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Preservation

Handling of sound carriers - Practical suggestions

Remarks on discs

"Acetates"

This type of disc was commonly used for instant recordings before being replaced by the magnetic wire or tape. It was conceived as a compromise offering facility of recording and reproduction, but this advantage was offset by negative effects on the long-term preservation of the carrier. The composition of these discs has changed considerably over the years, progressing from wax to ethylcellulose, to acetylcellulose and, lastly, to nitrocellulose.

The shellac disc

Shellac, or an equivalent material, was used for pressing 78rpm discs with a normal groove (lateral or vertical cutting). In this case too, there were different construction processes, but these carriers also were characterized by their variable duration over time.

The plastic disc

As long-playing discs, or microgroove discs, are composed almost exclusively of synthetic material, they cannot be considered as a mere improvement of shellac discs. They are made of polyvinylchloride (PVC) or polystyrene. The most important agents causing chemical degradation of PVC discs are exposure to ultraviolet rays (UV) and heat. For polystyrene discs, instead, there is a risk of oxidation.

The optical disc

The optical disc is decidedly the most stable of all the discs considered so far. Normally, it consists of a base of transparent polycarbonate. The information is recorded on the upper surface of this material. This face is then covered with a thin reflecting metallic layer and, in turn, this is covered with a layer of protective lacquer on which the label is printed. The most interesting element of this construction technique is that the surface of the disc is physically separated from the surface on which the information is recorded, so the precise focusing of the latter makes the presence of any anomalies (dirt, scratches, ...) on the disc irrelevant.

The magneto-optical disc

In this context, it is necessary to mention also magneto-optical discs. Used originally in the computer world to store data, they have increasingly lost importance with the dramatic increase of capacity of the hard disc (HDD). They continue to survive in the commercial world in the (re-writable) MiniDisc format.

 

Remarks on tapes

The magnetic tape was introduced immediately after the Second World War. By 1950, its degree of reliability was such that it completely replaced the acetate disc for direct recordings.

Each magnetic tape (reel or cassette, audio or video) consists of a carriering base (paper, acetylcellulose, PVC, PET, ...) onto which is fixed a layer of magnetic particles (Fe3O4, Fe2O3, CrO2, ...). From the structural standpoint, it is therefore exposed to the same risks as other sound carriers, with some additions characterized by the shape and the particular system of recording and reproduction.

 

Causes of deterioration

Environmental conditions

The most important alterations in the structure of an audio carrier are the internal reactions normally caused by the prevailing environmental conditions. The physical and chemical properties of a resin may be altered by various factors. These structural changes are caused by:

Further causes of deterioration, specific to tapes, are:

Mycosis, formation of mold

If we go back in time, we observe a more intensive use of organic materials, especially in the field of additives, which also offered a high potential nutrient capacity for fungi. Nowadays, a possible source of nourishment for these organisms is the fat deposited by the hands or other parts of the human body. The damage caused by fungi, contrary to what is generally thought, also extends to materials that are not in themselves nutrients. In fact, the digestion of their food takes place externally with the secretion of enzymes and acids that can have negative effects on any material.

Incorrect handling

In this case, reference is made to daily use, storage, transport, etc.

 

Important points to be remembered

For mechanical cut discs

For optical discs

 

Recommendations

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