Determining the quality of a CD brand – Quantity vs. Quality
Let me first say that this next section is not the final word on CD quality. This information was based entirely on research and Internet reports, not on original experimentation or my own personal scientific testing. The most important thing to come away with after reading this section is to realize that it really doesn’t make a difference which brand of CD you choose, it’s the maker of the actual CD. There are also several more factors that affect the storage of your data on CD. Those factors include intrinsic properties of the materials used in the disc’s construction, its manufactured quality, how well it’s recorded and its physical handling and storage. It would be easy to hope that CDs are all the same with the only difference being the price and the packaging. This unfortunately is NOT true. The reasons are unfortunate and it makes our lives difficult when trying to choose a reliable brand but hopefully I can guide you in the right direction. The archival quality of compact disks range from good to utterly horrible and there are several key elements that you need to investigate before buying. Read on…
First off, you need to know that the CD brand name is pretty much irrelevant. Most CDs are usually either generic, or generic manufacturers sold under known brand names. Let’s get this straight right out of the gate. Brand-names mean nothing. What you need to know is the actual manufacturer name. There are currently only around 12 actual CD manufacturers in the world. So as you browse the isles of your local techie store keep this in mind when you see all the brands available. When you’re buying a Sony brand you might be buying the exact same CD that’s packaged in a much lower priced brand. I’m not guaranteeing this but it is possible. Also, CD brands will sometimes change manufacturers so you might think that you are buying a reliable manufacturers CD and then next year you find out that they switched manufacturers! Ouch.
So the big question you are probably asking is “how do I know who is actually manufactured my CDs”? Very good question and one that I actually have an answer for. As you may have noticed the information is not readily available on your chosen brands packaging because obviously they want you to think that they’re producing the product. If it’s a good product it will further strengthen their brand name and obviously garner return business from you and others.
In the CD manufacturing world there is a standard called an ATIP code. (Absolute Time In Pre-groove) Without this information the CD cannot be used by a writer. The ATIP contains information about the manufacturer, but also technical information that’s used by the CD drive to write to the CD correctly. Mission accomplished! Hallelujah! We found it! Well, don’t rejoice yet. There’s one small catch. See, the information is hidden in the CD data and it can not be shown via your standard CD player or computer. What you need is a special program designed to display this information. A quick search using the phrase “CD-R ATIP reader” will surely give you many options to choose from so you can quickly determine who is the real brains behind your brand. Some of the best manufacturers in the world are Kodak, Mitsui (now called MAM-A), Richo, MPO, Fujifilm, Tayo yuden, Prodisc, and Acer gold. Again, this list is not the word of god and opinions always differ but this list should give you a good start. For current information and discussion you can always visit the resources and forums sections of my web site at http://www.archivingdigital.com.
Now to the next big piece of the puzzle, the actual CD materials. Keep in mind that discussing the quality of CD materials is subjective, and that the quality of the CD-R also depends on what speed, and with what drive it’s written. That said, there are very important points to keep in mind that will affect the permanence of your CD data. Let’s take a look at the separate parts of a CD to determine what’s important and what’s not.
A standard CD structure includes the polycarbonate, the dye, the reflective layer, the protective lacquer layer and sometimes a protective coat. Without getting overly technical and buried in geeky blabber, let me give you a quick overview of the physical CD structure.
The Polycarbonate Layer
The polycarbonate’s transparency, dimensional stability, impact resistance, and freedom from impurities makes it an ideal base for both CD-ROM and CD-R discs. This layer is the basic foundation on which all other layers are built. The polycarbonate is also what holds the stamped shallow groove called the wobbled pre-groove. The pre-groove provides tracking and timing information (The ATIP code mentioned earlier) for the recording laser in a continuous spiral. It ensures that data is recorded at a constant rate. The polycarbonate layer has little to do with the archival quality of the CD.
The Dye Layer
All CDs contain a photosensitive dye layer where your data is stored. This is the area that gets “burned” (as they say) when you store information on your CD. As far as archival CD quality, the dye is very important in properly storing your information. The first factor that affects the quality of the dye layer is responsiveness to the writing laser, so cleaner, better defined pits are created. Cleaner pits means fewer errors and more accurate data.
The estimated life-span of the dye is very important since we are concerned about archiving our photos and there are two factors that we need to consider when choosing. First, the sensitivity to light (sunshine, ultraviolet, incandescent, and fluorescent light) is important because this will cause the dye to breakdown and become useless. The second issue that we need to consider is the accuracy of the data write by the dye.
Phthalocyanine Dye is currently considered to be the best dye on the market for light sensitivity. Other dyes are Metal AZO and Cyanine. Cyanine and AZO being the next best in line after Phthalocyanine due to the dyes ability to be less sensitive to light. Other factors that directly affect the dye layer are high heat, water and high humidity. So an obvious first step to properly archiving your important memories is to keep your CDs safe from sunlight and humidity and store them in a light tight case, closet or safe.
Now, one good question is “how do I know what type of dye is used on my CD”? Well, this time around it’s fairly complicated again and I think I have it figured out but things are always changing so who knows! From my research I’ve determined that Cyanine based CDs are usually green, AZO are blue unless matched with a gold reflective layer which appear greenish, and Phthalocyanine is pale green or yellow green when matched with a gold reflective layer. The aqua-hued advanced pthalocyanine is also in use. To complicate this matter further some manufacturers are beginning to add tinted substrates to make discs appear almost any color, even black. The good news is that the color of the CD does not directly affect it’s operation since the lasers do not detect color.
So to answer this question it’s best to contact your desired manufacturer or brand and request the information if it’s not clearly posted on their site. The dye is a very important element and choosing the proper dye is essential. As stated earlier phthalocyanine dye is considered to be more light sensitive but I’ve read that cyanine based dyes are better for storing more accurate data. So in theory if you plan to store your discs in a protective case and in a light tight storage solution then it might be better to go with Cyanine due to the fact that you will have a better initial write of your photo data. So I guess what I am telling you is that officially, the final word is still out. For more discussion, advice and news on this subject please view the forums at archivingdigital.com and strike up a discussion.
The Reflective Layer
After the dye process the CD is then baked to remove any residual solvents and the edges are “washed” to remove any dye along the outside edge of the disk. The CD is now ready for the reflective layer. The reflective layer is the area of the CD that reflects the laser as it moves over the disk. The light reflected is sensed by the laser and transmitted into information that ultimately creates your data, photos or music.
The change in light intensity changes every time the laser goes over a pit into the land area and vise-versa. The reflective material is made up of either silver, gold/silver alloy or pure gold. Gold/silver alloy is recommended for the most cost efficient and stable choice but if you have deeper pockets always choose pure gold archival CDs whenever possible to achieve the maximum archival ability. According to Kodak, tests have shown Kodak CD-R Gold Ultima, which uses a pure gold reflective layer, to have a life expectancy of 200 years. Other Kodak media using gold and silver alloys have demonstrated archival capabilities of 100+ years. This not a product endorsement because it’s just an example and information based on the best possible life expectancy for these disks. You can take that for what its worth.
The most important thing to come away with knowing is that gold disks, although they will cost you much more, have shown greater permanence in many tests and are the highly recommended solution for users such as ourselves that are interested in maximum archival time. Silver corrodes through reaction with sulfur dioxide, an environmental pollutant that can migrate through the disc with moisture causing the disc to reduce the reflection of the laser and resulting in the data becoming unreadable. Therefore, silver is a good solution but for longer term storage, it’s not the best choice for obvious reasons. Gold is obviously the best choice but is traditionally more expensive. For our purpose here I would recommend buying nothing but discs manufactured with gold reflective layers and ensuring that you have taken that extra step to preserve your data. You won’t even miss that extra $1.00 five years from now when those discs read like a charm.
The protective lacquer layer
The lacquer layer is one of the final manufacturing stages of the CD. Once the CD has been stamped, dye coated, baked, and coated with a reflective layer it’s ready to be protected. The CD is coated with a layer of thin lacquer and cured under ultra violet light to produce an extremely hard coating. Although some manufacturers provide different levels of protection and coatings, the lacquer layer does little to affect the overall archival quality of the media if treated properly. I would assume that most of us will not be handling our archived CDs on a daily basis so scratch protection is of little importance. It is helpful to know that it is there though. The lacquer layer can be subjected to various degrees of scratching and abuse and the underlying data will still remain readable. To ensure maximum life, your CDs should be handled with care. As an extra precaution some manufacturers provide an extra protective top coating that will ensure extra protection against the unknown. Keep this in mind when making your final decision between your manufacturers.
For those of you like myself that are accident prone, here are some suggestions for properly handling your CDs:
Always handle the CDs by the edge or center and avoid touching the non-printed side of the CD. This will minimize contact with the protective layer and subjecting it to scratches.
Never use a ball-point pen to label a CD. The recording dye layer is very close to the labeling surface. The pressure from a ball-point pen can damage this layer or over time the ink from the dye might bleed into the CD causing data corruption. Try using an archival quality felt tip pen to label the CD. (A non solvent-based felt-tip permanent marker) Recommended pens can be found with several good archival material companies.
Store the CD in a archival protective case away from heat and direct sun light.
Obviously, avoid bending or flexing the CD in any way. They are durable but they are not indestructible.
If the CD must be cleaned use CD/DVD cleaning detergent, isopropyl alcohol or methanol but a lot of time cleaning can do more harm than good. If a CD has become scratched try buffing the area lightly with a very soft cloth until the area is buffed out. Purchase of a good camera lens cleaning kit might be a good solution. Then use an absorbent cloth to blot it dry and avoid excessive rubbing. Never use chemical solvents to clean the CD even if they are provided in a lens cleaning kit.
Finally, remove light dust and dirt by brushing from the center out. Never wipe in a circular pattern! As I stated earlier though you should not have to worry about this if you write data to your disk and store it away. Hence the term “archiving”.
Next Post: We’ll discuss buying a burner and how to and where to store your CDs