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7.2 The care of grooved recordings

Gilles St. Laurent et al 1995

1. Introduction

Disc and cylinder recordings are machine readable artifacts; they are documents whose physical well being is essential to preserve the integrity of the information that they contain. Many recordings, particularly those not produced for the commercial market are of unique historic value and should be treated with great care.

Since the majority of sound recordings are made of polymers (commonly called plastics), conservation must be treated as a polymer degradation problem, requiring a different approach to that used for the conservation of paper. As with paper, the life expectancy of a disc or cylinder is finite. The processes of chemical degradation are at work in all existing forms of sound recording and cannot be stopped. The rate of degradation can, however, be speeded up by poor handling and storage of recordings.

To preserve sounds for longer than the life of the disc or cylinder, the material will have to be copied. This can be a complex task, particularly for older or fragile recordings. In particular, seek expert advice if the collection includes cylinders, instantaneous (acetate) discs or any discs showing physical signs of decay. The basic message to remember is "If in any doubt, get advice". It is easy to damage these recordings but very difficult to restore them.

2. History of Cylinders and Discs

The first known sound recording was made by Thomas Alva Edison in 1876 using a sheet of tin-foil wrapped tightly around a cylindrical metal former with the basic groove pattern cut into it. The cylinder was turned by hand and a stylus attached to a diaphragm at the end of a pickup horn indented the pattern of the sound waves into the tin-foil. Initially, Edison envisaged the cylinder recording being used primarily as a dictating machine. It was only later that the idea of mass producing prerecorded cylinders became commercially feasible. Cylinders were made until 1929 and were used both as a home and office recording system and, using prerecorded music, as a form of entertainment.

The development of the gramophone disc involved more people. Although Emil Berliner, a German immigrant to the United States of America, patented the idea in 1887, several other people had been working on the same concept. The earliest description was written in 1876, just before Edison's Phonograph recording, by the Frenchman, Charles Cros, who deposited a sealed envelope with the Academie de Sciences in Paris. This was almost identical to the patent obtained later by Berliner. Alexander Graham Bell, the inventor of the telephone, and his colleagues also developed a form of disc recording. The crucial developments of quieter, more crackle free recordings and of the clockwork motor were made by Eldridge Johnson in 1896-7.

The commercial use of gramophone discs started in 1894 with discs produced by Emil Berliner. The earliest players were manually driven; either by turning a handle or by a foot operated treadle. It was not until 1897 with the introduction of quieter recordings and the clockwork driven machines that the gramophone became popular. From the start, the gramophone disc was used to distribute prerecorded music and songs. Although disc recording machines were made, they were primarily aimed at the professional market and not the home or the office.

3. How Sounds Are Recorded And Played Back

All grooved recordings physically retain information in the same fashion and are recorded in a similar manner. Acoustic recordings, (made prior to the use of microphones, ca. 1925), recorded sound by capturing and channelling changes of air pressure through a horn to a diaphragm with a cutting stylus mounted on it. The diaphragm would transform the changes of air pressure into a analogous mechanical motion while the cutting stylus etched the groove. Similarly, with the more modern electrical recordings, when the voltage generated by the microphone (which transforms changes in air pressure into changes in electricity) is applied to the cutting stylus, the stylus is moved in one direction when the voltage is increased and in the opposite direction when the voltage is decreased.

Cylinders and early Edison discs move the stylus vertically (hill-and-dale) and not from side-to-side (laterally) as with other discs. Examples of coarse groove discs that play from the centre outwards can also be found.

To retrieve information from a disc, a stylus is used to track the groove. The cartridge will convert the movement of the stylus to an electrical voltage (in the same fashion that a microphone converts mechanical motions to an electrical voltage) that can then be amplified and used to drive speakers. The movement of the speaker will be parallel to the movement of the stylus.

To play a cylinder, it first has to be mounted on the mandrel of a phonograph. Many cylinders have distorted central mounting holes and can easily crack if placed on a mandrel. The recording surface is very soft and, unless a modern, lightweight pickup is used, the recorded information can easily be scraped off by the playback stylus.

Careful examination of all old recordings is strongly advised before attempting to play them. If there is any visible sign of decay, seek expert advice. It is strongly recommended that cylinders and instantaneous discs be only played by an expert using a modern machine. If regular access to a collection of old recordings is required, then tape or CD-R copies should be made to avoid unnecessary playing of the fragile originals.

4. The Chemical Degradation Mechanisms Of Grooved Recordings

4.1 General

The life-span of a polymer is largely determined at the manufacturing stage. Variables such as basic resin, the materials added to the basic resin to alter its properties, the lamination of materials with dissimilar properties, and the manufacturing process itself, all directly affect the life-span of the polymer. Post-manufacture environmental factors such as storage conditions, temperature, humidity, and handling also contribute to the long-term stability of the polymers.

Polymers can be divided into two main classes: thermoplastic and thermosetting. Thermo-plastics soften and flow when heated and are normally shaped by heat and pressure. They will soften and flow again when re-heated. Vinyl, used in the manufacturing of LP's, is a thermoplastic.

Thermo-setting polymers are moulded under heat and pressure. A chemical reaction occurs so that once molded they do not soften when re-heated and will normally char before melting. Most 78s are made of thermosetting polymers.

4.2 Mass Produced Coarse Groove Discs

4.2.1 General

Several types of mass produced discs have been manufactured during the past 100 years. The commonest are the shellac or 78. The other types are comparatively rare. If, however, you have some of these other varieties in your collection, or you are not sure what type of disc they are, seek specialist advice.

4.2.2 Shellac Discs

The first shellac discs date from the early 1900s. Although they are known as "78s", many of the early ones were designed to be played at other speeds. Speeds of between 60 and 100 rpm are known.

Shellac is a composite word; it's a combination of shell and Lac. The word "Lac" is the Hindu name of an insect that infests certain types of trees. The Lac draws sap from these trees, processes it through its digestive system and secretes the sap as a resin to form an attached protective shell around its body. The shell is generally smaller than a grain of rice and harvest involves scraping off the encrusted shells from twigs and branches.

After World War II, resins such as Vinsol, Valite, vinyl chloride acetate and other commercial resins replaced organic shellac as the main binder. These polymers are slightly more stable than organic type discs and it is often difficult to distinguish between shellac and shellac type discs by visual inspection.

Determining the causes of shellac disc degradation is difficult because a very wide range of qualities of shellac and "fillers" have been used by manufacturers. One cannot, therefore, expect consistent behaviour from stored shellac discs. The disc properties are as much a function of the filler as they are of the cementing agent. The fillers used run the gamut of natural cellulosic materials as well as of minerals. Record manufacturers would introduce scrap as filler into new mixtures. It was not uncommon for the scrap to include soft drink bottles, litter, pieces of masonry or other unwanted material, all of which were ground up and mixed in with the next batch of compound. The manufacturers would also recycle returned, unsold shellac discs.

In general, shellac discs are relatively stable. The curing process of shellac during disc manufacturing generates a chemical reaction where certain simple molecules such as water and ammonia are eliminated. Curing causes shellac to shrink, increasing its density and its brittleness. This shrinkage continues at a much slower rate after the disc is manufactured. The speed at which shrinkage occurs is a function of storage temperature, storage humidity and completeness of cure. Storage stabilities of the fillers vary widely. Organic materials in the aggregates are susceptible to fungus attack, while shellac itself is resistant to fungus attack.

In a proper storage environment, these discs suffer a slow, progressive embrittlement of the shellac. This embrittlement causes a fine powder to be shed from the disc after each play-back. The behaviour of the other aggregate components is unpredictable, due to the wide combinations and variety of materials (and of material quality) that were used.

4.2.3 Vulcanite (hard rubber) Discs (early Berliner records)

Vulcanite was the first material used commercially by Berliner and provided the necessary basis for the exploitation of the flat disc. Vulcanite is a rubber based composition and is stable in the dark. It retains its appearance and properties very well. In response to light and/or heat the material loses sulphur then becomes brittle and loses its shine. The degradation can be demonstrated when playing an afflicted Berliner. The surface of the disc is shaved off by the pressure of the stylus against the groove wall.

4.2.4 Columbia Discs (laminated discs)

In 1906 Columbia introduced the Marconi Velvet Tone developed by Giulemino Marconi. The manufacturing technique involved using a craft paper core cut to approximate record size. After the core was carefully flattened and dried, it was covered with a powdered shellac compound of a thin uniform thickness. The dust-coated core was put in an oven and the dust fused to the core. For two-sided records, the operation was repeated for the other side. The advantage of this construction was that the amount of surface material needed to carry the music grooves could be kept very small. This economy allowed the use of the best polymer available at that time. Edison was to use this idea in 1912/13, in the manufacturing of his Diamond Disc.

In 1922 Columbia returned to the laminated record, this time with a coarser compound for the powder core that was bonded between two discs of craft paper.

4.2.5 Edison Diamond Discs

The Edison Diamond Disc has the distinction of having been made of the first completely synthetic polymer, a material called phenol (phenol was also used in the manufacture of Bakelite). The Edison Diamond Disc is a laminated disc made up of a thick core and thin varnish layers covering each of its sides.

Prolonged contact with moisture or severe changes in humidity may cause damage to the surface through moisture absorption. In general, phenol is very stable and presents no serious degradation problems, neither is it prone to attack by bacteria, fungi or insects although, occasionally, under humid conditions moulds may grow and cause some surface attack on a nutrient filler such as wood or cotton, or be supported by a nutrient contaminator on the surface.

4.3 Instantaneous Discs (Acetate Discs)

Prior to the advent of magnetic tape, instantaneous recordings were made on disc. The chemical make up of these discs had to be a compromise between ease of engraving and the quality of the recording that resulted. Since the 1930s, most blank instantaneous discs have been manufactured with a base, usually aluminium (although glass and steel were used during the war years and cardboard for inexpensive home recordings), that was coated with nitrocellulose lacquer plasticized with castor oil. Because of the lacquer's inherent properties, these acetate discs are the least stable type of sound recording and expert advice must be sought before attempting to play these discs.

The gradual loss of plasticizer causes progressive embrittlement and the irreversible loss of sound information. Because the coating is bonded to a core which cannot shrink, internal stresses result, which in turn cause cracking and peeling of the coating. In addition, nitrocellulose acetate decomposes continuously and over time reacts with water vapour or oxygen to produce acids that act as a catalyst for several other chemical reactions. As with most chemical reactions, these reactions are accelerated with elevated temperature and humidity levels.

Other materials were used to make instantaneous discs. Examples may be found with a gelatine coating or made of uncoated zinc. As with acetate discs, these are usually unique recordings and fragile. Seek expert advice before attempting to play them.

4.4 Vinyl Discs (LPs)

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, state 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%) of fillers, stabilisers, pigments, 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 on-going dehydrochlorination, which is the release of hydrogen chloride (HCI, which, when combined with water, makes hydrochloric acid) 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 HCI. Sufficient effective stabilizer remains in a plastic phonograph disc to protect it for several decades after pressing.

4.5 Cylinder Recordings

Early cylinders, both the blanks used for home recordings, and the prerecorded, were made by coating a solid core, often made of plaster, with one of several types of natural polymer. One form of coating material was a type of wax hence the commonly used description "wax cylinder".

Later types, such as the "Blue Amberol" series of recordings, were moulded from polymers without using a plaster core.

All cylinders are now very fragile. The polymers, both coating and monolithic, and the core materials are decaying and irreversibly breaking down. Urgently seek advice if you have any cylinders in your collection.

5. 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 discs:

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

5.1 Foreign Matter Deposits

5.1.1 The Dangers of Dirt

Dirt can be classified into two categories:

* Foreign matter deposits which are not part of the original object, such as grease from fingerprints, soot, stains, adhesives, etc.
* 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 disc preservation in a number of ways. 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 embedded permanently into thermoplastic substances. Only a small point of the stylus is actually making contact with the groove walls. A force of 15 mN (milliNewtons) or 1.5 grams from the stylus on such a minute surface translates to several tonnes of pressure per square centimetre. The resulting drag generates enough heat for the polymer to partially melt (though not enough to deform), causing a microscopic flow around the stylus into which dust can be embedded permanently.

5.1.2 To Minimize Foreign Matter Deposits

* Never touch the grooved surface of a disc. Handle by the edges.
* Remove a disc from its outer sleeve by bowing the sleeve open by holding it against the body and applying slight pressure with one hand. Pull out the inner sleeve and the disc by holding a corner of the inner sleeve with the other hand. Avoid pressure on the disc itself: this would press any dust trapped inside the inner sleeve into the record surface.
* Remove the disc from the inner sleeve by bowing the sleeve and letting the disc slip gradually into an open hand so that the edge falls on to the inside of the thumb knuckle joint. The middle finger should be extended to reach for the centre label of the disc. Never reach into the sleeve.
* To hold a disc, place a thumb on the edge of the disc and the fingers of the same hand on the centre label for balance. Use both hands on the edge to place the disc on to a turntable.
* Discs should not, unnecessarily, be left exposed to open air. Return items to their sleeves when not in use.
* Do not use paper or cardboard inner sleeves and do not store records without inner sleeves.
* Use soft polyethylene inner sleeves. Do not use sleeves made of PVC.
* Do not place discs 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 discs are handled.
* Keep storage facilities as clean and dust-free as possible. The air conditioning system should be equipped with dust filtering equipment.
* Do not use carpets in the storage or work areas. They create and hold dust which is blown into the air by vacuum cleaning. Carpets can also build up static electricity charges. Use a washable flooring material which does not build up static electricity.

5.1.3 Cleaning

Please Note - Refer to manufacturer safety data sheets for information on the use of any chemicals mentioned herein.

Since dust is usually held in place by electrostatic attraction, dry wiping does not work effectively. The friction of the wiping action will increase the electrostatic charge and attract dust back to the surface - often in increased quantity.

Distilled water is commonly used because:

* Its precise chemical composition is known.
* It will not leave deposits behind
* It is safe and non-toxic.
* It is inexpensive.
* It disperses static charges and counteracts the increase in conductivity from the pick-up of salt deposits from finger prints.

Water alone cannot, however, dissolve grease. A surfacant additive is necessary, therefore, to break the grease surface bonds and to allow the water to penetrate and disperse the grease. Discs are best cleaned by using a machine such as the Keith Monks, VPI or Nitty Gritty using a surfacant in distilled water. These machines evenly disperse the liquid over the surface of the disc and then vacuum clean the surface leaving it clean and dry. Records should be cleaned before each playback.

An airgun or aerosol of compressed air should be kept handy to blow light dust off surfaces.

Berliner Vulcanite discs showing signs of acid build up (loss of surface shine and slight groove damage causing dust when played) should be cleaned with a standard cleaning solution.

Acetate discs showing signs of palmitic acid deposits (a white, greasy substance on the disc surface) should be cleaned the same way as vinyl discs. Add two parts of ammonia to 100 parts of the standard cleaning solution. UNDER NO CIRCUMSTANCES SHOULD THIS AMMONIA SOLUTION BE USED ON SHELLAC BASED DISCS.

5.2 Surface Deformations

Since the surface of a disc is the information carrier, it is critical that the surface is well cared for. Physical deformations such as warping of discs or shock caused by dropping them, will directly affect the integrity of the sound information.

5.2.1 To Minimise Deformations

* Never leave discs near sources of heat or light (especially ultraviolet light) as polymers are adversely affected by both.
* Do not place heavy objects on top of discs. Discs should never be placed on top of each other.
* Shelve discs vertically; do not stack at an angle or horizontally.
* Do not use shelving units with supports that put more pressure on one area of a disc or with supports more than six inches apart.
* Do not use PVC coated shelves. The plasticisers in the PVC may soften the polymers of the discs.
* Do not file discs of different sizes in the same shelf area. Smaller items may get lost or damaged and larger items subjected to uneven pressures.
* Completely remove any shrinkwrap on LPs. The shrinkwrap continues to shrink and can lead to warping of the disc.

5.3 Environment

A proper environment for the storage of sound recordings is essential to retard the degradation mechanisms. The temperature and humidity must be controlled to provide the correct storage environment. Elevated temperature and humidity can affect the chemical properties of the polymers and can also encourage the growth of fungus. Wide or rapid fluctuations in the storage environment will also accelerate degradation mechanisms.

5.3.1 Shellac Discs

High humidity levels accelerate the embrittlement of shellac discs. This embrittlement causes a fine powder to be shed from the disc after each playback, effectively scraping away groove information. The severity of the embrittlement is unpredictable because of the wide variety, combinations and quality of materials used during production of the discs. The average shellac content in a shellac disc is about 20% with the remaining 80% composed of aggregates or fillers. Organic materials in the aggregates are susceptible to fungus attack but the shellac itself is said to be fungus resistant.

5.3.2 Acetate Discs

Shrinkage of the lacquer coating due to loss of plasticiser is the primary destructive force of these discs. This leads to cracking of the coating without any warning and, in extreme case, delamination of the disc. These discs must be copied as swiftly as possible by an expert. Excess moisture will accelerate the plasticiser loss. Acetate discs decompose continuously and, over a period of time, react with water vapour or oxygen to produce acids that in turn act as catalysts for several other chemical reactions. One of these is the release of palmitic acid, a white waxy substance that is deposited on the surface of the discs. Acetate discs are very susceptible to fungus growth. Excess heat will probably accelerate the loss of adhesion of the coating.

5.3.3 Vinyl Discs

Vinyl discs are adversely affected by ultraviolet light and thermalcycling (heat fluctuations). The consequence of thermal cycling is that each cycle of temperature change results in a small, irreversible deformation. These deformations are cumulative. Vinyl discs are resistant to fungal growth and are unaffected by high humidity levels.

5.3.4 Correct Storage Environment

* Store discs at a stable, maintained temperature of between 15EC and 20EC. The fluctuation of temperature should not slowly vary more 2EC in a 24 hour period.
* The relative humidity should be maintained at between 30% and 40% with a slow fluctuation of no more than 5% in a 24 hour period.
* Maintain proper ventilation and air circulation of the storage stacks at all times to avoid localised variations from the optimum storage conditions (Microclimates).
* Keep discs in darkness when not being accessed. Fit light fixtures that do not produce ultraviolet radiation in excess of 75mW/1m (microwatts per lumen).

6. Conclusion

Over the past century, recorded sound has become an intrinsic part of our culture. Upon hearing an early sound recording in 1888, Sir Arthur Sullivan declared "I was astonished and somewhat terrified at the result of this evening's experiments - astonished at the wonderful power that 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 lifespans shortened considerably by both internal and external forces. By undertaking certain precautionary measures, custodians of the heritage of sound can considerably lengthen their collection's lifespan and, thus, preserve a rich and invaluable world of sound.


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