Lacquer discs form the heart of the Ngā Taonga audio collection – we have thousands of them. They were the default technique for recording sound over a long period from the 1920s until well into the 1950s when magnetic tape took over.
Most of the lacquer discs in the collection consist of steel or aluminium platters covered in a layer of nitrocellulose, an early kind of plastic. Sound from a microphone was converted to a vibration in a cutting tool which etched a groove into the lacquer coating as the disc rotated. Playback was effected by a stylus connected to an amplifier which converted the vibrations from the groove back into sound. Musical 78rpm discs and later polyvinyl LPs work on the same principle, but to enable mass duplication these were pressed from a metal mould made from an original cut lacquer.
Among the thousands of lacquer discs in the collection is a talk by Dame Ngaio Marsh, recorded in 1954. The full recording can be heard here. This 12-inch disc was digitised in 2005 by one of our sound archivists who discovered quite severe damage to the lacquer. This was likely caused by the lacquer and metal core expanding at different rates as temperatures changed, which led to cracks in the lacquer. The result here is that the lacquer layer has peeled away, rendering the end of the interview unplayable. The archivist at the time noted: “an attempt was made to replay this section, but it retracks badly.” It seemed as though we might never know what Ngaio Marsh was talking about beyond the endless repetition of “the dubious flowering of some degraded cellar.”
You can hear the ‘retracking’ repetition in this 2005 digitisation:
A recent request to hear this audio prompted Sound Archivist Sandy Ditchburn to have another go at digitising the disc. “After discovering the poor quality recording I made an attempt to re-digitise the disc using new computer technology and preservation techniques,” she explains. “First, I chose a stylus that could capture the higher frequencies that were missing in the initial digitisation attempt. Then, monitoring it closely due to the bad condition of the disc, I began recording.”
By manually controlling the movement of the stylus, Ditchburn was able to capture all of the audio on the disc. Then, in the audio equivalent of gluing together a shattered ceramic pot, she reconstructed the recording. “I pieced the skipping audio together with professional audio editing software. The resulting audio still contains ‘pops’ where the stylus hits the cracks in the lacquer but the content has been completely recovered in the correct sequence, as it was spoken by Ngaio Marsh in 1954.”
You can hear the correctly sequenced, non-repeating 2019 digitisation:
All photos by Sandy Ditchburn.