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Fundamentals of AV Preservation - Chapter 1

2.1 History | 2.2 Materials and Preservation Risks | 2.3 Reproduction Methods | 2.4 Best Practices for Storage and Handling

Shellac discs have no significant degradation mechanisms under normal conditions and are a robust format in all regards except one. Their rigidity and composition make them prone to breakage through mishandling. Excessive pressure or dropping a shellac disc will almost certainly result in breakage.

There are three main types of instantaneous discs that are found in collections. These are aluminum-based lacquer discs, glass-based lacquer discs, and aluminum discs. Glass-based lacquer discs replaced aluminum during World War II when the demand for metal became great. 

laquer disc1   laquer disc2


Lacquer discs have multiple degradation mechanisms. Over time, the lacquer layer can undergo chemical and dimensional shifts that cause it to separate from the base glass or aluminum layer, leading to what is referred to as delamination.

delaminated disc   delaminated disc 2


Once delamination has occurred there is no way repair the damage; however, there are warning signs that can alert you in time to successfully transfer the signal on those discs about to suffer delamination. Early signs consist of a whitish film covering the disc, consisting primarily of palmitic acid. Palmitic acid is a chemical used in the creation of lacquer discs; this leaching out of the palmitic acid is a major contributor to delamination. At this stage, where the palmitic acid is leaching out, but the lacquer has not yet begun to crack, it may still be possible to have the disc cleaned by a professional and the signal transferred from the disc.  

Lacquer discs are also fragile and rigid, making them prone to breakage. This is particularly true for glass-based lacquers.

Aluminum discs do not tend to have degradation mechanisms, but they do have one issue that can manifest through mishandling and improper storage. The grooves cut into aluminum discs can be shallow due to the way they were recorded. Combined with the softness of aluminum, significant pressure against the side of an aluminum disc can make the grooves shallower than when originally recorded. This diminishes the integrity of the original recording and sometimes may render it unplayable.

Improper storage, care, and handling practices may result in the following disc issues, impairing reproduction:

  • Matter such as dirt, dust, hair, and other particulates can scratch the surface of the disc, altering the groove or creating separation between the stylus and the groove.

  • Fingerprints, where they exist on the surface of a disc, can speed up or cause degradation.

  • A layer of white film (palmitic acid) covering the disc, indicating the beginning stages of delamination, which must be cleaned off before reproduction.

  • Delamination, resulting in partial or total loss of the signal.

  • Warping causing audio artifacts during impact due to speed variation.

  • Flattened groove walls from too much pressure on the side of the disc, resulting in distorted sound and potentially an inability to track the groove with a stylus.

  • Breakage, resulting in partial or total loss of the signal.

  • Scratches from improper handling and/or transport.

Cylinders

In general, cylinders are fragile and care should be taken not to drop or bump them. Prior to 1902, when more rigid wax formulas were introduced, cylinders were typically made from brown wax. Brown wax cylinders are extremely soft and fragile, are prone to surface scratching and groove wear, and are susceptible to fungal growth. Home recordings made on brown wax are especially high risk; users often shaved off layers of wax in order to reuse the cylinders, making these particular cylinders extremely thin and prone to breakage. Improper storage and handling of these softer wax cylinders may also result in a warping of the grooved surface, resulting in sound artifacts due to speed variations.

Improper storage, care, and handling practices may result in the following cylinder issues, impairing reproduction:

  • Matter such as dirt, dust, hair, and other particulates can scratch the surface of the cylinder, altering the groove, or creating separation between the stylus and the groove.

  • Fingerprints, where they exist on the surface of a cylinder, can speed up or cause degradation.

  • Warping, causing audio artifacts during impact due to speed variation.

  • Breakage, resulting in partial or total loss of the signal.

  • Scratches from improper handling and/or transport.

2.3 Reproduction Methods

Discs

Presently, there are two different ways that the sound recorded on discs is reproduced. The traditional method consists of using a turntable, otherwise known as a record player, which utilizes an electro-mechanical method of reproduction. A stylus of the appropriate size and shape is selected according to the groove dimensions. Any movement that the stylus makes which is not part of the actual recorded signal adds noise and distortion to the audio reproduction. Given the miniscule movements involved in this process, even a small amount of particulate matter or a scratch can significantly impact the resulting sound. It is easy to see how delamination, breakage, or significant scratches may make it impossible to play a disc back.

The other method that is used for reproduction involves scanning, or imaging the groove. Once the image of the groove is captured, the mechanical variation is able to be identified and calculated. These calculated variations are then plugged into an algorithm that generates a digital audio file representing the originally recorded signal. This method is particularly useful when discs are damaged or degraded to the extent that a stylus would not be able to stay in the groove of a disc.

Reproduction via turntable and via imaging are significantly different, but the recorded signal in the original disc results in similar audio results when particulate matter, scratches and other things obscure the groove. Ultimately, careful storage and handling practices are important to the integrity of the content regardless of which reproduction method you choose.

Cylinders

Like discs, there are currently two playback mechanisms for cylinders: the traditional electro-mechanical method and the imaging method. First, a correctly sized mandrel must be chosen for playback; the diameter of the mandrel will correspond to the interior diameter of the cylinder. Then an appropriately sized and shaped stylus must be chosen based on the groove dimensions. As with discs, the movement of the stylus generates electrons and any additional movement caused by scratches or particulate matter will affect the sound.

Cylinders differ from most discs, however, in that their grooves are vertical as opposed to discs’ lateral grooves. The vertically oriented grooves create hill and dales which must be imaged using 3D technology in order to obtain the information necessary to generate a digital audio file representing the originally recorded signal.

2.4 Best Practices for Storage and Handling2

Environment

  • Discs and cylinders should be stored at temperatures between 33 and 54 degrees Fahrenheit, with RH between 30%-50%. Temperatures should not fluctuate more than ±2 degrees within a 24 hour period. RH should not fluctuate more than ±5% within a 24 hour period.

  • Discs and cylinders should be kept away from sources of heat, including sunlight or room lighting.

Housing

  • Discs and cylinders should be stored on their edge or end so that they stand vertically. This will avoid pressure that may cause breakage, warping, groove wall flattening, or otherwise place undue stress on the surface of the disc.

  • Discs should be in sleeves and housing that protect them from external elements and do not generate particulates or react chemically with the disc.

  • Cylinders should be removed from any original cardboard housings. These cardboard housings are known to foster mold growth in humid storage conditions.

  • Cylinders should be stored in appropriate housings that protect them from external elements and do not generate particulate or react chemically with the disc. Cylinders should be housed in specially designed archival boxes containing a foam tube that fits within the cylinder, keeping the cylinder steady without allowing the grooves to touch the interior of the box.

Handling

  • Handle the disc from the edges only. Do not touch the surface of the disc without using non-abrasive, non-shedding gloves.

  • Handle the cylinder from the ends or interior only. Do not touch the surface of the cylinder without using non-abrasive, non-shedding gloves. To pick up a cylinder, insert two fingers into the cylinder and spread your fingers.

Section 3: Magnetic Media ›