Everybody thinks it is nonsense all that information that is written on each CD case, about recording and read speeds, color of the media, warranty and they end up buying the famous “spindles” of 100 CDs at USD 0.99 each at the newsstand. We wonder if the color of the media is a mere characteristic of each manufacturer.
First of all, it is necessary to make clear that the media that will work for you in all your tasks does not exist. You cannot look at a CD and tell if it is good or not just by its color being silver, gold, green or blue. For each work, recorder and reader there is a recommended media. It does not matter if the recording surface colors are the same or very much alike, but two CDs by the same manufacturer can be completely different.
A lot of technology hides behind the colors of the recording sides. We are going to particularize the way they are made and which the main characteristics of each of them are, for you to be well informed and not to trust when the pirate on the corner says that his CD is better because it is “GOLD”.
In the first place, opposite to what many people think, the material used in the constitution of the media does not interfere in its storage capacity. That story about not existing a 680 MB CD in a specific color is nonsense. In the CD this capacity is linked basically to the disk size, mainly the recording layer, and can store 21 minutes of audio, or 184 MB, 63 minutes of audio, or 553 MB, 74 minutes of audio, or 650 MB or 80 minutes of audio and 700 MB. Everything in average numbers.
This last one, also known as CD-R80, is a very special product that has been developed by TDK to help the software industry and, because it is difficult to find in the world market in general, it turned out to be an efficient way to restrain piracy in many countries, where these CDs are rare and expensive. Unfortunately it is not all kind of equipment that is able to record and/or read this media, because it requires special calibration on the read and recording speeds.
[nextpage title=”Inside the CD Media”]
Basically, all the CDs are constituted on a plastic surface, that can vary a lot from each manufacturer. This does not matter much to us, and it is necessary to know just if the kinds of plastic are harder or less hard, some more easily broken, others with characteristics that make it look opaque with time and etc. Fortunately, the great majority of manufacturers chooses good quality material, even because it does not make the production that much expensive. Even so, there are episodes of CDs left in the car that, with the excessive heat, give off corrosive gases coming from this plastic that damaged them, and the worst: damaged the CD Player’s reading head.
The CDs that guarantee longer durability are usually made of better quality plastic and less susceptible to weather changes. Less quality plastic, (usually found in cheaper media) are naturally more vulnerable to thermal dilatation. So, the simple act of putting the CD in a drive that heats a lot can reduce its lifetime in months and can make it not possible to be read in other units.
On top of this plastic, on only one side, it is put a layer that is sensitive to determined wavelengths. It is the recording layer itself.
On the blue face CD, this layer is made from a special material called cyanine. This material is a metallic compound with special electromagnetic properties which composition is not revealed by the manufacturers. Because it is commercial technology, we would probably have access to its components only if we paid for it. Cyanine has a predominantly bluish color (cyan).
On the gold, silver and green face CDs, this layer is formed by a variation of the compound cyanine, called phythalocyanine that can be more or less bluish, according to the concentration of the material basic compounds. Some specialists stipulated that CDs with phythalocyanine should be necessarily cheaper, because the cyanine concentration is lower and those CDs would be designed to the low cost market, but this is not true. What happens is that some of the original cyanine’s compounds have been substituted and others have been added to this new cyanine, for non revealed reasons, but it is connected to the durability and we will soon talk about it. The “low cost CDs” reputation created a culture that even nowadays can be easily detected, that states that the blue colored CDs are the best without any technical or scientific base.
Over this layer, it is applied the metallic reflective material. This layer can be made up of two different alloys: a silver alloy or a 24k gold alloy. Naturally, gold has more durability and less susceptibility to damages than silver.
The final color that results from the CD’s recording face is determined by the reflective layer and its concentrations.
The blue media is made of cyanine in high concentration with a silver-based reflective layer. The gold media and silver media are made of a phythalocyanine layer over a layer of gold. So, that old thought that silver CDs are made of silver come to naught. Some models take a specific proportion of aluminum in this gold alloy, that helps generating the resulting final color. Practically every silver media is made with gold alloy layers and the industry has not contradicted this statement yet, which means that there is not silver media made with exclusively silver reflective layer on the market yet.
Specifically in the case of the green CD it is necessary to know that it can be both made of phythalocyanine and of cyanine. Always with the reflective layer in gold alloy.
[nextpage title=”Inside the CD Media (Cont.)”]
In the figure below you can observe the scheme of layers on a CD. The drive reading head is there just to show which the reading side is.
The label layer shown in the figure can simply not exist on cheaper CDs, which makes possible to remove both the recording layer and the metallic layer when one sticks on and takes a label off the CD. Do not trust CDs with a very shiny gold or silver surface opposing the reading one. The big CD manufacturers insist on inserting adhesive layers with their name and information about the CD. A scratch on this surface, when it is not protected by any label, is a thousand times worse than a scratch on the reading side.
The first recordable CD has been produced to Mitsui by Taiyo Yuden, that developed an alloy of gold with cyanine resulting the green color. The process that produces the gold CDs with gold and phythalocyanine base has been developed by Toatsu Chemicals. But Verbatim developed the blue media, made up of silver layers and a cyanine layer. The silver CDs that only came on the market in 1998 were created by Ricoh and it consists of a gold layer over an advanced” phythalocyanine. This would explain the CD silver color in spite of a gold reflective base. Other manufacturers that appeared later on the market started producing silver media with the conventional phythalocyanine, but adding higher aluminum concentrations to the reflective alloy. They are the silver/green CDs, cheaper than the similar ones with Ricoh technology.
There are two basic reasons for this variety of media found on the market. The first reason is that as each one of these compounds is a commercial compound, no company that wishes to produce CDs can use the technology of another company without paying for it. It seems to be logical to believe that no company will want to sell its technology to a competitor, as expensive as it may seem. So, if a new company wants to produce CDs, it has to create its own new alloys and layers, in spite of the fact that all of them are based in fundamental concepts that allow the generalization of cyanine and phythalocyanine to all of them.
Some CDs, such as the “Infoguard” by Kodak, have yet extra layers that have the only function of increasing the lifetime of the CD. These layers are basically systems that protect against scratches and some that take scratches to a certain depth. Nowadays most media (except the extremely cheap ones) have systems like this, not necessarily with the same technology, but with similar purpose.
The CD-RW have a completely different composition, except for the plastic layer. In substitution to the cyanine compound and the reflective metallic alloy it is put a kind of crystal that becomes opaque or translucent, according to the wavelength that goes through it. Those CDs reflect only 30% of the incident ray, what makes it impossible for them to be read in any CD drive (the conventional CDs reflect from 70% to 80% of the incident ray). The reading of the CD-RW is only possible in drives that have a circuit called AGC (Automatic Gain Control), that makes up for this “bad reflection”. The manufacturers never said anything about the composition of those CDs and anything you find about this special recording material is mere speculation.
[nextpage title=”Media Quality and Utility”]
As it has been already said, the media you are going to use in all situations does not exist. Each one of them works well in specific situations. Let’s start by describing the quality of each media according to the price, material and additional features by manufacturer and then see their utilities.
When we mentioned the CDs RW you might have thought that there are different prices for them, since US$ 5.00 up to US$ 30.00. And it is difficult to understand the reason for this whole variation: quality of the material. The cheaper the CD-RW, the shorter its lifetime and use potential, that is, the cheapest CD-RWs are not re-recordable anymore with the passing of time. The crystal that turns transparent or opaque according to the wavelength gradually loses that capacity with the recording/erasing of the CD. The more expensive CDs are made of crystals that involve more technology and will last more. We have tested a CD-RW by Ricoh that cost about US$ 8.00 and it allowed just 2 recordings. Today it is nothing but a regular CD-R! With the disadvantage of not being read in any drive. This 30% refection problem is another one that tends to get worse with time.
Also – and now we are talking about all kinds of CD – the cheaper the CD the worse its quality in all senses. The basic plastic material can go through the same problems we have mentioned and others, such as extreme hardness with time, which makes the CD easily broken or it can even twist it out of shape. This changing in shape can be also caused by the temperature, because the coefficient of thermal dilation of the metallic and recording layer is different from the plastic. Don’t you remember any CD-R that started to make noise after some time in the drive? That’s it, it happens because the metallic and recording layer dilates less than the plastic layer, making the CD to form a very discrete “U” shape that does not interfere in the reading, but can touch some part of the drive or even make noise while moving the air around it.
The color of the media can give us a hint of the use we can give a CD. The green dye media, for instance, was initially made of cyanine over gold. But the concentration of that cyanine is much lower than the one in a blue CD, for example. That makes this kind of CD skip tracks easily when used to record music, because it has lower recording surface density and is more reflective. If the laser beam does not touch exactly the recording track, that is much less dense in this case, the CD will skip tracks.
Nowadays practically all green dye media are made of phythalocyanine over gold. As the phythalocyanine is less bluish than the cyanine, the concentration of this material has to be much higher to result a dark green color, reducing the reflexivity and increasing the recording surface density, that makes the recording tracks denser and makes the CD skip less tracks.
When the phythalocyanine was released, the specialists ventured a supposition that the cyanine reacted with the gold, what has not been denied by the industry. That makes the CD with that combination (the first green CDs) to have a much shorter durability than the present ones. Beside, that kind of media got a bad reputation due to the first green CDs by TDK that did not have a layer against scratches as efficient as it should be, so, any small scratch made the CD to show reading errors.
It is also easy to understand that CDs with lower recording surface density are not ideal for higher speed drives. When a manufacturer recommends the recording and read speed of your CD, it does that based in calculations that involve the density of the recording and reflective material. Choosing a CD according mainly to its recording speed is fundamental when the recording is higher than 8x, also called critical speed.
However, the green media has the advantage of being more flexible to power variations than the others, making it more readable in different drives, mainly the older ones. Still today the TDK media is one of the best in this category.
The gold media and silver media are made of phythalocyanine layers over gold. As any media with gold reflective layer, these two ones have longer durability, because gold lasts more than silver. Another advantage is the fact that they work better in high read and recording speed Another advantage is that they work better in high read and recording speeds than the green ones.
This happens because the phythalocyanine used in those media is colorless and therefore has to be much more concentrated to make the gold reflective layer clearer than the gold natural color. In the silver CDs this reflective layer takes other metals in the alloy that make it less gold, mainly the aluminum that is found in cheaper CDs, but yet have predominantly 24K gold. There are obviously the bad manufacturers, that compensate the color by reducing the concentration of phythalocyanine and also reducing the gold from 24K to 20K, 18K and even 16K! It is the case, for example, of most silver/green CDs sold in Brazil for about US$ 1.00 each. As the addition of silver, copper and other metals in the gold alloy was not enough, they are practically 50% aluminum. Be careful! Besides being the worst in durability, those CDs are the less recommended for audio and read/recording in drives above 8x.
[nextpage title=”Media Quality and Utility (Cont.)”]
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 https://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.
[nextpage title=”Real Lifetime”]
Your new CD-R has two lifetimes: the lifetime after recording and the lifetime before recording. Usually the CDs without recording have a lifetime between 5 and 10 years. This reduced lifetime is due to the fact that the electromagnetic properties of the cyanine and the phythalocyanine are lost with time.
After recorded, the CDs can last 75 years, in the case of the green and blue media, 100 years when the media is gold and 200 years when the media is silver. However this data is given by the manufacturer, without any test made and they can vary a lot.
A silver media with aluminum, for example, lasts much less than half the time a silver CD without aluminum in its reflective layer. This can be applied to other metallic alloys and it is another important component that is not taken into consideration in the calculations that consider 75, 100 and 200 years and that deal with only the half-life of the cyanine.
One thing is for sure: to strictly follow the storage and maintenance conditions of the disk guarantee a considerable increase in its lifetime, either blank or after recording.
If we compare these warranties with the one of the pressed CDs, we will see the whole difference. A conventional audio CD has durability warranty between 10 and 25 years! In spite of being pressed and not recorded, the practically pure aluminum layer that is on its base starts to corrode faster. This can be observed if you compare, with the aid of a microscope, new music CDs to 10-year-old ones. You will be able to notice cracks between and across the tracks.
To end this part, we will remind you that, despite the very serious standardization relating the media, there is not any standardization relating the dimension of CDs and CD readers. Thus, a drive that does not read your CD but plays perfectly a pressed CD can give you a lot of trouble. The solution, in this case, is changing either the drive or the media.
[nextpage title=”CDs over 650 MB”]
For example: the CDs we find nowadays on the market are the 640 MB and 650 MB. We will hardly ever find CDs with more or less capacity, principally at accessible prices. When recording this kind of CD, we have a problem: how to do it?
First of all you should understand how data is recorded in CDs. It is recorded in sectors of 2352 bytes. From them, only 2048 are for data. The remaining 304 bytes are used for error correction and other things. Something extremely important to avoid disk read errors that are usually solved with the retry command, mainly if your media has high rates of block read error (BLER).
CDs recorded in this format DATA + CRC + INF are also called Mode 1. It is due to Mode 1 that you can only record 650 MB in a CD physically developed to 740 MB of audio.
A common error in those calculations is to assume that the manufacturer of your CD understands megabyte as the manufacturers of HD, that is, 1000 x 1000. Megabyte for the CD manufacturers is what it really is, that is, 1024 x 1024. It also explains the fact of 680 MB CDs on the Brazilian market. Those CDs are not of 680 MB! They are of 650 MB like any other, the difference is how the megabyte éinterpreted. In the case of those CDs it is exactly like the HD manufacturers do and those CDs are usually made by HD manufacturers, such as Samsung. It is even interesting, because there are CDs by Samsung with 650 MB and 680 MB labels. You may think they are different CDs but they are the same, but one is produced by a unit that also produces HDs and the other not. Summarizing, a 680 million byte CD has 650 MB and not 680 MB.
So, how can a 650 MB CD support up to 740 MB? Simple, just use the space reserved for CRC + INF to also record data, what gives us 80 MB more in a CD. CDs recorded like this are referred to as CDs in Mode 2.
Some software allow us to make this kind of recording, but not all recorders allow us to make it. Some recorders (most of the ones sold in Brazil) are programmed to record the CRC + INF in the disk, no matter the command of the software. It is necessary to be careful with this, because if the software does not know how to deal with this error and correct the size of the generated CD image, you can lose a CD and even damage your recorder. We have not seen any manual that made reference to that kind of characteristic of the recorder yet, and the manuals that inform they record CDs of up to 680 MB are usually making the mistakes described above.
CDs recorded in Mode 2 are not easily read in any CD drive and can show many errors from one computer to another, according to the configuration of internal devices. Before recording a CD in Mode 2 and saving some money with this procedure, you need to consider how much time it can cost you.
When recording CDs in Mode 2 use high recording surface density media, developed to high speed recording drives and record the CD in 1X. All this to prevent errors. It is needed to remember that this kind of recording ends up in reducing the lifetime of the CD, by the number of times the laser beam will go over the same parts searching for information that does not exist and re-reading sectors that became errors.
[nextpage title=”Other Media”]
There is CD media of other colors, either on the market or in research labs. One of those which appeared some time ago is the red media. This media, as any other that is not silver, gold, blue or green is nothing but one those four conventional colors with dye or different metallic alloy and even the result of a combination of dyes and a non-conventional metallic alloy at the same time.
Because they are rare, these CDs have gone through few analysis, but seem to be of inferior quality, mainly because they use dyes! Some manufacturers test copper-based alloys in substitution to aluminum in the silver CDs, what results an orange or even red CD, but basically has the same characteristics of the low quality silver CDs, but with higher durability and reflectivity that allows them to be easily read in different drives.