CD bronzing is a specific variant of disc rot

Disc rot

Disc rot is a phrase describing the tendency of CD or DVD or other optical disks to become unreadable due to physical or chemical deterioration...

, a type of corrosion that affects the reflective layer of CDs and renders them unreadable over time. The phenomenon was first reported by John McKelvey in the September/October 1994 issue of American Record Guide

American Record Guide

The American Record Guide is a classical music magazine. It has reviewed classical music recordings since 1935.Since 1992, with the incorporation of the Musical America editorial functions into ARG, it started covering concerts, musicians, ensembles and orchestras in the US.The magazine prides...

.

Affected discs show an uneven brownish discolouring that usually starts at the edge of the disc and slowly works its way towards the center. The top or label layer is affected before the bottom layer. The disc becomes progressively darker over time; tracks at the end of the disc show an increasing number of disc read errors before becoming unplayable.

CD bronzing seems to occur mostly with audio CDs manufactured by Philips and Dupont Optical (PDO) at their plant in Blackburn, Lancashire, UK, between the years 1988 and 1993. Most, but not all of these discs have "Made in U.K. by PDO" etched into them (see image). Discs manufactured by PDO in other countries do not seem to be affected. A similar, if considerably less widespread problem occurred with discs manufactured by Optical Media Storage (Opti.Me.S) in Italy.

PDO acknowledged that the problem was due to a manufacturing error on its part, but gave different explanations for the problem. The most widely acknowledged explanation is that the lacquer used to coat the discs was not resistant to the sulphur content of the paper in the booklets, which led to the corrosion of the aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 layer of the disc, even though PDO later said it was because "a silver coating had been used on its discs instead of the standard gold." Peter Copeland

Peter Copeland

Peter Michael Copeland was an English sound archivist.From an early age he had a deep interest in collecting old gramophone records and in sound recording. In 1961 he joined the BBC World Service as a Technical Operator in the Control Room at Bush House, doing recording operations on disk and tape...

 of the British Library Sound Archive

British Library Sound Archive

The British Library Sound Archive in London, England is one of the largest collections of recorded sound in the world, including music, spoken word and ambient recordings....

 confirmed that silver instead of aluminium in the reflective layer of the CD would react with sulphuriferous sleeves, forming silver sulphate, which has a bronze colour. A combination of the two factors seems likely because, as Barbara Hirsch of the University of California points out, the oxidation could only have occurred if the protective lacquer did not seal the metal film and substrate well enough.

There are also isolated reports of CD discolouring with discs from other pressing plants, but these do not seem to be as widespread and may be due to other reasons than the manufacturing error that occurred at PDO. In particular, colour changes that occur along with the visible disintegration of the data layer (i.e. holes) are not typical of CD bronzing, but should be considered CD rot

CD rot

Disc rot is a phrase describing the tendency of CD or DVD or other optical disks to become unreadable due to physical or chemical deterioration...

.

PDO also manufactured CDs that have an even yellowish-golden tint. This is due to a yellow dye in the disc and is unrelated to the bronzing effect.

As bronzing is a progressive effect that cannot be stopped, any PDO-manufactured CDs that are not yet showing any signs of bronzing by now are very likely safe.

Affected record labels

At the time, PDO was contracted by several record companies, many of whose records may be affected. According to a list compiled on Classical.net, these include Albany Records

Albany Records

Albany Records is an American classical music record label focusing particularly on contemporary classical music. It was established by Peter Kermani in 1987, and is based in Albany, New York.-External links:**...

, Appian Records, APR

APR

- In the context of organizations :*Agrarian Party of Russia, a left-wing political party in Russia*Alabama Public Radio*American Public Radio, now Public Radio International*Asia-Pacific Scout Region...

, Archiv Produktion

Archiv Produktion

Archiv Produktion is a subsidiary label of Deutsche Grammophon founded in 1948.The first head of Archiv from 1948–1957, was Fred Hamel, a musicologist who set out the early Archiv releases according to 12 research periods from 1. Gregorian Chant to 12. Mannheim and Vienna...

, ASV Records

ASV Records

ASV Records is a London-based record label set up by Harley Usill, founder of Argo Records, Decca producer and former Argo General Manager, Kevin Daly, and producer Jack Boyce, after Argo's parent company Decca was bought by Polygram in 1980. ASV stands for "Academy Sound and Vision"...

, Cala

CALA

-Geography:* Cala, a town and municipality in Huelva province, Spain* Cala Gonone, a civil parish of Dorgali municipality in Sardinia, Italy* A business acronym for the Caribbean and Latin America-Acronym:* Center on Animal Liberation Affairs...

, Collins Classics

Collins Classics

Collins Classics was a record label which specialised in classical music. It was founded in 1989.Artists who recorded for the label included Sir Peter Maxwell Davies, the Duke Quartet, choral group the Sixteen, Harry Christophers and Joanna MacGregor....

, CRD Records

CRD Records

CRD is an English record label specialising in recordings of classical music, based in Truro.It was founded in 1965 by Graham Pauncefort as an importer and distributor of specialised European and American recordings, and in 1973 become a recording label in its own right. The distribution activity...

, Danacords, Decca

Decca Records

Decca Records began as a British record label established in 1929 by Edward Lewis. Its U.S. label was established in late 1934; however, owing to World War II, the link with the British company was broken for several decades....

, Deutsche Grammophon

Deutsche Grammophon

Deutsche Grammophon is a German classical record label which was the foundation of the future corporation to be known as PolyGram. It is now part of Universal Music Group since its acquisition and absorption of PolyGram in 1999, and it is also UMG's oldest active label...

, Globe Style, Hyperion Records

Hyperion Records

Hyperion Records is an independent British classical record label.-History:The company was named after Hyperion, one of the Titans of Greek mythology. It was founded by George Edward Perry, widely known as "Ted", in 1980. Early LP releases included rarely recorded 20th century British music by...

, IMP records, L'Oiseau-Lyre

L'Oiseau-Lyre

L'Oiseau-Lyre may refer to:* Éditions de l'Oiseau-Lyre, French-Australian Music publishers* L'Oiseau-Lyre , an classical early music label owned by Decca Records since 1970...

, London Records

London Records

London Records, referred to as London Recordings in logo, is a record label headquartered in the United Kingdom, originally marketing records in the United States, Canada and Latin America from 1947 to 1979, then becoming a semi-independent label....

, Memoir Records, Pearl Records, RPO Records, Testament Records

Testament Records (UK)

The Testament Records label, based in Great Britain, specialises in historical classical music recordings, including previously unreleased broadcast performances by Arturo Toscanini and the NBC Symphony Orchestra and Solomon...

 and Unicorn-Kanchana

Unicorn-Kanchana

Unicorn-Kanchana was a British independent record label. Originally known as Unicorn Records, the name Kanchana was added later to distinguish the company from Unicorn Records of Montréal, Canada...

. According to user reports on the Internet, other affected labels are Ace Records (UK)

Ace Records (UK)

Ace Records Ltd. was started in 1978. Initially the company only gained permission from the label based in Mississippi to use the name in the UK, but eventually also acquired the rights to publish their recordings. When Chiswick's pop side was licensed to EMI in 1984, Ace switched to more licensing...

, A&M

A&M Records

A&M Records is an American record label owned by Universal Music Group that operates under the mantle of its Interscope-Geffen-A&M division.-Beginnings:...

, Big Cat

Big Cat Records

Big Cat Records is a UK record label. It launched around 1990 and originally specialized in industrial and noise-rock releases. Operated a US office in NYC for a few years. Purchased by V2 Records in 1996, at which point their roster became much more diverse in style...

, Demon, Island

Island Records

Island Records is a record label that was founded by Chris Blackwell in Jamaica. It was based in the United Kingdom for many years and is now owned by Universal Music Group...

, Some Bizarre, Utility, labels distributed by World Serpent

World Serpent Distribution

World Serpent Distribution was a British record label and music distribution house formed in the 1990s by David Gibson, Alan Trench and Alison Webster...

 (Durtro

Durtro

Durtro was a British independent record label, established by the British poet, singer, songwriter, and visual artist David Tibet in 1988, to publish his own work, and that of fellow friends and musicians. It was replaced by one of Tibet's earlier labels, Coptic Cat, in 2010.Nearly every release...

, Threshold House

Threshold House

Threshold House is one of several record labels created by Coil to release their own work and that of affiliated projects. Associated labels include Eskaton and Chalice. It is also the name for the ....

, United Dairies, etc.) and Zippo.

Preventing bronzing

Unlike other types of CD rot

CD rot

Disc rot is a phrase describing the tendency of CD or DVD or other optical disks to become unreadable due to physical or chemical deterioration...

, most of which are caused by improper handling and/or storage of CDs, bronzing is due to a fault in the manufacturing process and can therefore neither be prevented nor stopped once it has begun.

However, storage conditions certainly seem to contribute to the speed of the decay, as some bronzed CDs were already reported as unreadable in the mid-1990s, whereas others were still playable by 2011. As it was noted that CDs stored in paper sleeves were deteriorating sooner and faster than CDs stored in jewel cases, it is likely that storing CDs in an acid-free environment might slow down the bronzing effect. A minimum measure would be to remove the booklet and paper inlay from the CD's jewel case, though it might be advisable to store affected CDs in envelopes made of alkaline paper inside a box made of acid-free cardboard. Plastic or vinyl

Polyvinyl

Polyvinyl is a group of polymers derived from vinyl monomers.Polyvinyl may also refer to:* Polyvinyl chloride* Polyvinyl acetate* Polyvinyl alcohol* Polyvinyl Record Co., an independent record label...

 sleeves are not considered safe because the softening agents

Plasticizer

Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...

 in the plastic may lead to further corrosion; polypropylene

Polypropylene

Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

 sleeves are a notable safe exception. Similar measures are used for books suffering from acid deterioration.

Because the recording is in the polycarbonate

Polycarbonate

PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

, not the reflective layer, the IASA has pointed out that in principle it would be possible to split the sandwich and re-coat the polycarbonate with aluminium to conserve the data on the disc.

Customer support policy

When the problem became known in the early 1990s, PDO offered to replace any discs thus affected if supplied with the defective disc and proof of purchase, and pledged to re-press new CDs until the year 2015 if a customer notices the corrosion problem. However, after a change of ownership, PDO (now EDC - Entertainment Distribution Company) discontinued its helpline in 2006, and defective CDs are now no longer replaced by the manufacturer, even though some of the affected record labels continue to offer replacement compact discs.

Customers owning bronzed CDs should therefore attempt to contact the respective record company or its national distributor.

External links

• EDC Blackburn (successor company of PDO)
• IASA - International Association of Sound and Audiovisual Archives
• University of Washington Libraries: Resources on CD rot and bronzing
• BBC report on decaying CDs
• Article from American Record Guide
• Classical.net article, with (now obsolete) PDO replacement information
• Hyperion Records support page