Care of Archival Compact Discs

ConserveO Gram September 1996 Number 19/19 Care Of Archival Compact Discs Compact Discs (CD) have many advantages. Why CDs Fail Researchers search speedily through large quantities of documents on CDs, while Most CDs fail because of: protecting the original materials from excessive • Physical stress leading to delamination, handling. An inexpensive distribution tool, CDs warping, and/or improper tracking hold large quantities of data in a small space. • Dirt or grit scratching media and leading to During playing, no contact occurs between the losses of information playback device and the sound carrier so wear is • Yellowing of the plastic or light recording minimized. Many CDs incorporate an Error layer Detection And Correction (EDAC) system that • Low reflectivity due to oxidation of the allows reconstruction of digital data when small aluminum layer (also known as laser rot) errors or losses occur, making perfect copying • Natural aging possible. Since CDs vary little over time (until they fail), they may be duplicated without Standard CD Construction generational loss of information. Many CDs include a lacquer for durability, CD Life Expectancies a reflective layer (usually aluminum; sometimes more stable gold), dyes (most CDs are complex laminate structures vulnerable frequently organic), and a substrate to damage by light , humidity, temperature, ( often polycarbonate plastic, sometimes metal mishandling, and pressure. Since CD or etched glass) onto which the signals are information is stored in blocks of data with etched by laser light. A marking agent, such EDAC correcting codes it isn't easy to determine as ink or an ink printed label, may be placed when a CD is about to fail. CDs can be on the CD. Many of these materials, destroyed in a few minutes through poor particularly the substrate, vary over time handling or damaged from a few hours of being and by manufacturer. stored outside of their jewel cases. Types of CDs Storage or handling that would not destroy tape or paper, such as bending, pressure, or light There are many CD technologies. The exposure, can destroy a CD. Don't count on following are some of the most common CDs to last many decades because the types: polycarbonate substrate used on most CDs has a • Write-Once, Read-Many Times (WORM) shorter life than paper or film. Few companies format CDs are standard CDs commercially warranty their discs for more than a decade. produced that may contain text, images , Don't expect CD playback equipment for today's video, software, or sound. CDs to be available in 20 years, so equipment • Compact-Disc-Digital Audio (CD-DA) is (and where appropriate, software) maintenance is almost identical to standard WORM format essential. Don't dispose of your paper or film CDs. CD-DAs are produced commercially originals when using CDs for access copies. for the popular music market. National Park Service Conserve O Gram 19119 • Recordable Compact Discs (CD-R) are Where to Find Guidance WORM format CDs that are produced one-by one non-commercially by a recording disc Don't get your preservation data from vendors. drive. CD-Rs are playable on standard CD In the past vendors have often not disclosed DA or CD-ROM players. when their products were non-archival or short • Rewritable CDs can be erased and used again lived. Watch for media production, storage, like magnetic media. Available in 90mm and housing, and player standards from the 130mm digital optical formats, rewritable CDs American National Standards Institute (ANSI) require special players. Rewritable CDs use and the Association for Information and Imaging two separate technologies: Management (AIIM) and recommendations and 1. Magnetic-Optical Rewritable CD-MO uses manuals from non-profit professional heat and magnetic fields to write the CD. associations , such as the American Institute of Non-standard CD-MO players use Conservators (AIC) or the Society of American polarized laser beams that indicate the Archivists (SAA ). magnetic orientation of each spot. 2. Phase Change CDs use laser heat to The chart on pages 3 and 4 provides guidance change the media recording area from for preservation of archival CDs. metallic to crystalline, thus changing the reflectivity of the recorded section Sources Evaluation of CD Materials 3M Software Media and CD-ROM Services Bldg. 544-2N-01, 1185 Wolters Blvd . Look for CDs with a scratch resistant lacquer for Vadnais Heights , MN 55110 urability, a gold reflector layer, thalocyamine (612) 733-1110 yes, and a stable glass substrate. For these iscs, manufacturers quote life expectancies Digipress SA quivalent to paper and microfilm records; 18 Rue Bailey owever, testing data is incomplete. Don't use 14050 CAEN Cedex, France Ds made with cyamine dyes because they are Fax (43) 31-47-25-02 ess light stable. CDs with aluminum reflection ayers are more vulnerable to destruction due to Writable and Photo CD, Eastman Kodak xidation (caused by excessive humidity coupled 460 Buffalo Road ith airborne contaminants). Rochester, NY 14652-3834 (800) 235-6325 Most Durable CDs CD Computer Aided Test System According to conservators, such as William CDCATS 5A3 Nugent (see References), the following are the Advanced Audio Development USA, Inc. most durable CDs: 5335 Merle Hay Road, Suite 9 • Super CD Johnstown, IA 50131 • Kodak Writable CD (515) 254-9494 • Kodak Photo CD • Digipress Century Disc Gold Compact Disc Inspection System • Digipress Century-Disc Ark Automatic Inspection Devices, Inc. • Digipress Century-Disc Eon P.O. Box 6295 Toledo, OH 43614 (419) 536-2793 2 Care of Archival Compact Discs Conserve O Gram 19119 National Park Service To Preserve Your Archival CDs Do This ... Don't Do This .•. Environment • Store and use CDs at 10-20°C (50-68°F) and 40-50% RH, • Don't store CDs near heat sources, away from sudden changes in temperature and relative including the heat of ultraviolet light. humidity. Poor temperature and humidity in CD storage and Heat can•cause• the different layers of usage spaces may lead to warpage of the substrace and a ihe CD to delamiriate or can cause resulting lack of CD flatness. CDs that aren't flat won't birefringence, the double bending of track, making them unplayable. light This optical effect leads to • Store CDs in dark storage. Ultraviolet light, including reduced signal strength and disc sunlight, can cause the polycarbonate substrate or the errors or failure. scratch-resistant layer to darken, leading to player • Don'n-tore CDs in high humidities misreading and mistracking. because this may cause oxidation of • Store CDs in an air-conditioned space because polycarbonate the reflective layer. substrates can absorb moisture and react to heat. These reactions in the substrate or the reflective layer can make the CDs unplayable. Housing CDs Do This. Don't Do This. • House CDs in jewel cases with an internal tray and hub to • Don't use cracked or broken jewel hold the CD in position. If software, the CD may be housed cases; replace them with new ones. in paper sleeves. Polystyrene jewel cases are the preferred • Don't house CDs next co acidic paper, storage system, although paper or board housing that is inks,. or adhesives. certifiably acid-free is acceptable as long as it is boxed • Don't mark CDs with adhesive labels, vertically in archival boxes. ink, graphite,• or similar materials; • Replace the jewel cases that have no internal tray or hub instead, label their Jewel cases. with ones that do. An ink-printed paper label may be fitted • -Don't label CDs by writing directly under the tray for reading through the jewel case cover. For upon. either the CD or a pressure long-term storage, remove any booklets, notes, or unadhered sensitive label that is already applied printed paper labels in the jewel case because they may be to the -CD surface_because thismay acidic. Key these items to the CD catalog number and lead to delamination . house them in archival storage. • Don't pun pressure sensitive tape or labels off CDs because this may lead to delamination Storing CDs Do This. Don't Do This. • Select storage systems that protect CDs from excessive or • Don't tuck CDs into long term cycling heat and cold, ultraviolet light exposure, air storage permanently. Check CDs for pollution, and scratching by dust or handling. delamination and information loss at • Store CDs and other optical discs vertically within their yearly intervals. See Sources above jewel cases in slotted racks or boxes, unless the CDs are • Don't use CDs for long .term storage played on a regular (daily) basis. CDs being played withoutkeeping atleast two copies. of regularly should be housed in CD caddies. Caddies are any hardware. or software.necessary polystyrene or acrylonitrile-butadiene-styrene (ABS) for access. _ protective holders that contain many CDs for juke boxes € Don't allow CDs to lean within their or player auto-changers. storage systems; keep them upright. Care of Archival Compact Discs 3 National Park Service Conserve O Gram 19/19 To Preserve Your Archival CDs Do This ... Don't Do This. Handling and Use • Wear clean, white cotton (lint-free) gloves when handling • Don't use the only copy of a CD CDs. created for long.term data storage: • Hold the CD by the edges. Never flex, bend, or place • Don't mark, label, or emboss a CD pressure on a CD because this may cause delamination. € Don't ship original orsole copy CDs. • Hand deliver original CDs rather than shipping them. • Don't use UPS, the mail,or publi • Write on CD labels before applying them. If the CD is carriersto transport sole copyCDs already labeled, add additional labeling to the CD housing. • Don't expose recordable CDsto light • Avoid rough handling of CDs.

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