But, back to the quality of the good silver and gold CDs, during informal and non-scientific tests made by north-american specialists, these CDs have proven to be the best for car CD Players, due to its higher track density and its reflectivity relation outside the tracks is lower. Among the best media for this purpose are Ricoh Silver and Mitsui Gold.

The gold-based media is more tolerant to temperature variation, which, again, is another positive feature for its use in cars. When we also have good plastic material, that has the same dilation coefficient (only in good quality CDs, such as Mitsui), it gets very difficult to lose data due to CD dilation/contraction.

The Maxell Gold media gained a detestable reputation through the Internet and mainly in Usenet some years ago. In April of 1997 the company announced that it has reformulated the compositions and production line and their CDs, from then on, would work much better. Actually, nowadays Maxell is one of the best Gold media on the market.

There are also calculations that determine the so called BLER, or Block Error Rate. You can find a variety of BLER recorders and media on the Internet, at http://www.digido.com/chart.html. A media with very high error rate per block cannot be used to simulate 700 MB CDs", for example, which we will see below.

A media with high BLER can show sound distortions that are completely unwanted and that many times remain unnoticed to most people. The higher the recording surface density the lower the CD BLER. It is good to remember that this calculation also includes the recorder used, that can be of good or bad quality, making an excellent media into useless material.

At last, we have the blue media, which is formed by a high concentration cyanine layer over silver. This kind of media is usually recommended for higher read or recording speed drives. For being basically cyanine and a colorless metal, it is easier to identify when one of these CDs is good quality or not, mainly after recorded, because the CDs that "simulate" blue through dye in the layer lose all those dyes during the recording and the recorded tracks get very visible and much clearer in the CD.

You can almost never trust the cheaper blue media, because they take a lot of aluminum (some up to 88%) in its reflective alloy and this reduces the lifetime in many years, in spite of taking higher temperature variations.

The blue CDs are also indicated for sound recording, but they are not indicated for use in car CD Players. For having a reflective layer composed by silver, its durability is much lower and much more metal is released from this kind of CD. The ones that have high doses of aluminum release even more metal (release only silver). This metal can accumulate on the reading head of the CD Player, what makes it wrongly read the CD and many times it does not even recognize that there is a CD there, refusing to eject it! If this happens in a car panel CD Player, for example, you will go through a lot of trouble to remove the CD from there.

Those CDs are also less tolerant to temperature variations and usually lose a lot of their lifetime when exposed to those phenomena. To choose a good manufacturer, that uses the plastic material plastic with the same or similar dilation coefficient is always good to keep data integrity and increase the disk's durability.

But the blue media also has its advantages. After the green media, it is the one which is less susceptible to errors due to power variations and takes them very well. If exposed to a source of different frequencies such as the sun, for example, it is not very probable that it shows errors comparing to other media, because the cyanine responds to less wavelengths than the phythalocyanine.

They are less sensitive to small scratches, even without special protection layers, due to the concentration of the cyanine and the high track density and these disks are usually recommended for backup. It is the best media for high speed recording and read.