Vinyl Record

Disc Bronzing or Disc Rot

Disc bronzing, or disc rot, occurs when the sulphur content contained in CD booklets and printed material corrodes the lacquer coating of the CD.  A clear coating of lacquer is used on CD’s to protect the aluminium layer which contains the digitised information.  When this lacquer coating has corroded the aluminium layer is exposed to the air and will thus oxidise.  This oxidisation means that the reflective quality of the aluminium is impaired, and it cannot reflect the laser tracking beam.  Eventually the CD will become unplayable.

Such a breakdown can be spotted by a `bronzing’ effect on the CD which starts from the outer edge and gradually works its way inwards.  This effect generally starts on the label side of the CD.  Affected discs will eventually produce digital errors, especially in the last tracks.  CD’s track from the centre out and therefore the final tracks will be affected more than those recorded towards the centre of the CD.  The beginning of the breakdown of the digital information can be heard by a sort of `crackly’ sound when playing back the CD, not unlike the noises heard on a well-played vinyl disc.

This phenomenon is most prevalent in CD’s produced by the PDO pressing plant between 1988 and 1993.  It seems that a substandard lacquer was being used at this time. PDO pressings often have a yellowish tint which must not be confused with the bronzing effect.  For some reason disc bronzing does not appear to affect all discs in a particular batch. 

PDO produced discs for Hyperion, Pearl, Academy Sound and Vision, CRD, Archiv, Deutsche Grammophon, London/Decca and Unicorn-Kanchma among others during this period and most discs, but not all, will have the words `Made in the U.K. by PDO’ on the inner hub.  It is recommended that any discs in a collection which were pressed by PDO at this time are checked for the effects of bronzing every six months or so.

Compact discs showing breakage due to improper handling and damage from exposure to a heat source

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