Vinyl Record

Instantaneous Discs

Instantaneous or acetate discs first came into common use in the 1930’s and were used for commercial, broadcast and home recording prior to the perfection of magnetic tape recording technology.  In fact they were in common usage well into the 1960’s

Acetates consist of a soft plastic coating over a base disc, generally aluminium, although many other materials have been used such as glass, zinc and cardboard.  The aluminium, or other, base was coated with nitrocellulose lacquer plasticised with castor oil.  The grooves are cut into the surface of the blank disc by a machine (often called a cutter or lathe) which produces the grooved surface which can be played just as commercially produced discs.  Such discs can generally be recognised by looking at the base material through the centre hole.  Acetate discs also usually have a second hole near the centre to locate on a separate pin on the cutting machine which reduces `slippage’ during the cutting process.

The audio quality of such discs is generally good but they are inherently unstable and with time they will deteriorate and become unplayable.  Generally it is the surface coating of nitro-cellulose acetate which deteriorates rendering the recording unplayable.  In other cases the aluminium can become bent, the glass break or the cardboard becomes damaged (eg. by exposure to water).

Deterioration of the coating is marked by the appearance on the disc surface of a white powder (which can often be mistaken for mould).  This deposit is caused by the migration of the castor oil plasticiser to the surface of the disc.  Eventually the acetate coating can begin to come detached from the disc core, exfoliating in flakes and leaving the disc core exposed.

The surface of acetate discs may be cleaned from debris by washing in water, possibly containing a small amount of mild detergent, and then rinsing in demineralised water.  If using a detergent first try it on part of the `uncut’ disc to ensure that it will not damage the playing surface.  Be careful not to use any abrasive material on the surface and to keep the centre label dry, especially if it contains important information.  The disc should be left to dry in clean air at normal room temperature.  Avoid all chemical cleaners.  Various machines can be purchased which have turntables and carefully directed sprays and brushes along with vacuum suction to remove the water and leave the disc dry ready for playback.  Ultrasonic baths can also be used in which discs are suspended in a container of demineralised water and ultrasonic waves are passed through the water dislodging any ingrained dirt.  Exfoliated acetates are at present unrecoverable.

The surface of acetate discs have to be soft enough to cut and therefore they will not stand repeated playback.  Copy them to another format, preferably in one replay, using the correct diameter stylus.

Acetates are generally to be found in tin boxes or in board sleeves lined with thick cellophane which has usually shrunk and thus distorted the sleeve.  Acetate discs should be placed in acid free sleeves (but no sleeve can prevent the deterioration of the disc) and stored vertically on shelves with dividers every few discs.

RISKS  The surface material, nitro-cellulose acetate, remains soft and unstable and can contract and crack eventually exfoliating from its metal core.  The discs are particularly prone to mould growth.  The crystallisation of castor oil (often used as a plasticiser) can resemble mould and microscopic analysis is necessary to determine the exact nature of the deposit.  Shrinkage of the lacquer coating due to the loss of the castor oil platiciser causes embrittlement of the playing surface.  Because the aluminium core cannot shrink with the lacquer stresses result which causes the cracking & exfoliation of the playing surface.

CONSERVATION PRACTICE  Cleaning is extremely difficult because of the soft composition of the surface layers.  It is possible to seal down some exfoliating surfaces in order to play them but this is a laboratory technique.  Do not attempt to play these discs as one playing with an incorrect weight or stylus can irreparably damage the disc.  Arrange to have the audio content copied to a more stable medium as soon as possible.

HANDLING  Fingers should be kept off the playing surface, the disc being supported with the fingers supporting the centre label area and the thumb on the outside rim.  Cotton or latex gloves are recommended.

STORAGE  Store discs horizontally with layers of acid-free tissue between each disc.  Avoid excessive weight in the pile.

Instantaneous disc showing exfoliation

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