By Gilles St-Laurent
Music Division
National Library Of Canada January 1996

Sound recordings are machine readable artifacts; they are documents for which the integrity of the information they contain is directly related to the artifacts' physical well being. Since the majority of sound recordings are made of plastic, conservation must be treated as a plastics degradation problem, requiring a different approach than paper conservation. It is important to understand the basic chemical degenerative processes and the principles of the retention of sound by the various media in order to ensure that proper action is taken to slow the rate of degradation.

VINYL DISCS

Thus far, vinyl has proven to be the most stable of the materials that have been used in the manufacture of sound recordings.

However, although stable, its life is not indefinite. Pickett and Lemcoe, in Preservation and Storage of Sound Recordings, states that "failure by chemical degradation of a vinyl disc in ordinary library environments should not occur in less than a century".

Vinyl discs are made of polyvinyl chloride (PVC) and a small percentage (usually less than 25 percent) of "fillers", stabilizer, pigment, anti-static substances, etc. Internal plasticization, through a copolymerizing of vinyl acetate with vinyl chloride, is needed to achieve the required properties for the desired application. Polyvinyl chloride degrades chemically when exposed to ultraviolet light or to heat. Phonograph discs are exposed to high temperatures during moulding and pressing. Unless stopped, this heat would be a catalyst for ongoing dehydrochlorination, which is the release of hydrochloric acid (HCl) from the PVC as a result of thermo-degradation. Stabilization is therefore achieved by adding a chemical to the resin during manufacture. This does not prevent the degradation but controls it, mainly by consuming the free HCl. Sufficient effective stabilizer remains in a plastic phonograph disc to protect it for several decades after pressing.

PRESERVATION OF SOUND RECORDINGS

A good definition of preservation put forward by the International Institute for Conservation--Canadian Group and the Canadian Association of Professional Conservators is that preservation encompasses "all actions taken to retard deterioration of, or to prevent damage to, cultural property. Preservation involves controlling the environment and conditions of use, and may include treatment in order to maintain a cultural property, as nearly as possible, in an unchanging state."

There are essentially only three concerns to consider when handling and storing sound recordings:

that they be kept free of any foreign matter deposits;
that they be kept free of any pressure that might cause deformations; and
that they be stored in a stable, controlled environment.

FOREIGN MATTER DEPOSITS

General

Dirt can be classified into two categories: (1) Foreign matter depositswhich are not part of the original object, such as grease from fingerprints, soot, stains, adhesives, etc. and (2) alterations of original object material through chemical reactions (whether internal reactions or reactions with environmental agents). Metal corrosion products, palmitic acid from acetate discs, or a gummy substance on tapes are examples of alteration in the state of the original.

Dust is commonly a mixture of fragments of human skin, minute particles of mineral or plant material, textile fibres, industrial smoke, grease from fingerprints, and other organic and inorganic materials. There are often salts such as sodium chloride (carried in from sea spray or on skin fragments), and sharp gritty silica crystals. In this chemical mixture are the spore of countless moulds, fungi and micro-organisms which live on the organic material in the dust (fingerprints, for example, serve as good culture media). Much of the dirt is hygroscopic (water-attracting) and this tendency can encourage the growth of moulds, as well as increase the corrosiveness of salts, hydrolysis and the release of acids.

Dust (including fingerprints) will negatively affect sound recording preservation in a number of ways:

Discs

Dust is abrasive, and combined with the pressure exerted on the groove walls by the stylus, can permanently etch the walls worse, dust can also be imbedded permanently into thermoplastic substances. Only a small point of the stylus is actually making contact with the groove walls. One and a half grams of stylus pressure on such a minute surface translates to several tons of pressure per square inch. The resulting drag generates enough heat that the plastic partially melts (though not enough to deform), causing a microscopic flow around the stylus into which dust can be embedded permanently. To minimize foreign matter deposits:

General:

Never touch the surface of a recording. Use clean, white lintless cotton gloves and handle by the edges.
Recordings should not, unnecessarily, be left exposed to open air. Return items to their containers when not in use and never leave storage containers open.
Do not place recordings near sources of dust including paper or cardboard dust.
Keep the surrounding area clean. Do not consume food or beverages in the area in which recordings are handled.
Keep storage facilities as clean and dust-free as possible.
The air conditioning system should be equipped with dust filtering equipment.
Keep labelling to a minimum, but limit the placement of labels, especially pressure sensitive labels, to the container using conservation ink.
Keep equipment clean, well adjusted and in good working condition.

Grooved discs

Do not use paper or cardboard inner sleeves and do not store records without inner sleeves.
Use soft polyethylene inner sleeves. Do not use record sleeves made of PVC.
Remove grooved discs from the jacket (with the inner sleeve) by bowing the jacket open by holding it against the body and applying a slight pressure with a hand. Pull the disc out by holding a corner of the inner sleeve. Avoid pressing down onto the disc with the fingers as any dust caught between the sleeve and the disc will be pressed into the grooves.
Remove grooved discs from the inner sleeve by bowing the inner sleeve and letting it slip gradually into an open hand so that the edge falls on the inside of the thumb knuckle. The middle finger should reach for the centre label. Never reach into the sleeve.
To hold a disc, place the thumb on the edge of the disc, and the rest of the fingers of the same hand on the centre label for balance. Use both hands on the edge to place disc on turntable.

CLEANING

Since dust is usually held in place by electrostatic attraction, dry wiping on its own does not work effectively. The added friction created by the duster will cause the dust to jump back to the charged surface. Distilled water is used for cleaning records and CDs for many reasons. Its precise chemical makeup is known, it will not leave any residue behind, is safe to use, and is inexpensive. Water disperses static charges and counteracts the increase in conductivity from the pick-up of salt deposits from finger prints. However, water alone cannot dissolve grease, thus surfactants are used as additives to enable water to be a grease solvent. Surfactants break grease surface bonds and allow water to penetrate grease solids, causing swelling and then random dispersion.

General

The Canadian Conservation Institute (CCI) recommends the use of nonionic, ethelyne oxide condensates surfactants to clean sound recordings. The CCI does not foresee long-term problems associated with the use of nonionic surfactants such as Tergitol. Tergitol 15-S-3 is an oil soluble surfactant and 15-S-9 is a water soluble surfactant. Combined they remove a wide range of dirt and greases and can safely be used on sound recordings. Use 0.25 part of Tergitol 15-S-3 and 0.25 parts of Tergitol 15-S-9 per 100 parts of distilled water. (These products are available in small quantities from TALAS (Division of Technical Library Service Inc) 213 West 35th Street, New York, N.Y. (212) 465-8722.) The recording must then be rinsed thoroughly with distilled water to eliminate any trace of detergent residue.
Keep an airgun handy to blow off light surface dust.

Grooved discs

Grooved discs are best cleaned using a record cleaning machine such as the Keith Monks, VPI, Nitty Gritty using 0.25 part of Tergitol 15-S-3 and 0.25 parts of Tergitol 15-S-9 per 100 parts of distilled water. These machines allow for an even dispersion of fluid and can then vacuum the liquid leaving a clean, dry surface. The discs must then be rinsed thoroughly with distilled water and vacuumed dry to eliminate any trace of detergent residue. Records should be cleaned before each playback.
Clean Vulcanite discs showing signs of acid build up using 0.25 part of Tergitol 15-S-3 and 0.25 parts of Tergitol 15-S-9 per 100 parts of distilled water and rinse thoroughly.
Clean acetate discs showing signs of palmitic acid deposits (white greasy substance on acetate disc surface) as if cleaning LPs, except add 1 part ammonia per 100 to the Tergitol cleaning solution. Do not use ammonia on shellac based discs.

SURFACE DEFORMATIONS

Since the surface of a sound recording is the information carrier, it is critical that the surface be well cared for. Physical deformations such as warping of discs, stretching of tape or shock from dropping them, will directly affect sound information integrity. One must develop a respect for the integrity of the artifact. To minimize deformations

General

Never leave recordings near sources of heat or light (especially ultraviolet light) as plastics are adversely affected by both.
Do not place heavy objects on top of recordings. Recordings should never be placed on top of each other.
Shelve recordings vertically; do not stack "off vertical" or horizontally.
Do not use shelving units where supports put more pressure on one area of the recording or where supports are more than four to six inches apart.
Do not interfile recordings of different sizes as smaller items may get lost or damaged, while larger items may be subjected to uneven pressure.

Discs

Remove shrink-wrap on LPs completely. Shrink-wrap can continue to shrink, thus warping the disc.

ENVIRONMENT

A proper environment for the storage of sound recording is essential to retard degradation mechanisms. Elevated temperature and humidity can affect certain chemical properties of the plastics that make up recording media and can also create an environment that encourages the growth of fungus. Wide or rapid fluctuations of the environment are equally detrimental to the long term preservation of sound artifacts.

Vinyl discs

Vinyl discs are adversely affected by ultraviolet light and thermal cycling (heat fluctuation). The consequence of thermal cycling is that each cycle of temperature results in a small irreversible deformation, and these deformations are cumulative.

Vinyl discs are resistant to fungal growth and are unaffected by high humidity levels.

Proper storage environment

Store recordings at a maintained temperature of between no more than 15-20°C. Fluctuation of temperature should not vary more than 2°C in a 24-hour period.
Maintain a relative humidity of 25-45%. Fluctuation of relative humidity should not vary more than 5% in a 24-hour period.
Maintain proper ventilation and air circulation of stacks at all times to avoid any micro climates.
Keep sound recordings in dark storage when not being consulted. Fit light fixtures with fluorescent tubes which do not produce ultraviolet radiation in excess of 75 µw/lm (microwatts per lumen).
Separate and isolate from tape vault acetate tapes exhibiting an acetic acid odour. Copy the tapes promptly.

CONCLUSION

Over the past century, recorded sound has become an intrinsic part of our culture. Upon hearing an early sound recording device in 1888, Sir Arthur Sullivan stated that he was "astonished and somewhat terrified at the result of this evening's experiments--astonished at the wonderful power you have developed, and terrified at the thought that so much hideous and bad music may be put on record forever."

Unfortunately, sound recordings are not "forever". These are ephemeral documents, both in their physical composition and consequently in the means by which the sound is ultimately retained. They can have their life span shortened considerably by both internal and external forces. By undertaking certain precautionary measures, custodians of the heritage of sound can lengthen considerably their collection's life span thus preserving a rich, invaluable world of sound.