Chemical Composition of Records (credits)
The information below is an excerpt from the article "The Care and Handling of Recorded Sound Materials" by Gilles St-Laurent at the Music Division National Library Of Canada, January 1996. The complete text can be found at the Conservation OnLine site at http://palimpsest.standford.edu.
|Table of Contents
rubber) was the first material used commercially by Berliner and provided the necessary
basis for the exploitation of the flat disc.
In 1839 Hancock in England and Goodyear in the US independently discovered vulcanization. Vulcanization is the process of treating crude rubber with sulfur or sulfur compounds in varying proportions and at different temperatures. The result is an increase in the rubber's strength and elasticity, yielding either soft rubber or vulcanite. Vulcanite has been used to make combs, buttons, jewels, fountain pens, musical instruments, etc.
Vulcanite is stable in the dark and retains its appearance and properties very well. In response to light and/or heat the material loses sulfur then becomes brittle and loses its shine. Light induces oxidation of the rubber and forms oxides of sulfur and sulfuric acid in the presence of humidity. The acidity builds up to a level at which the degrading plastic is attacked and eventually decomposes1. 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.
Vulcanite also posed problems in the production of discs. The uneven shrinkage during cooling caused severe warping; entrapped gas would produce blisters; hard particles create loud pops and clicks; and the coarseness of the Vulcanite structure produced terrible background noise.
|Shellac Discs||The first shellac
discs date from the early 1900s. Shellac is a composite word--it's a combination of shell
and lac. The word is a Hindus 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 it
so that it becomes an attached protective shell around its body. Thus the shell is
generally smaller than a grain of rice. Harvest involved scraping off the encrusted shells
from twigs and branches.
After WWII resins such as Vinsol, Valite, Vynil chloride acetate and other commercial resins replaced organic shellac as the main binder. These plastics are slightly more stable than organic type discs. It is often difficult to distinguish between shellac and shellac type discs by inspection.
Determining the causes of shellac disc degradation is rather difficult because a very wide range of qualities of shellac and "fillers" have been used by manufacturers. Therefore one cannot expect consistent behavior of all 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.
For example, two separate chemical analyses of "typical" shellac discs showed the following:
The average shellac content in these "shellac" discs is approximately 15% shellac.
Also, record manufacturers would introduce scrap as filler into new mixtures. The manufacturers would recycle returned, unsold shellac discs. It was not uncommon for the scrap to included soft drink bottles litter, pieces of masonry or other unwanted material, all of which were ground up together and mixed in with the next batch of compound.4
|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.5
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 the best plastic 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.
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 or ammonia molecules are eliminated. Curing causes shellac to shrink, increasing its density and its brittleness. This condensation continues at a much slower rate after disc manufacturing. The speed at which condensation occurred is a function of storage temperature, storage humidity and completeness of cure. (The condensation reaction reduces the potential concentration of reacting elements. A semi-quantitative measure of the cure of shellac is its solubility in alcohol. Raw shellac is totally soluble in alcohol and completely cured shellac is insoluble, and the extent to which condensation has proceeded determines the degree of solubility of a shellac.6) Thus the condensation becomes the primary degenerative force. The internal reaction of the material and the rate at which the reaction occurs are related to storage temperature, storage humidity (moisture increases the condensation reaction rate) and completeness of the cured shellac.
Storage stability of these 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 playback. 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.
|Edison Diamond Disc||The Edison Diamond
disc has the distinction of having been made of the first completely synthetic plastic, 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 a thin varnish layers covering each of its sides.
The ¼" core, which is also know as a powder blank, was manufactured by compressing the following ingredients in the following proportions:7
The varnish would be applied to the blank by a brush as the blank rotated slowly. Four applications or coats were given each blank face with a drying period between. After the last coat the varnished blank would be placed in a steam-heated oven. This completed the drying and also effected a partial reaction of the varnish ingredients
Prior to pressing, the blanks would be heated before applying pressure to soften. After the pressure was applied the heat was left on to complete the curing or reaction of the varnish. Then the moulds were cooled and the pressure released.
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 contaminant on the surface.
1.Morgan, John.--Conservation of Plastics: An introduction to their history, manufacture, deterioration, identification and care. London, England: Plastics Historical Society; The Conservation Unit, Museums & Galleries Commission, 1991. Page 18.
2.Isom, Warren Rex.--Centennial Issue... The Phonograph and Sound Recording After One-Hundred Years. -- Audio Engineering Society. Volume 25, Number 10/11, October/November, 1977. Page 719.
3.Pickett, A.G.; Lemcoe, M.M.--Preservation and Storage of Sound Recordings.--Washington, D.C.: Library of Congress, 1959. p. 24.
4.Isom, Warren Rex.--Record Materials, Part II: Evolution of the Disc Talking Machine--Centennial Issue... The Phonograph and Sound Recording After One-Hundred Years.--Audio Engineering Society. Volume 25, Number 10/11, October/November, 1977. Page 720.
5.IBID. Page 721.
6.Pickett, A.G.; Lemcoe, M.M.--Preservation and Storage of Sound Recordings.--Washington, D.C.: Library of Congress, 1959. p. 25.
7.Burt, Leah S.-- Record Materials, Part I: Chemical Technology in the Edison Recording Industry--Centennial Issue... The Phonograph and Sound Recording After One-Hundred Years.--Audio Engineering Society. Volume 25, Number 10/11, October/November, 1977. Page 717.
8.The stability of the newest format, the compact disc, has not yet been determined.
9.Pickett, A.G.; Lemcoe, M.M.--Preservation and Storage of Sound Recordings.--Washington, D.C.: Library of Congress, 1959. p. 31.
10.Edge, Michelle.--The Deterioration of Polymers in Audio-Visual Materials.--Archiving the Audio-Visual Heritage; Third Joint Technical Symposium; Technical Coordinating Commitee and Unesco.--1992. Page 33.
11.International Institute for Conservation--Canadian Group and the Canadian Association of Professional Conservators.--Code of Ethics and Guidance for Practice: for Those Involved in the Conservation of Cultural Property in Canada.--The International Institute for Conservation of Historic and Artistic Works-Canadian Group/The Canadian Association of Professional Conservators (CAPC).--Ottawa: 1989, second edition. Page 19.
12.Moncrieff, Anne; Weaver, Graham.--Science for Conservators: Cleaning.--London: Crafts Council, 1983. Page 14.
13.IBID. Page 14.
14.Please Note: Refer to manufacturer safety data sheets for the use of any chemicals mentioned herein.
15.Morgan, John.--Conservation of Plastics: An introduction to their history, manufacture, deterioration, identification and care. London, England: Plastics Historical Society; The Conservation Unit, Museums & Galleries Commission, 1991. Page 18.
16.16 Pickett, A.G.; Lemcoe, M.M.--Preservation and Storage of Sound Recordings.--Washington, D.C.: Library of Congress, 1959. Page 41.
17.N.B. ANSI/AES are preparing a report entitled Environment Storage Conditions which will deal with the proper storage environment for tapes. It is to be completed by the fall of 1991.
18.Moogk, Edward B.--Roll Back the Years: History of Canadian Recorded Sound and its Legacy, Genesis to 1930.--Ottawa: National Library of Canada, 1975. Page viii
The Care and Handling of Recorded Sound Materials