5.2.3 Cleaning and Carrier Restoration
5.2.3.1 Grooved media may be adversely affected by past use, or through natural decomposition of the constituent materials, hastened to a greater or lesser degree by environmental storage conditions. Debris including dust and other airborne material can accumulate within the grooves, and fungal growth may be present where climatic conditions have allowed. This is particularly common with instantaneous cylinders. In addition, lacquer discs may experience exudation of the plasticisers from the lacquer itself. This typically has a white or gray mould-like appearance, but is distinguished by a greasy consistency. Mould, on the other hand, is typified by feathery or thread-like white or gray growth. Each of these conditions will compromise the ability of the replay stylus to follow the groove pattern accurately, and so appropriate cleaning of the carrier is necessary.
5.2.3.2 The most appropriate cleaning method will depend on the specific medium and its condition. In many cases a wet solution will produce the best results, but the choice of solution must be made carefully, and in certain cases it may be best to avoid the use of any liquids. Record cleaning solutions which do not disclose their chemical composition should not be used. All decisions about the use of solvents and other cleaning solutions should only be made by the archivist in consultation with the appropriate technical advice by qualified plastics conservators or chemists. It can however be stated that lacquer and shellac discs, and all types of cylinder, should never be exposed to alcohol, which may have an immediate corrosive effect. Shellac discs frequently contain absorbent fillers which can expand on sustained contact with moisture, and so should be dried immediately after cleaning with any wet solution. Any wet cleaning process should avoid contact with paper disc labels.
5.2.3.3 Castor oil has commonly been used as a plasticiser in the production of cellulose nitrate lacquer discs, which, as it exudes from the disc surface typically breaks down into palmitic and stearic acids. The loss of plasticiser causes the coating to shrink and consequently crack and peel away from the base. This is known as delamination. Several solutions have been employed successfully in removing the exuded acids (see in particular Paton et al 1977; Casey and Gordon 2007, p27).It has been observed however that after cleaning, lacquer discs may continue to degrade at an accelerated rate. It is sensible therefore to create digital copies of the material held on cleaned lacquer discs as soon as possible after cleaning. It must again be stressed that the effect of all solvents should be tested before use. Some early lacquer discs have a gelatine rather than cellulose nitrate playing surface for example, which is soluble and would instantly suffer irreversible damage if treated with any liquid solution.
5.2.3.4 Certain other media may not be appropriate for wet cleaning, including shellac and lacquer discs which were manufactured with paper or card layers beneath the playing surface. Similarly, lacquer discs displaying cracking or peeling surfaces must be treated with great care, and instantaneous cylinders should be cleaned with a soft dry brush only, applied along the groove path. However, where mould spores are thought to be present, the utmost care should be taken to minimise cross contamination. Special care should be taken when cleaning moulds and spores as these may cause serious health problems. Operators are strongly advised to obtain professional advice before commencing work on such infected materials.
5.2.3.5 In cases where wet cleaning is deemed appropriate, it should be carried out with both the solution and carrier at room temperature, to avoid any damage to the carrier caused by thermal shock.
5.2.3.6 Often the most effective and efficient method of wet cleaning is to use a record cleaning machine employing a vacuum to remove the waste liquid from within the groove, such as those made by Keith Monks, Loricraft or Nitty Gritty.
5.2.3.7 Particularly dirty carriers, or those with stubborn marks such as dried-on paper deposits, may be more appropriately cleaned using an ultrasonic bath, into which the carrier (or portion of the carrier) is placed. The process works by vibrating a solution around the item, loosening dirt deposits.
5.2.3.8 In cases where it is not possible or appropriate to employ such equipment, hand washing may be carried out using an appropriate short bristled brush. Clean tap water may be used in the washing process, but should always be followed by a thorough rinse in demineralised water to remove any consequent contamination.
5.2.3.9 In addition to cleaning, some further form of restoration may be required. Shellac discs and cylinders of all types are brittle and liable to break if mishandled, and shellac will melt and warp at high temperatures. The exudation of plasticiser from lacquer discs causes the lacquer layer to contract upon a stable metal or glass base, creating stresses between the layers and resulting in cracking and peeling of the lacquer playing surface. Reconstruction of broken discs and cylinders is ideally done without resorting to glues or adhesives, as these inevitably form a barrier between the parts being joined which, however small, will be audible. Such processes are also generally irreversible, allowing for no second chances. The manufacturing processes used in replicating both shellac discs and cylinders will often result in a degree of internal stress in the carrier. If broken, the divergent stresses in the constituent pieces may cause them to contort somewhat. To minimise the effect of this, broken carriers should be reconstructed and transferred as soon as possible after the breakage occurs. The individual parts of broken carriers should be stored without touching. Storing them unsecured in their reconstructed form may encourage the finely detailed broken edges to rub together, causing further damage.
5.2.3.10 Shellac discs are usually best reconstructed on a turntable, upon a flat platter larger than the disc itself (another, disposable or non-archival disc is often ideal). The pieces are placed upon it in their correct positions and held in place around the centre spindle with re-usable pressure sensitive adhesive putty such as Blu-Tack, U-Tack, or similar around the outside of the disc.Where discs are thinner around the edge than in the middle, the putty may be used to raise the edges to the correct height. Take note of the direction through the groove that the stylus will travel: where the pieces cannot be perfectly vertically aligned, it is better for both the stylus and the resulting transfer that the stylus be obliged to drop down onto a lower fragment rather than be pushed up abruptly onto a higher one.
5.2.3.11 Cylinders which have suffered a neat break can often be reconstructed around the playback mandrel using 1/4 inch splicing tape as a form of bandage. More complex breakages will require specialist help.
5.2.3.12 Flakes from peeling lacquer disc surfaces may be temporarily fixed to allow the disc to be played, using tiny amounts of petroleum jelly between the flake and disc base. The long term effects of this procedure are likely to be deleterious, and it is used to attempt replay of discs which are judged to be unplayable by any other currently practicable means.
5.2.3.13 Where it is possible to play a warped or bent disc without flattening it, this should be the preferred option, as the risks associated with disc flattening described below will attest. The ability to play a warped disc can often improve when the rotational speed of the disc is reduced (see 5.2.5.4).
5.2.3.14 Shellac discs may be flattened in a laboratory (i.e., non-domestic) fan-assisted oven. The disc should be placed on a sheet of pre-heated toughened glass, and it is imperative that both disc and glass be clean, to prevent dirt fusing with the disc surface. There is a danger that in curing vertical warpage, some lateral warpage may occur. The disc should therefore not be heated any more than it has to be, and a temperature of around 42C is often sufficient (Copeland 2008 Appendix 1).
5.2.3.15 Flattening discs is a useful process because it can make unplayable discs playable. However, current research into the procedure of flattening discs with heat shows that it causes a measurable rise in subsonic frequencies, even in the low audible frequency range (Enke 2007). Though the research is not conclusive the point should be noted in determining whether to flatten a particular disc. The analysis of the affect of flattening was carried out on vinyl discs and whether it applies to shellac is yet to be determined, though the lower temperatures associated with treating shellac make it much less of a risk. Nonetheless, the possibility of such damage has to be weighed against enabling the playing of the disc.
5.2.3.16 Though it is strongly advised not to attempt to permanently flatten an instantaneous disc (and any attempt is likely to be unsuccessful and damage the disc surface), in some instances the warpage may be temporarily reduced by clamping or otherwise fixing the disc edges to the turntable. Great care must be taken, especially with lacquer discs whose surface may be damaged if placed under stress. Laminated flexible discs with a warp may have been rendered flat by placing the disc on the vacuum platter of a disc cutting lathe and carefully bringing the disc flat. All physical treatment should be undertaken with great care to avoid damage.
5.2.3.17 Some replicated discs have been produced with a non-centric spindle hole. It is preferable to play such discs on a turntable with a removable spindle or to raise the height of the disc above the spindle using, for example, waste discs and rubber interleave. In the latter case the height of the pickup arm should be raised at the supporting column by the same amount. It is possible to re-centre the hole using a reamer or drill, but such invasive approaches should be undertaken cautiously and never with unique or single copies. Altering the original artefact may well result in loss of secondary information.
