color-coded ratingdations, and evidence gathered from the field. system in Table 3 visually helps you choose aThe terms No, Fair, Good, and Very Good were suitable environment for a particular collection.chosen to reflect the appropriateness of an en- can find a qualitative rating of its suitability for the You can see at a glance that a COLD environ-vironment for a specific medium. No means media of interest in Table 3. The table shows that ment would be suitable for preserving a col-that the environment is likely to cause signifi- most media should not be kept in ROOM condi- lection containing all twelve media types dis-cant damage. Fair, Good, and Very Good can tions, as indicated by the large number of No rat- cussed here. COOL and FROZEN environmentsbe seen as indicators of increasing benefits for ings. It also indicates that all media types can be would also be suitable for certain mixed col-material stability. safely stored in a COLD environment. For all four lections, depending on their contents. When you environments, RH should be kept between 30% know what the contents of a mixed collectionUsing Table 3 and 50%. are, you can use Table 3 to find a “comfortTable 3 addresses two key questions: Is the zone” for long-term preservation.current storage environment adequate? What Starting with the Mediumenvironment does the collection really need? Table 3 also can help you determine the proper What About Deteriorating Materials? storage environment for a particular medium. A material’s current condition is a key factor inStarting with the Environment It shows which environment to avoid and which determining its storage requirements. The foot-Having categorized your environment, you can environment will work for long-term preserva- note in Table 3 points out that degrading nitratedetermine if a media collection is safe and if other tion of that medium. This information can be and acetate materials need FROZEN storage fortypes of media can be stored in the same envi- useful in planning a new storage facility or in optimum stability. (Assessing the condition ofronment. If you have determined that your envi- deciding if a particular medium can be stored acetate-base collections using A-D Strips is dis-ronment is ROOM, COOL, COLD, or FROZEN, you in an existing storage space. cussed on p. 3.)Table 3. Suitability of environments for storage of various media types. NOTE: Degrading acetate and nitrate should be frozen. The ratings for both black-and-white photographic prints and ink jet prints reflect their susceptibility to pollutants and contaminants. Air Quality Proper storage for media collections should include automotive exhaust and industrial processes, but they by these filters as the air is recirculated. Filters to re- some means to control solid and gaseous contami- also can be produced inside by deteriorating materials move gaseous pollutants from the outside are less nants in the atmosphere. or poor-quality enclosures. Pollutants released by a common. Charcoal filters remove ozone and some degrading material may affect adjacent materials in a other gaseous pollutants fairly efficiently, but they are Particulates storage area. Activities such as photocopying, general less effective with nitrogen dioxide (NO2). Potassium Particulates are very small-diameter solids that settle maintenance, or construction can introduce ozone, permanganate media can remove NO2. on surfaces in storage spaces. They can come from formaldehydes, ammonia, and other pollutants. Ozone If particulate or gaseous pollutants are a problem outside (if no filtration is provided) or be produced in- and nitrogen dioxide are oxidizing pollutants that are in your institution, a plan should be made to measure side (debris from deteriorating materials or human ac- damaging to organic dyes, silver images, and image the level of contamination and determine its source. tivity). Particulates in the form of dust and grit can cause binders. As a general precaution, bag filters should be cleaned surface abrasion, and they can also be reactive to- and gaseous pollutant filters should be changed regu- ward images. Dealing with Pollutants larly. Consult your facilities department about the types Most large commercial buildings have cloth or “bag” of systems your institution has and about the mainte- Gaseous Pollutants filters to capture particulates as they enter the build- nance schedule. These come mostly from outside sources, such as ing. Internally produced particulates are also reduced 5
Planning for COLD or FROZEN StorageWhat Are the Options? by controlling the climate in the entire storage area. ethylene freezer bags and heat-sealable bags com-The equipment you choose for COLD or FROZEN While the initial investment is large, this approach posed of layers of aluminum foil and polyethylenestorage depends on the size of your collection. Large is cost-effective and convenient in the long run. Spe- and polyester have been successfully used for COLDcollections might dictate the construction of insu- cial packaging is not needed. and FROZEN storage.2lated rooms or prefabricated walk-in chambers. Refrigerators and Freezers Avoiding CondensationHousehold-size refrigerators or freezers are options Household-size frost-free freezers or refrigerators While there is no particular risk in moving materialsfor small collections. are suitable for smaller media collections. With directly into suitable COLD or FROZEN storage (seeWhat Should the Equipment Do? these, humidity can be managed through the use of Table 3 for materials that shouldn’t be frozen), re- a packaging system that will control the moisture moving them from refrigerated spaces into warmerA COLD or FROZEN storage area must be able to level in the materials. While moisture-proof pack- areas incurs the risk of condensation on the materi-provide not only low temperatures but also humid- aging is used to avoid the incursion of moisture into als’ surface. A temperature- and RH-controlled ac-ity control. This can be achieved with a dehumidifi- the materials, the other side of the coin is that any climatization chamber is one solution to this prob-cation system or by packaging materials in mois- moisture present in the materials prior to packaging lem. Another is to use an additional water-proof en-ture-proof enclosures. Both approaches are valid, will be sealed inside. The procedure can only be closure, such as a plastic bag or other container, inbut each has advantages and limitations. successful if materials are conditioned to moderate which materials can be placed for the warming-upClimate-Controlled Rooms RH before being enclosed in moisture-proof hous- period.2 Such packaging is not needed for materialsDesiccant-based dehumidification units are recom- ing. Materials can be conditioned by being left for already in moisture-proof housings. An overnightmended for spaces housing medium-size or large one to three weeks (time depends on media type or one-day warming period prior to using the mate-collections, where proper storage is best provided and format) at ROOM conditions. Reclosable poly- rials is recommended.Photographic Paper Prints Ink Jet PrintsBLACK-AND-WHITE COLOR STRUCTURESTRUCTURE STRUCTURE The color image canSilver image particles Organic dye image consist of either dye-in a gelatin binder on layers in a gelatin based or pigmentedpaper base. Two binder on paper inks (the latter is generally the more stable of thetypes of paper are used. Fiber base (the older base. Two types of two). The image may be on paper having either atype) is a high-quality paper with low lignin paper are used. Fiber base (the older type) is a swellable polymer coating, which better protectscontent coated with a barium sulfate (baryta) layer high-quality paper with low lignin content coated the image from the environment, or a microporousto impart surface smoothness. After 1968, this with a barium sulfate (baryta) layer to impart coating, which has the advantage of faster dryingwas largely replaced by resin-coated (RC) paper, surface smoothness. After 1968, this was largely time. The image also may be printed on plainwhich has a polyethylene layer on each surface. replaced by resin-coated (RC) paper, which has a (uncoated) papers.RC paper features lower water absorption and polyethylene layer on each surface. RC paper PRESERVATION ISSUEStherefore faster processing speeds. It also features lower water absorption and therefore Decay Related to Temperature and RHproduces flatter prints. The polyethylene layer on faster processing speeds. It also produces flatter • Color image decay. Yellowing or staining maythe image side is pigmented with titanium dioxide. prints. The polyethylene layer on the image side is occur.PRESERVATION ISSUES pigmented with titanium dioxide. • Color bleeding. More likely to occur at highDecay Related to Temperature and RH PRESERVATION ISSUES humidity.• Silver image decay Decay Related to Temperature and RH • Mold• Mold • Color image decay Other ConcernsOther Concerns • Mold • Harmful enclosures• Harmful enclosures Other Concerns • Poor air quality. Atmospheric pollutants, such• Poor air quality • Harmful enclosures as ozone, may cause severe image deteriora-• Silver image decay. Degradation of the • Poor air quality tion, particularly with dye images on a pigmented polyethylene layer on RC papers ISO RECOMMENDATIONS8 microporous coating. may cause silver image decay when framed Max. temp. depends on max. RH. ISO RECOMMENDATIONS8 prints are exposed to light. 27°F (-3°C) max. temperature for 50% RH. NOTE: 27°F (-3°C) max. temp. for 50% max. RH.ISO RECOMMENDATIONS8 ISO has not yet established storage recommenda- 36°F (2°C) max. temp. for 40% max. RH.Max. temp: 64°F (18°C). Max. RH: 50%. tions specific to inkjet prints. Until it does, the SIMPLIFIED STORAGE conditions specified for color photographic printsSIMPLIFIED STORAGE RECOMMENDATIONSRECOMMENDATIONS apply to ink jet. COLD with 50% max. RH is SIMPLIFIED STORAGECOOL with 50% max. RH less stringent than the ISO RECOMMENDATIONSrecommended to minimize recommendation but willpossibility of silver image COLD with 50% max. RH is provide satisfactory imagedecay. stability for over 300 yrs.2 less stringent than the ISO recommendation, but experience indicates that this should be satisfactory. A CONSUMER GUIDE TO TRADITIONAL AND DIGITAL PRINT STABILITY — created by Image Permanence Institute with support from Creative Memories We often consider the long-term stability of color prints only after it is too late to take action to save them in their original form. This eight-page guide offers insight into some of the causes of image deterioration and suggests ways to make photographic and digital color prints last longer. Now avail- able on the Web in PDF format at www.rit.edu/ipi and www.creativememories.com/stability.pdf.6
EnclosuresWhat They Should Do, What They Can’t Do viding new, more inert enclosures is a desirable Key Points from the ISO StandardsStorage enclosures should aid in the protection, or- aspect of preservation practice, improving the cli- • All product components should pass the photo-ganization, and identification of collection items. mate is more effective overall. Environmental im- graphic activity test (PAT).Their primary function is shielding those items from provements will simultaneously reduce risks asso-dust and physical damage. Some products adver- ciated with harmful enclosures, airborne pollutants, • Plastics: Do not use PVC or acetate; do use polyes-tise additional protection from airborne pollutants and the inherent instability of the collection materi- ter, polypropylene, or polyethylene.and/or excessive humidity, although standards to als themselves. • Papers and paperboards: Neutral-sized, lignin-free,evaluate their effectiveness are lacking. Enclosures Enclosures should meet the requirements speci- buffered materials are recommended (see ISO stan-also provide surfaces for labeling as well as rigidity fied in ISO 14523 and ISO 18902.4,5 The primary dard for buffer limits).5for safe handling. However, enclosures cannot over- materials used to manufacture storage products are Storage materials should be chemically andcome deficiencies in the storage climate. paper, paperboards, plastics, and metals. Some- physically stable. Ideally, their life expectancies Some enclosures contain components that can times adhesives and metal fasteners are included should approximate or exceed those of the materi-harm materials stored in them and should be to create and/or reinforce structure. Requirements als they house. Also, their size and strength shouldavoided. As temperature and humidity rise, any for each material type are given in the ISO standards. be appropriate for the shape and weight of the ob-harmful effects from enclosures also rise. While pro- jects stored in them.Magnetic Tape CDs and DVDsACETATE POLYESTER STRUCTURESTRUCTURE STRUCTURE CDs have aA recording layer A recording layer complexof magnetic of magnetic structure andparticles (iron particles (iron are made up of CD-ROMoxides) in a oxides, metalic at least threepolymer (polyurethane) binder on thin acetate iron or chromium dioxide) and pigments in a layers: asupport. The binder may also include lubricants. polymer (polyurethane) binder on thin polyester polycarbonateThe back of the tape may have a coating of support. The binder may also include lubricants. support, apigments and a polymer binder to improve The back of the tape may have a coating of reflectivedurability and playback. pigments and a polymer binder to improve aluminum or CD-RPRESERVATION ISSUES durability and playback. gold layer, and PRESERVATION ISSUES a protective coating. Recordable CDs (CD-Rs) andDecay Related to Temperature and RH magneto-optical (MO) discs have an additional• Acetate decay. May cause distortion, Decay Related to Temperature and RH laser-sensitive layer coated on the support. DVDs shrinkage, and brittleness. Often detected by • Binder degradation. Causes uneven tape are even more complex, consisting of two CDs vinegar odor (vinegar syndrome); severity can transport, tape sticking, magnetic shedding, bonded with an adhesive. The polycarbonate be determined with A-D Strips. and layer separation. supports form the outside layers of the laminate.• Binder degradation. Causes uneven tape • Mold Different DVD formats have different layer transport, tape sticking, magnetic shedding, Other Concerns structures. and layer separation. PRESERVATION ISSUES • Poor air qualityOther Concerns Decay Related to Temperature and RH • Lubricant exudation. Separation of the• Poor air quality lubricant from the binder layer is possible when • Loss of disc integrity. Under adverse storage,• Outgassing. Degrading acetate releases acidic tape is stored at temperatures below 52°F possible defects are layer separation, lack of gases that threaten nearby materials. (11°C). planarity, cracking, and pinholes. Large and• Lubricant exudation. Separation of the • Magnetic fields. Storage near high-intensity rapid temperature and RH fluctuations can be lubricant from the binder layer is possible when magnetic fields must be avoided. particularly detrimental. tape is stored at temperatures below 52°F • Fragility. Magnetic tape is thin and fragile and • Corrosion. May occur due to high RH. (11°C). must be handled with care.11 • Mold• Magnetic fields. Storage near high-intensity ISO RECOMMENDATIONS9 Other Concerns magnetic fields must be avoided. Max. temp. depends on max. RH. • Poor air quality. Pollutants can cause• Fragility. Magnetic tape is thin and fragile and corrosion of the metallic reflective surface. 52°F (11°C) max. temp. for 50% max. RH. must be handled with care.11 63°F (17°C) max. temp. for 30% max. RH. • Magnetic fields. MO discs must not be storedISO RECOMMENDATIONS9 near a high-intensity magnetic field. 73°F (23°C) max. temp. for 20% max. RH.Max. temp. depends on max. RH. • Light exposure. CD-R discs must not be SIMPLIFIED STORAGE52°F (11°C) max. temp. for 50% max. RH. subjected to prolonged light exposure. RECOMMENDATIONS63°F (17°C) max. temp. for 30% max. RH. COOL is consistent with ISO ISO RECOMMENDATIONS1073°F (23°C) max. temp. for 20% max. RH. recommendation for 50% max. 70°F (21°C) for 50% max. RH.SIMPLIFIED STORAGE RH. COLD may cause lubricant SIMPLIFIED STORAGERECOMMENDATIONS separation with some tape for- RECOMMENDATIONSCOOL with 50% max. RH is mulations. COOL and COLD consideredconsistent with ISO optimum. FROZEN notrecommendation for 50% recommended because ofmax. RH. COLD is recom- concerns about layermended because risk of separation.lubricant separation isconsidered to be less likelythan acetate base degradation. If the A-D Stripreading is 2 or greater, tape should be stored atthe FROZEN condition and copied as soon aspossible. 7
MEDIA SUPPORT CHRONOLOGY he life expectancy of a recording medium Table 4. Chronology of selected media formats. depends in part on the stability of the ma-terial supporting the recording layers. Becausethese support materials differ widely in stabil-ity, being able to distinguish them is key toknowing how long certain portions of your col-lection might last. In the context of collectionpreservation, a nondestructive identificationprocedure is preferred and is often required. TABLE 4Table 4 and the Media Support Chronology(Side 2 of the wheel) offer information to as-sist in identifying the principal support materi-als for film and tape media.Using the Media Support Chronology andTable 4Nine categories of recording media are pre-sented on Side 2 of the wheel. Three windows,representing the three plastic support materi-als most commonly used with these media,reveal the periods of widest use for each me-dium/support combination.* If you can placea film or tape in one of the media categoriesand you know its age, you will be able to deter-mine its support material. If, for example, youknow that a roll of microfilm dates from 1935,you will learn by looking at the wheel that it ismost likely on acetate support. The stability of nitrate base is highly vari- sheets.1 As mentioned, a roll of polyester pho- The life expectancy table on Side 2 tells how able. This support was last manufactured over tographic film transmits more light than acetatelong several of the most common film supports 50 years ago, and the least stable specimens when held up to a light source and viewed edge-can be expected to remain in useful condition already have been lost. However, some cellu- on. Shaking a single sheet of polyester makeswhen stored at 68°F (20°C) and 50% RH. lose nitrate supports are more stable than the a “tinny” sound. Format can be a clue to the identity of a film more recent cellulose acetate materials. Polyester has markedly greater strength andor tape support. Table 4 lists formats, dates of Acetate chemical stability than nitrate or acetate.introduction, and types of support for a selec-tion of media. Several modifications of cellulose acetate were Magnetic Tape Supports manufactured after the 1920s. When celluloseFilm Supports Magnetic tape need not be transparent, but it triacetate became available in 1949, cellulose is very thin and must withstand the physicalNitrate nitrate was discontinued. stresses of use. Polyvinyl chloride was usedWhen photographic film was first introduced Acetate film is usually edge-marked with the for early magnetic tapes. Between 1934 andin the 1890s, cellulose nitrate was the only word “SAFETY.” When held up to a light source 1963, cellulose acetate materials were em-available plastic. It had many of the necessary and viewed edge-on, acetate photographic film ployed, primarily for audio tape. Since 1956properties, but it also had the serious disad- in roll form transmits very little light compared polyester has been the choice for video, andvantage of high flammability. Nitrate was gradu- to polyester, which also has the “SAFETY” computer tape because of its greater strength.ally replaced by the cellulose acetate family. marking. The same light transmission method used Nitrate film produced after 1930 is usually Like nitrate film, acetate film displays unique for distinguishing acetate and polyester photo-edge-marked “NITRATE.” The observable signs signs of decay, which can help in identifica- graphic film can be used for magnetic tape; inof decay that are unique to nitrate film can pro- tion. For more detail,see Acetate-Base Photo- this case, however, the behavior of the two ma-vide clues to its identity as well. See Nitrate- graphic Film (p. 4.) terials is reversed. Acetate tape rolls transmitBase Photographic Film on p. 3. Polyester more light than polyester tape rolls when held Polyester support was introduced in the mid- up to a light source and viewed edge-on.*Exact dates cannot be given for every material. In 1950s. The original polyester support was poly- Magnetic tape on acetate base is subject tosome cases, historical records are no longer available. ethylene terephthalate. In 1996, a modification, the same types of decay as acetate photo-The choice of support materials sometimes varies polyethylene naphthalate, was marketed for graphic film. Polyester magnetic tape is muchamong manufacturers and geographic locations. Some amateur roll film. more stable.plastics are not included on the wheel because theyhad limited use—for example, polyester base for ama- Polyester film is easily identified by the colorteur movie film, polycarbonate for aerial film, and poly- fringes that appear when it is viewed by trans-vinyl chloride and polystyrene for graphic arts film. mitted light through two polarized plastic8