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Permanence and Handling of CDs - A KODAK WWW site about CD-ROM and CD-R products



Dear Colleagues,

 

Kodak Professional has a www site on the Permanence and Handling of CDs at

http://www.kodak.com/global/en/professional/products/storage/pcd/techInfo/permanence.shtml .

 

This site includes information on

 

More About Permanence and Handling

 •

CD Types

 •

Nature of CD-ROM

 •

When is a CD's Life Over?

 •

How Long Can CD's Last?

 •

Nature of Writable CD's

 •

Safe Handling

 •

Storage Conditions

 •

CD Permanence in Perspective

 •

References

 

Each of these above listed documents has some very valuable information, which is revealing, and in some cases brutally honest. Kodak does not forget to promote their own product, which is to be expected.

 

I wish to highlight some of the details I have extracted for those whose interest in not to such a level so as to read the 10 articles in total.

 

A. CD Permanence in Perspective States the following:

 

1. Ensuring the permanence of CD-ROMs and writable CDs (and indeed of any modern information medium) is a combination of manufacturers' and users' responsibilities.

 

2. This publication has surveyed the currently available technology choices in CD media. It has explained the special handling and storage requirements of CD discs which arise from their physical nature as objects of plastic and metal. Beyond this, however, permanence of the information stored on CDs depends as much or more on sound archival practices than on the inherent long life of the discs. Users of CD technology, whether in a personal or professional context, are the critical links in assuring data survival in the long term. Master copies kept in appropriate storage and handled only when necessary may last centuries. Copies for use are likely to have considerably shorter lives. Therefore, a strategy of master discs from which derivatives are made for use is fundamental to success.

3. Another useful approach is to maintain data in more than one form or in more than one type of storage media, perhaps in analog form, if possible. In addition, keeping copies in different physical locations helps guarantee survival.

4. The principal fact of life for all digital storage media is the rapid obsolescence of hardware and software. Users of CD technology should be reassured by the long physical life of CD discs, but they must not lose sight of the need to maintain a viable path for migration of data to new hardware and software platforms. Digital storage media impose a strict discipline that human-readable records do not: their rapid evolution creates a continual progression of technology that cannot safely be ignored for too long. However, armed with knowledge of the physical nature of the media and of appropriate archival approaches, users of CD technology can have the best of both worlds--the functionality of digital media and a long life for stored data and pictures.

B. So, How Long Can CDs Last? States the following:

1. Leaving aside scratches, fires, floods, and peanut butter sandwiches and concentrating on the slow chemical changes that determine the inherent life expectancy of a CD, extensive accelerated-aging tests suggest that Kodak writable CD products, including Photo CD discs, will not reach a BLERmax of 50 for a period of around 200 years when kept in the dark at moderate storage conditions. This long potential life expectancy is mainly a function of the greater dark stability of the dye used in Kodak writable CD products. Considering that BLERmax 50 is still not an unreadable level of error, Kodak writable CDs have a very long life expectancy indeed. Similar research by the 3M Company shows that CD-ROM products made by them will not attain a block error rate of 50 per second for more than 100 years in moderate storage conditions.

2. Accelerated aging is subject to uncertainties, but it does rest on firm scientific footing. Behind the data is the simple assumption that raising the temperature causes the reactions of decay to happen faster--so fast, in fact, that they occur within a few months, rather than decades.

Readability, or When Is a CD's Life Really Over? States the following:

1.     Still, nothing lasts forever, and it's important to know what the inherent life expectancy of a CD disc actually is. As mentioned, life expectancy at moderate storage conditions can be determined by means of accelerated-aging tests, and most manufacturers provide such data to consumers upon request. To understand the test results, one has to know what was considered the "end of life" for test purposes and, of course, what the predicted life expectancy turned out to be. End of life for a CD disc seems a simple concept--when the disc can no longer be read, its useful life is over.

C. The Nature of CD-ROM Discs States the following:

1. The tendency of CD-ROM metallic layers to oxidize over time can be measured with accelerated-aging tests. Today's CD-ROMs from quality manufacturers have a predicted life of over one hundred years (in normal storage conditions) without danger of data loss because of oxidation.

2. The presence of obvious pinholes in the metallic layer is another undesirable feature.

3. However, physical damage from scratches or other kinds of mishandling is still a serious threat. Proper handling, including appropriate storage containers for CDs, is a vital contributor to CD longevity.

D. The Nature of Writable CDs States the following:

1. Both the reading and writing are done from the bottom side of the disc, through the full thickness of the polycarbonate substrate. This provides scratch resistance as it does for the CD-ROM, but there is a catch. It takes a fair bit of energy for the laser beam to make a "mark" on a writable CD. That's why scratches and especially fingerprints or dirt are much more dangerous to a writable CD BEFORE writing than afterward. The fingerprint, dirt, or smudge can scatter the beam of the writing laser, perhaps weakening it to the point where the mark it makes is too small or too light to be read. For this reason, extra care must be taken in the handling of writable CDs before the data is written.

2. Lightfastness of Writable CDs

Tests show that the writable CDs of some manufacturers can be affected by casual exposure to light (for example, by leaving a disc bottom-side up on a desk for days). This can cause the dye to fade and the contrast between marks and lands to disappear. The dye formulation in Kodak writable CD products, however, provides much superior lightfastness, and the risk of accidental damage is much lower. Nevertheless, as a general rule it is prudent to keep all writable CD products in suitable enclosures (acrylic cases, caddies, or other opaque enclosures) when not in use and never to leave them exposed to direct sunlight.

E. Do Not Fold, Spindle, or Mutilate: Safe Handling of CDs States the following:

1. The worst handling stresses for a CD are caused by severe flexing or application of a sharp point to the top surface. These actions deform the substrate, wiping out pits and causing areas of the disc to become unreadable. A sharp stylus--a ballpoint pen, for example--can cause compression of the polycarbonate substrate and the metallic reflecting layer in the area under the pen point. This can happen to both CD-ROMs and writable CDs, but the danger is more acute for writable CDs. The adhesion between the dye and the other layers in a writable CD is weaker than the interlayer adhesion in a CD-ROM, where no dye is needed.

2. Be Careful Marking and Labeling CDs

User-applied labels of any kind may unbalance the CD and make it difficult for the player to read. Also, labels may peel in humid conditions. Once a label is on the CD, however, it is especially important not to try and remove it. The act of peeling off a label creates a lever action that concentrates stress in a small area. Such stress can cause delamination, especially in a writable CD. If it is necessary to write on the top side of a CD, a soft felt-tip marker is preferable to other writing instruments, but with some solvent-based markers there may be a danger of the solvents migrating into the protective lacquer. So, if a CD must be marked, it should be done in a way that is approved by the disc manufacturer.

F. Storage Conditions for CDs States the following:

1. In general, storage temperatures for CDs should not be any warmer than about 25°C (77°F) when archival permanence is desired. Cooler temperatures (down to about 10°C or 50°F) will help ensure the longest possible life expectancy. Relative humidity conditions should be in the range of 20% to 50% RH for best results.

2. Cycling conditions, especially between extremes of temperature and humidity, can be dangerous to CDs. Although moderate temperature and humidity changes ordinarily do no harm, fast changes between very warm and wet conditions to cooler and very dry conditions might produce warping and distortion. The recommended maximum limit for temperature change is 15°C (27°F) per hour. For humidity, the recommended maximum RH change per hour is 10%. In practice, such steep gradients of temperature and RH are rare. The enclosures in which CDs are kept provide the first line of defense against such cycling, damping the rate of change in RH so that the CD inside its case or storage cabinet does not "feel" fast changes occurring in the outside atmosphere.

I trust that the information is if interest and value.

 

Regards, Laurie

 

Mr Daniel Lawrance [Laurie] Varendorff, ARMA

 

Consultant/Trainer/Tutor/Presenter: Records and information Management

Imaging and Micrographic Specialist with 25 years experience

 

The Varendorff Consultancy

The Australian Distributor for A&P International

Scanner & Micrographic Resolution Test Targets

Visit our www site: http://www.pressenter.com/~apintl/

 

ABN: 77 836 801 165

27 Ronneby Rd, Lesmurdie, Western Australia 6076 - AUSTRALIA

 

PHONE: +61 8 9291 6925 - MOBILE: +61 0417 094 147

EMAIL: Laurie.Varendorff@Bigpond.com