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Care and Handling of Alternative Media
Charlotte Payne and Wendy Jones have compiled this information from a multitude of current preservation and scientific sources. Because of the nature of the media and the lack of a viable, long-term strategy to ensure that digital information will be readable into the future, this information is subject to frequent revision. As Jeff Rothenberg stated in his report, "Avoiding Technological Quicksand: Finding a viable foundation for digital preservation" (CLIR, January 1999), "The long-term digital preservation problem calls for a long-lived solution that does not require continual heroic effort or repeated invention of new approaches every time formats, software or hardware paradigms, document types, or recordkeeping practices change. The approach must be extensible, since we cannot predict future changes, and it must not require labor-intensive translation or examination of individual documents. It must handle current and future documents of unknown type in a uniform way, while being capable of evolving as necessary. Furthermore, it should allow flexible choices and tradeoffs among priorities such as access, fidelity, and ease of document management." In the meantime, we make the following recommendations.
- Use high quality media and devices
- Minimize handling and use of archival media and/or record number of accesses and implement appropriate refreshing
- Write archival copies from different devices and software
- Make archival copies to comparable media purchased from different suppliers
- Do not touch magnetic recording surface
- Do not allow unauthorized use of digital media
- Annually read a sampling of the digital information to detect any degradation
- Periodically rewind tapes at constant tension, at normal tape speed
- Do not use video tape rewinders
- When in doubt, make a copy
- Be sure the machine works before you insert a tape
- Transport magnetic media in enclosures with space clearances of 50mm
- Know what type of machine the tape was recorded on and keep the machine
- Copy the information on magnetic media every 6-7 years to refresh the data and allow for any necessary media migration
- Inspect and verify all copies. Label all copies. Don't use system backup tapes as preservation masters
- Archival storage copy of audio material should be on 1.5 mil mylar tape only
- Use mastering grade tape for original recordings and archival copies
- Copy important archival computer data to new disks or tapes every 5-7 years, converting the data into a form that can be read by current programs
- Back up magnetic media onto longer-lived media (choose PET [polyethylene terephthalate] or Mylar brand) tapes with iron oxide pigments, not metal particulate (mp) or chromium dioxide pigments. Use reel-to-reel tapes rather than cassettes for master copies.
- Take care not to drop magnetic media; keep 3" away from magnetic fields
- Rewind cases of bad packing or buckling when discovered
- Produce 3 copies for all magnetic media; recopy every five years; store copies separately. Inspect and verify all copies. Label all copies. Don't use system backup tapes as preservation masters
- Maintain playback equipment in perfect condition; clean regularly
- Maintain current versions of software and transfer media as necessary
- Keep storage area free of smoke, dust, dirt and other contaminants
- Store magnetic media away from strong magnetic fields
- Store in a cool, dry, stable and secure environment
- Store in a dust-free environment
- Store at a constant temperature between 62F and 70F and at a constant humidity between 30% and 45%; acclimatize media before use, if necessary
- Store away from direct sunlight
- Maintain proper ventilation and air circulation to avoid microclimates
- Keep rooms where media are stored clean. Vacuum often. No food or drinks in area. Use filters on AC equipment. Clean equipment such as tape decks or disk drives regularly
- Store disks, cassettes and boxes of tape reels vertically and provide vertical supports every 4 to 6 inches. Supports should not be smaller than the container
- Do not pack too tightly Store each size medium separately
- Keep sound recordings in dark storage. Fit light fixtures with fluorescent tubes which do not produce UV radiation in excess of 75 microwatts per lumen
- Enclose media in a sleeve or box made of archival quality materials such as acid-free paper, paperboard, paperboard-plastic laminate, or inert plastics such as polyethylene, polyester or polycarbonate
- Do not leave items out of their containers
D3 Magnetic Tape
- 50 yrs at 50F, 25%RH
- 25 yrs at 59F, 30%RH
- 15 yrs at 68F, 40%RH
- 3 yrs at 77F, 25%RH
DLT Magnetic Tape
- 75 yrs at 50F, 25%RH
- 45 yrs at 59F, 30%RH
- 15 yrs at 68F, 40%RH
- 3 yrs at 77F, 25%RH
- 75 yrs at 50F, 25%RH
- 45 yrs at 59F, 30%RH
- 20 yrs at 68F, 40%RH
- 10 yrs at 77F, 25%RH
- 30 yrs at 50F, 25%RH
- 15 yrs at 59F, 30%RH
- 3 yrs at 68F, 40%RH
- 9 mos. at 77F, 25%RH
Magnetic media are tapes (reels, cartridges and cassettes) and disks (hard disks, floppy disks) which utilize magnetic properties of metallic materials suspended in a non-magnetic mixture on a substrate or backing material. From 1935-1960s, tapes were made from heavily plasticized cellulose acetate. In the early 1960s, a type of polyester material called polyethylene terephthalate was used. DuPont's Mylar brand is the most widely used tape. Magnetic media fail because of tape curl; high friction due to tape stickiness; tape adhesion failure; tape cohesion failure; and head build-up. Acetate tapes become brittle due to loss of plasticizer; polyester is more stable and degrades at a slower rate. Better grades of polyester tape have been tensilized, but can permanently stretch out of shape. The base layer for floppies is also polyester, although it is thicker than that used for tapes. The base layer for most hard disks, fixed or removable, is one or more aluminum or glass platters.
The binder layer is a mixture of plastic resin, magnetic particles, solvents, wetting agents, plasticizers, antioxidants, lubricants, mineral powders, fungicides and, sometimes, conductive particles. These ingredients determine the properties of the layer, including its flexibility, uniformity of composition, friction against the heads, abrasion resistance, static charge dissipation, and adhesion to the substrate and mold resistance. The binder systems used in today's audio and videotapes are generally based on polyester polyurethanes. These polymers degrade by a process known as hydrolysis, where the polyester linkage is broken by a reaction with water. One of the by-products of these degradations is organic acids. These acids accelerate the rate of hydrolytic decomposition; the acids can also attack and degrade the magnetic particles. Tapes can become too sticky to play as a result of an overabundance of hydrolysis products. They can fail due to a loss in the magnetic signal as a result of a decrease in magnetic remanence or coercivity. They can fail because the magnetic coating has failed to adhere to the tape backing, or due to irreversible shrinkage of the substrate. Tapes are also subject to mechanical stresses, abrasion and scratching.
The lifetime of a tape is defined as the length of time a tape can be archived until it will fail to perform. LE (life expectancy) of magnetic media is largely undocumented; according to manufacturers, thirty years appears to be the upper limit for magnetic tape products, including video and audiotapes. Some gold plated/glass substrate digital optical disk technologies promise 100-year lifetimes; this may be irrelevant when the system technology may be in use for only 10-20 years. To truly achieve a lengthy archival life, recording systems, spare parts and technical manuals would need to be archived with the recorded media. Tapes that are frequently accessed may have a reduced life expectancy due to wear and tear. The more a tape or cassette is handled, the more it is contaminated with fingerprints and debris. Because of potential damage to the tape, it is important that the tapes are inserted and ejected at areas of tape that contain no recorded information.
General Guidelines for Magnetic Media
- Handling and use should be minimized to reduce wear
- Media should be of high quality from reputable suppliers
- Archive copies should be made to guard against faults
- Drives should be of good quality and well maintained
- Tape should be handled only in no smoking, no food, clean areas
- Avoid contamination of the tape by dirt, dust, fingerprints, food, cigarette smoke and ash and airborne pollutants
- Do not let tape or leader ends trail on the floor
- Do not drop or subject to sudden shock
- Don't expose to sun, heat or excess moisture
- Store open reel and cassette tapes with the reels or tape pack vertical and supported by the hub
- Use high quality reels, cassettes and containers
- Return tapes to containers when not in use
- Cut off damaged tape or leader/trailer ends from open reel tapes
- For open-reel tapes, use protective collars
- Do not use general purpose adhesive tapes to secure the tape end or for splicing
- Minimize handling
- Do not touch the tape surface or the edge of the tape pack unless absolutely necessary and then wear lint-free gloves
- Clear the recorder tape path thoroughly at the recommended intervals
- Discard tapes with scratches or any other surface damage because it causes debris to be left in the recorder tape path
- Tape is least vulnerable to damage when wound in a smooth, even pack
- Rewind tape at an interval of not more than 3 years. This relieves tape pack stresses and provides early warning of any problems
Audiotapes are preserved by re-recording original recordings onto reel-to-reel tape, following nationally recognized preservation practices and guidelines. Analog copies properly stored are considered to be the best medium for long-term preservation of sound recordings.
Digital copies are the better option for access and use. CDs suffer less from wear and tear during use than reel-to-reel or cassette tapes. High quality CD-Rs are a stable medium with a good life expectancy.
Digital video formats are compressed and use very thin base films
Compression methods degrade quality of video
D5 and D6 are uncompressed digital videotape formats but machines very expensive ($80K)
Mixing formats with different compression techniques degrades video quality; stay with one type of compression technique
Storage guidelines for videotapes:
- Keep in cool, relatively dry environment (60-73F and RH 20-30%). Avoid fluctuations (no more than 7F)
- Monitor storage environment with hygrothermograph
- Store tapes on metal shelves, preferably grounded. If shelves are motorized, store tapes away from motors. Store tapes upright and allow for air circulation. Don't store near magnetic fields created by motors, generators, television sets, elevators, headphones, speakers, microphones or magnets. Store duplicates and high quality masters in different locations.
- Protect against accidental erasure by removing the record tabs
- Avoid contamination of tape surface. Touch open reel tapes by beginning and end only. Wash hands and use gloves.
- After use, rewind to the end; don't store a tape that is stopped in the middle. Rewinding means you fast-forward the tape all the way to the end.
- Use high quality, brand name tapes for copying and remastering
- Label minimally and with proper materials. Use archival labels which are non-acidic and which adhere without peeling off
- Use appropriate tape containers (strong and stable; resistant to dirt, dust and water; inert; able to be closed and latched securely)
- If you ship tapes, be sure they are double-boxed, with space between tape cases and exterior boxes. Use safe packaging materials, not fiber-filled mailers. For tapes in preservation storage: 50F and 30%RH
- Keep storage and playback areas free from dust and other contaminants
- Protect tapes from liquid, light and heat and erasure Store in their cases Don't rewind after playing. Rewind just before playing.
- From LC: materials to be preserved for a minimum of 10 years: store at 65-70F, 45-50% RH
- Materials having permanent value: 45-50F, 20-30% RH for magnetic tapes (open reel and cassette) and 45-50% RH for all others. Keep away from UV
- Videotapes will deteriorate over time. Store away from magnetic and electrical fields. Handle only by their cassettes. Don't use fast forward or fast reverse on playback equipment.
Optical storage media (CDs, DVDs) use laser light to read from a data layer. They are complex laminate structures vulnerable to damage by light, humidity, temperature, mishandling and pressure. Most CDs fail because of physical stress leading to delamination, warping, and/or improper tracking; dirt or grit scratching media and leading to losses of information; yellowing of the plastic or light recording layer; low reflectivity due to oxidation of the aluminum layer (laser rot) and natural aging. CD-Rs are less stable than CD-ROMs. Because device reader is not in contact with disk, mechanical failure is less likely to lead to data loss than damage to the disk itself through poor handling or storage. Media should be refreshed on a regular cycle. Generic figures for lifetime of media under various temperature and humidity levels assuming optimal use (no or infrequent access) and environmental conditions (stable and free of contaminants, UV light and strong magnetic fields) are:
- 75 yrs at 50F, 25%RH
- 45 yrs at 59F, 30%RH
- 20 yrs at 68F, 40%RH
- 10 yrs at 77F, 25%RH
According to the NAL
- Temperature should be between 62.6 and 68F
- Humidity should be between 30 and 40%
- Temperature and humidity should remain constant
- There should be no airborne particulate matter
- There should be no airborne gases, including ozone and organic compounds
- Storage on untreated wooden shelves should be avoided
- Storage areas should be free of smoke and food
- Materials should be stored upright
- Staff should be trained in the proper techniques of handling (use white lintless cotton gloves)
Optical disks and their associated electronic media are extremely fragile compared to paper. In order to protect and preserve these formats, the library should establish two areas, one for user services and one for archival storage. Provide good containers or enclosures for CDs. Cheap plastic sleeves, such as those found in the backs of books are not suitable for long-term storage. Jewel cases are good protection against scratches, dust, light and rapid changes in humidity. Spacer cards should be retained. Make sure the material is acid-free. Protect the individually cased CDs further by placing them in a closed box, drawer, or cabinet.
User-applied labels of any kind may unbalance the CD and make it difficult for the player to read. Labels may peel in humid conditions. Once on the CD, it is important not to try and remove it. If it is necessary to write on the top side of a CD, a soft felt-tip marker is preferable, but with some solvent-based markers there may be a danger of the solvents migrating into the protective lacquer. Always follow the disk manufacturer's instructions.
To clean a CD, use distilled water or Kodak lens cleaner and a lens tissue. Always wipe from the center hub toward the outside edge.
Other Recommendations Include
- Store CDs in dark storage. UV light, including sunlight can cause the polycarbonate substrate or the scratch-resistant layer to darker, leading to player misreading and mistracking.
- House CDs in jewel cases with an internal tray and hub to hold the CD in position. If software, the CD may be housed in paper sleeves. Polystyrene jewel cases are the preferred storage system, although paper or board housing that is acid-free is acceptable as long as it is boxed vertically in archival boxes.
- Don't use cracked or broken jewel cases
- Don't house CDs next to acidic paper, inks or adhesives
- Replace the jewel cases that have no internal tray or hub with those that do. An ink-printed paper label may be fitted under the tray for reading through the jewel case cover. For long-term storage, remove any booklets, notes or unadhered printed paper labels in the jewel case because they may be acidic. Key these items to the CD catalog number and house them in archival storage.
- Don't mark CDs with adhesive labels, ink, graphite or similar materials; instead, label their jewel cases.
- Don't label CDs by writing directly upon either the CD or a pressure sensitive label that is already applied to the CD surface because this may lead to delamination
- Don't pull pressure sensitive tape or labels off CDs because this may lead to delamination
- Select storage systems that protect CDs from excessive or cycling head and cold, UV light exposure, air pollution, and scratching by dust or handling.
- Store CDs and other optical disks vertically within their jewel cases in slotted racks or boxes unless the CDs are played on a daily basis. CDs being played regularly should be housed in CD caddies. Caddies are polystyrene or acrylonitrile-butadiene-styrene (ABS) protective holders that contain many CDs for jukeboxes or player auto-changers.
- Check CDs for delamination and information loss at yearly intervals
- Don't use CDs for long term storage without keeping at least two copies of any hardware or software necessary for access
- Don't allow CDs to lean within their storage systems; keep them upright
- Don't use the only copy of a CD created for long-term data storage
- Wear clean, white cotton (lint-free) gloves when handling CDs
- Hold the CD by the edges. Never flex, bend, or place pressure on a CD because this may cause delamination
- Hand deliver original CDs rather than shipping them
- Write on CD labels before applying them. If the CD is already labeled, add additional labeling to the housing
- Avoid rough handling of CDs. CDs play from the center to the outer edge. When a tracking problem exists, it is usually due to warpage, scratches, or delamination from improper handling
- Clean CDs only when absolutely necessary
- Use compressed air for cleaning. If compressed air doesn't work, dampen a cloth with distilled water and brush the CD to the outer edge from the center of the disk.
- Test CDs regularly so you know when to implement the plan. Ensure that the contractor uses an EDAC technology system when copying CDs. EDAC incorporates mathematical formulas that ensure redundancy so that small sections of digital data can be reconstructed if lost or damaged. EDAC systems require almost 25% additional storage space on your new copy CD. Copying CDs is a slow and expensive job.
- Set up an inspection process for CDs remastered or recopied prior to payment for the work.
- Don't use CDs for long-term storage of data without setting up a data migration and remastering schedule.