Lacquer disc preservation at the Hoover Archives

After selecting an item for preservation, the archives staff visually assesses the disc’s condition.
After selecting an item for preservation, the archives staff visually assesses the disc’s condition. The disc in this image suffers from a variety of problems, including a compromised and acidic sleeve.
This disc also suffers from the presence of palmitic acid
More important, this disc also suffers from the presence of palmitic acid, a white, crystalline, oily substance caused, it is thought, by the leeching of a castor additive from the disc’s nitrocellulose layer. The palmitic acid spans the disc, covering both the playing surface and the nongrooved area.
A close-up of palmitic acid on a lacquer disc.
A close-up of palmitic acid on a lacquer disc.
The same disc viewed through a microscope. Note that palmitic acid is present both in the groove and in the area in between grooves.
The same disc viewed through a microscope. Note that palmitic acid is present both in the groove and in the area in between grooves. Because disc playback is extremely sensitive to any kind of debris in a groove, palmitic acid damage results in an excessive amount of noise. Consequently, the disc must be cleaned before a digital preservation copy can be created.
A member of the archives staff applies a cleaning solution to neutralize palmitic acid and remove debris from the disc’s playing surface.
Here a member of the archives staff applies a cleaning solution to neutralize palmitic acid and remove debris from the disc’s playing surface. Then, after using the vacuum arm on the right, the disc is rinsed with deionized water and again vacuumed dry to ensure as clean a groove as possible. (Note: The markings etched in grease pencil, visible in greater detail in the previous two slides, contain vital information about the content and context of the recording. Because these markings did not interfere with the grooved surface–that is, the area containing the sound information on the disc–it was decided not to clean that area, thus preserving the provenance of both the content and its carrier.)
Again seen through a microscope, the same disc is now free of noise-creating debris and  ready for digitization.
Again seen through a microscope, the same disc is now free of noise-creating debris and ready for digitization.
A member of the archives staff makes a high-resolution digital copy of the disc
After having calibrated the turntable for optimum playback and selected appropriate styli, a member of the archives staff makes a high-resolution digital copy of the disc. (Note: The CD-Rs in the photos are used to create lower-resolution access copies. For preservation, Hoover creates 24-bit, 48- ksps WAV files in accordance with the recommendations of the Audio Engineering Society, the International Association of Sound and Audiovisual Archives, and the Association for Recorded Sound Collections.)
Now cleaned and digitized, the disc is placed in a sturdy, new, acid-free sleeve for long-term storage.
Now cleaned and digitized, the disc is placed in a sturdy, new, acid-free sleeve for long-term storage.