The second step in a preservation strategy is to make sure that the storage environment is appropriate for the electronic media in the collection. In general, the storage environment should have a relative humidity (RH) below 50% and be cool enough for all types of media.
Optimal environmental storage conditions
Optical media require:
In addition, it is important to avoid large, rapid fluctuations in temperature and RH because these changes can promote delamination of disc layers, especially on discs that are poorly manufactured.
Optimal physical storage
Best storage cases CDs and DVDs should be stored in standard polystyrene plastic “jewel” cases that are 10 mm (3/8 in.) thick. For more durability, store the items in standard-thickness polypropylene cases (shown in the photograph).
Cases vs. sleeves Do not use plastic or paper sleeves because these:
How to store CD and DVD cases Store the jewel cases:
Standard commercial CDs and DVDs are not sensitive to light. However, CD-Rs and DVD-Rs may contain light-sensitive dyes as recording material.
Labelling Label disc media on the clear inner hub area using a water-based permanent ink felt tip marker. Avoid other labelling methods, especially stick-on labels.
Magnetic tape media require:
Degradation problems
Binder layer degradation — description The binder layer of magnetic tapes can suffer chemical degradation. The binder layer is a polymer that holds the magnetic particles onto the plastic tape base. Certain polymer formulations are more susceptible to degradation than others. Tapes that degrade in this fashion become sticky and lose magnetic material, eventually becoming unplayable.
Open-reel audiotapes tend to have this problem more than other formats, although it is a concern with all tape formats.
How to deter binder layer degradation Cool, dry storage will slow the chemical degradation process and allow more time before action needs to be taken. If tapes show evidence of deterioration, the information they contain should be transferred to new media formats. Note that the degraded tapes will probably need to be treated to make them playable before the transfer can occur.
For more information, see CCI’s range of Technical Bulletins, including TB #27 Remedies for Deteriorated or Damaged Modern Information Carriers.
“Vinegar” syndrome degradation — description Many early audio reel-to-reel tapes (1935–1970) used cellulose acetate as the plastic support or base layer. The acetate plastic in these tapes is subject to acid-catalysed hydrolysis that leads to breakdown of the polymer chains in the base layer. This degradation gives off acetic acid (the same acid that gives vinegar its characteristic smell), and is known as “vinegar” syndrome.
When an acetate tape degrades, the base shrinks, distorts, and becomes brittle — which makes it difficult to play the tape. Information on the degraded tape should be transferred to another suitable medium as quickly as possible.
How to deter vinegar syndrome degradation Cool and dry storage will significantly slow down the chemical degradation of acetate-based magnetic tapes.
Separate any tapes that smell of vinegar from the rest of the collection, and keep them in a well-ventilated area. They should never be returned to the general collection storage area because they pose a threat to other materials.
Store away from magnetic fields Magnetic (audio and video) tapes and magnetic disks should be stored at least 7.6 cm (3 in.) away from a magnetic field such as might arise from electrical wiring or electrical equipment.
Store cases on edge Magnetic tape reels should be stored on their edges in the same manner as CDs and DVDs.
Storage containers for open reels and cassettes should preferably:
Cases for heavier reels should support the reel at the hub.
For lighter reels, such as those for ¼-in. audiotapes and for VHS cassettes, paper boxes have often been used. These boxes are acceptable if they meet the following conditions:
Check tension of the tape on the reel The quality of the audiotape or videotape “pack” (or tape “wind”) is a major determinant in whether the tape will be physically damaged, warped, or deformed. Tapes that are too loosely or too tightly wound on the reel, or have edges projecting from the tape pack, should be rewound.
How to rewind magnetic tape on reels If a tape requires rewinding, perform the procedure with care. Done incorrectly, rewinding may actually cause more damage to the tape than if it was left alone.
Surveying the electronic media collection will identify the items that need to be reformatted — Step 3.
