How to avoid unwritable CDs and DVDs?

Solution 1:

I'm hoping people more familiar with the "material science" can address the data layer materials and the window of writability. But I can share some information on the identifiability aspect. Here are some readily identifiable things that might be thought to correlate with the writable period:

• Brand name:
  Manufacturing optical media is a very specialized business. Most of the readily recognized brand names (that are not media manufacturers), are just brand-labeled discs manufactured by another company, and the actual manufacturer can vary. Major brands with a reputation to protect will be careful to avoid putting their name on crap (although that can occasionally happen).

  Beyond that, the brand name, alone, basically tells you little about disc quality or characteristics. It's possible, of course, to find reliable information from a reputable source about a specific product.

• Cost:
  The writable period is essentially a side effect of the manufacturers' decisions focused on archival longevity. There is a relationship between cost and archival longevity, and the writable period is affected by a piece of it.

  Discs with longer expected archival life are more expensive to make because the materials are more expensive; the manufacturing process involves more complexity, precision, and testing; and there are higher reject rates.

  But there is not a direct relationship between cost and benefits, and not all of the cost goes into things that would affect the writable period. The dye layer material (selected for longevity), is the primary cost item that affects it. Other costs relate only to archival longevity issues, such as errors.

  Bottom line; how cost relates:

  • Extremely cheap discs won't have a long life. They will either lack the manufacturing quality and long-life materials, or they may be on sale because they are very old stock (which would eat into the writability window). So "extremely cheap" is a useful screening characteristic.
  • For expensive discs, cost isn't a reliable indicator of anything. You are better off focusing directly on the data layer material for an indicator of writable time.

• Product terminology:
  I've never seen a "best if used by" date. However, there may be labeling on the product packaging, in the manufacturer's specs or product descriptions, or in product reviews or testing reports. These sometimes describe the data layer, and often characterize the expected longevity. If someone else can tie unrecorded shelf life to archival life and data layer materials, these could be helpful clues.

  That said, consider the source when looking at the information. A disreputable company selling crap is likely to misrepresent the product, even plant fake reviews. Start with sources you trust.

• DVD+R
  I've seen one report claiming that DVD+R has longer archival life based on more robust error correction (a more degraded disc can still be read). Most reporting lumps DVD+R with DVD-R when reporting longevity. This error-correction argument would not affect how long the unused disc is writable.

• Data layer material:
  The data layer is a sandwich of a reflective surface and a dye layer. The reflective surface is normally silver or a silver alloy, gold, or sometimes a combination or alloy of the two. A number of types of dyes are used, sometimes in combination (a hybrid). The dye is a starting point; these are somewhat of a "secret sauce", with additives and proprietary formulations, and the manufacturers continually develop and improve them.

  The lasers used for DVDs and CDs are a different wavelength (color), so the dye colors used are different. The combination of the dye color and the color of the reflective layer produce the disc color.

  The predominant dye bases:

Cyanine dye is a weaker organic dye typically found in cheaper media. It is not a very stable dye, and can be hyper-photosensitive, thus diminishing it’s longevity. Many manufacturers use proprietary chemical additives to make more stable cyanine discs ("metal stabilized Cyanine", "Super Cyanine"). Although the additives used have made cyanine more stable, it is still the most sensitive of the dyes to UV rays. It generally appears dark purple for DVD media, and green or pale blue/green for CD media depending on whether the reflecting layer is gold or silver, respectively.

Phthalocyanine dye is an organic dye similar to cyanine, but with better adhesive properties, mostly use for CD-R. It is a natively stable dye (has no need for stabilizers). Phthalocyanine is more sensitive than cyanine to writing laser power calibration, meaning that the power level used by the writing laser has to be more accurately adjusted for the disc in order to get a good recording. CD-Rs usually appear silver, gold, light green, pale yellow/silver or green/silver (the dye base is transparent, so the color depends on the reflective layer and additives).

Azo dye is chemically stable and is the most resistant dye against UV rays. More modern implementations of this kind of dye include Super Azo. This change of composition from the earlier Metal Azo was necessary in order to achieve faster writing speeds. Metal AZO dye is a synthetic organic-metallic compound that results in a high reflectivity and decent lifespan due to the metallic content. It performs almost as well as a pressed metal platter. The dye is found almost exclusively in excellent quality media. Metal Azo appears blue or pale blue/silver (CD-R) or dark purple (DVD-R/DVD+R). Azo dye CD-Rs are dark blue. Super Azo is not as deep blue as the earlier Metal Azo.

Oxonol non-metallic organic and Metallic Dipyrromethene are two dyes specifically used in DVD media.

There are many hybrid variations of the dye formulations, such as Formazan (a hybrid of cyanine and phthalocyanine). Formazan is light green and the disc appears green/gold with a gold reflective layer.

Besides the dyes, there are many types of additives and exact formula modifications made by manufacturers to achieve better results. While a lot of information regarding dyes is available for CD-R, the DVD media information is more guarded. Most DVD manufacturers say something simple like “AZO” or “organic” as the dye base, so some of this is left to educated speculation (even the researchers at NIST have to do this). Quite a few DVD dyes are likely amalgamations of two or more dyes, similar to Kodak Formazan CD-R dye.

Unfortunately, many manufacturers have added additional coloring to disguise their unstable cyanine CD-Rs in the past, so the formulation of a disc cannot be determined based purely on its color. Similarly, a gold reflective layer does not guarantee use of phthalocyanine dye. The quality of the disc is also not only dependent on the dye used, it is also influenced by sealing, the top layer, the reflective layer, and the polycarbonate. Simply choosing a disc based on its dye type may be problematic.

The above is a composite of text lifted from The Digital FAQ, Wikipedia, and CD Media World.

So the data layer material is at the core of the writable period limitation, but its characteristics will be influenced by the exact formulation of dyes and additives. This can't be reliably determined from the disc's appearance, and probably not precisely from the manufacturer's description.