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Frequently Asked Questions on Caring for CDs and Their Longevity

by Christopher Dicks, Assistant Audio and Video Conservator, Library and Archives Canada, Music Division

Whether it is a collection of e-mail from your children, family photographs and films or recordings - both personal and commercial - you want to store these digitized mementos properly so they can be enjoyed over the years.

This FAQ answers your questions about the CD as a long-term storage option, the life expectancy of a CD, the best formats to use, how to store and clean CDs correctly, and how to determine the cause when your CD won't play properly.

Can a CD-R be used as a long-term storage medium?

Yes, Compact Disc Recordable (CD-R) can be used as a long-term storage medium. The longevity of CD-R discs depends on the materials used to make the disc, careful and accurate manufacturing processes, correct recording practices, and proper storage and handling procedures. Also be aware that CDs are destructible. Scratching, marker ink eating into the disc, bending, separation of the disc layers and heating and aging can destroy a CD. Given all these factors, the lifetime ranges of CDs and DVDs under standard storage conditions (23°C and 50% relative humidity) are:

  • Read-only CDs (factory stamped): 5 to 100 or more years depending on disc manufacturing quality

  • CD-Rs (Compact Disc Recordable): 5 to 200 years depending on disc type and manufacturing quality

  • CD-RWs (Re-Writeable): 5 to100 or more years depending on manufacturing quality

  • DVD, DVD-Rs, DVD-RWs (Digital Versatile Disc, Recordable, Re-Writeable): Not much data is available for DVDs, but its lifetime is generally expected to be similar to that of a CD

Another factor to consider in terms of longevity, is the life or popularity of the playback machine. CDs and DVDs may survive for 100 years, but the technology to play them may disappear before you have changed your data to a new format. For example, 8-track tape players can rarely be found today.

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What are the best CD-Rs to buy?

CD-Rs have a metal reflective layer that is essential for the disc to function. The best reflective layer material is gold because it is chemically inert - meaning it will not react and degrade as other metals might. The second best layer is silver, which is more reactive chemically, but generally cheaper and currently more widely available. Mitsui, HHB, Apogee and Quantegy, among others, make discs containing gold.

Your first choice for a dye layer should be phthalocyanine, a light-green compound that is very stable in the presence of heat and light. Other dyes that are used, such as cyanine and azo dyes, are less stable. There are many manufacturers currently using the phthalocyanine dye in their discs. Discs with a phthalocyanine dye appear gold through the base (non-label side) when a gold metal reflective layer is present or very light green when a silver metal reflective layer is used. Discs with other dyes have a blue or green or bluish-green appearance.

The metal layer in a CD is very thin and susceptible to being damaged. It is also very close to the top surface of the CD. Therefore, good protection is necessary. Make sure that the disc has been made with an extra-tough protective layer in order to provide maximum protection for the metal layer.

Buying a brand name does not always guarantee a good quality product. Always test each package of CD-Rs by choosing a CD-R at random and recording and then retrieving the information from the recorded disc to see if that batch of CD-Rs is reliable. If possible, try playing the disc on different players/readers to see if the disc can be read on all of them. If the playback exhibits problems, this signals that it was poorly recorded. By using discs recommended by the manufacturer of your CD burner, however, you should be able to produce discs with low error rates.
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What are the best recording practices to use?

When CD-Rs are recorded, errors can result from the recording process itself. Fortunately, CD players or readers have the ability to correct these errors. However, there is a limit to their correction capability. Therefore, you must keep the amount of error as low as possible to ensure that your disc will play properly. In the past, 1x writing was ideal, and many professionals chose to stay under 4x. Today, many CD-Rs have been designed to record at a faster speed and may perform poorly at low speeds. Generally, recording a disc at around 4x produces the best quality recording. Silver-manufactured CD-Rs enable a faster recording speed; therefore, a user might decide to record faster to silver than to gold. However, the speed you choose must be in the range that your computer and software can provide data to the CD burner and the range in which the burner can record the data.

Your recordings onto a CD-R can be unsuccessful. Data are read into a memory buffer before being sent to the CD burner. A buffer underrun occurs when the memory buffer is empty, yet the CD burner is ready for more data; therefore, the CD burning process fails. "Burnproof" technology solves the problem of buffer underruns by commanding the burner to wait any time when there is not enough data in the buffer. The problem can also be reduced or solved by fine tuning the buffer size settings in the CD-burning software and by using a faster computer and a faster hard disk.
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How should I handle my CDs?

Do not touch the surface of a disc with your bare hands - handle it by the edges and the centre hole.
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What should I use to label my CDs?

Mark only the non-recording surface of the CD (the clear inner hub portion of the disc). Use only solvent-free, water-based, fine-tip markers, such as the Dixon Redisharp Plus. Their ink will not eat into a CD and destroy the disc layers over time. Do not use adhesive labels because they can warp the disc as they contract, unbalance the disc or chemically degrade the disc.
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What are the best conditions for storing my CDs?

Store discs in regular-sized jewel cases in a vertical position when they are not being used. It is ideal to store CDs in low light and cool, dry conditions that do not fluctuate widely. A good range for relative humidity is 20 to 50% and for temperature, less than 23°C. If every element (materials, recording, formats, etc.) is of good quality and stored within the proper ranges, then they are likely to last up to 100 years. However, if a disc is full of flaws including poorer materials or if it is stored in hotter and more humid conditions than advised above, failures may appear within five years. Thus, in less than optimal conditions, the best way to conserve your data is to transfer (or "migrate") your files every five years to another medium such as a computer hard drive or a CD-R.
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For longevity, is it best to store audio information on a CD-R as a .wav file or as an .mp3 file?

It is best to record your audio files as a .wav file. An .mp3 file is a .wav file in which some data has been discarded in order to reduce the file size. The computer chooses which data to discard based on what the listener will least notice. You might be able to “compress” an eroding.wav file into .mp3 format later on and end up with a reasonably good .mp3. However, because the .wav file has already lost so much when it was converted to .mp3, a further loss from the aging of an .mp3 might be catastrophic.

If given the choice between recording, onto a CD-R, a .wav file into the audio CD format (the same format as the audio CDs you purchase) or recording it as a data file (like any other file you would save), choose the data file. When audio CD format files lose data, the player attempts to either insert data from previous and following data, or to mute the audio for a moment if there are too many consecutive errors. Loss of data may translate into clicks and pops when the CD is being played. However, a data file has a third level of correction, which the processor performs, that can provide extra protection against data loss and problems signalled by muting, clicks and pops. Test .wav files as soon as they have been recorded on a CD-R to determine if anything has been lost.
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How do I properly clean a CD?

The safest way to clean a CD or DVD is using a compressed air duster. Never use compressed solvent dusters. The second safest cleaning tool is a soft, lint-free cloth. The third safest cleaning method involves using a soft, lint-free cloth and distilled water to remove strongly attached debris. Soapy water (use mild dish soap) can remove greasy debris such as fingerprints. If you use soap, rinse with clean, distilled water to remove any soapy residue. If possible, avoid immersing the disc in water. Liquid solvents, which may erode the disc layers, and detergents are not recommended.

When you wipe a CD, wipe from the centre of the disc outward in a radial direction (like spokes in a bicycle wheel) to limit the amount of problematic scratching that may occur. A laser may be able to read "around" a radial scratch on the disc surface, but a curved or spiral scratch could completely obscure parts of the disc and thus the data.
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Why isn't my CD player or computer reading my CD?

Many things (for example, dirt or other residue stuck to the surface) can disguise themselves as a CD drive problem. Sometimes properly cleaning a CD will alleviate skipping and even alleviate a lack of readability. Always examine the surface of a CD before inserting it into the drive or player.

However, do not rule out that a problem on a CD could be caused by your CD drive. When a CD spins, it needs to do so in a stable fashion, without wobbling. If the mechanism in the drive allows the CD to wobble, then the data can at times be too far away to be read properly by the laser. This wobble may cause the CD to skip or to be unreadable. Try to play your CD in someone else’s computer. If that computer can read the disc, then you know that the problem could be due to your hardware.

A dirty lens in the CD drive can also cause a CD to be unreadable. A professional technician should clean the CD lens; although, with some advice and proper tools, you may be able to do this yourself.

Your CD could also be unreadable because you are using an older CD drive. Certain older drives can only read older types of discs and may not be able to read the new recordable CDs and CD-RWs that you or others have created or bought. Newer drives may be more tolerant of errors or more capable of correcting errors than are older drives.
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What is the difference between a DVD and a CD?

The information given for handling, labelling and cleaning a CD is also applicable to Digital Versatile Discs (DVDs). However the manufacturing and formatting specifications are different: some DVDs have two data layers on one side while others have one layer on one side and another layer on the other side. Other DVDs have two data layers on each side. CDs have one layer on only one side. DVDs have a greater storage capacity than CDs. This capacity allows for better quality recordings.

The latest DVD player might be designed to read all pre-existing disc types including CD-R, but a player that was designed before DVD was created cannot play a DVD. While it is possible to design the latest player to play all digital disc types, most machines omit some disc formats. The consumer usually pays extra for each added disc format. When purchasing a player, make sure it can play a wide variety of formats.
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If you need professional conservation help, please contact the Canadian Association of Professional Conservators:

CAPC
c/o Canadian Museums Association
Suite 400, 280 Metcalfe Street
Ottawa ON K2P 1R7
Tel.: (613) 567-0099
Fax: (613) 233-5438
http://www.capc-acrp.ca/index.htm

Additional Resources

For explanations and diagrams on how CDs are made and how they function, visit these Internet sites:
 http://www.howstuffworks.com/cd.htm
http://music.bb.prodigy.net/musicb/prodigy.cgi?action=topic_display_page&topic=3676
http://www.americdisc.com/en/pool/detailpool.asp?cat=17
http://mitsuicdr.com/technology/manufacturing/index.html
http://www.unik.no/~robert/hifi/dvd/
http://www.cdmediaworld.com
http://www.psavideo.com/CD%20ROM%20Info%202rtf.pdf

A highly technical explanation of CD errors is available from Media Sciences Inc. at:
http://www.mscience.com/cdrfail.html

For further queries on various areas of conservation, please visit:
Canadian Conservation Institute (CCI) Internet site (English and French):
 http://www.cci-icc.gc.ca/

Science et patrimoine culturel, France (French only) at:
http://www.culture.fr/culture/conservation/fr/index.htm

Centre de Conservation du Québec (French and English) at:
www.ccq.mcc.gouv.qc.ca

"Conservation Online", Stanford University, USA (English only) at:
http://palimpsest.stanford.edu/bytopic/genpub/

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