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CD manufacturing
This is a brief overview of CD manufacturing, of those parts of the processes which are essential in determining the place of manufacture of a record. It briefly discuss the various steps. For more details, I suggest you read the document at Cinram (pdf), along with an animation at Acses Co., Ltd.  Pre-mastering "Non image ready" recorded music must first be converted to "image ready", that is, to CD-R (one-off, gold master) or 8mm tape. Nowadays, CD-R is the most common. The image ready CD-R is sent back to the record label to be tested and approved.  Mastering First, a glass substrate, a round disc of polished glass, is prepared. A liqiud called photoresist is spin-coated evenly on the glass, and baked (about 110ºC) for about 30 minutes. The glass substrate with the dried photoresist is called a glass master. The glass master is placed on a laser beam recorder (LBR) which is connected to a computer. The image ready CD-R or tape is loaded into the computer, and the music is recorded on the photoresist with a laser. The glass master is developed by spinning sodium hydroxide over it, so that wherever the laser touched, the photoresist washes away leaving a tiny pit, or digital information. The developed glass master is placed in a vacuum chamber, and a thin layer, only a few molecules thick, of silver (conductive coating) is deposited onto the photoresist. This is now called the metalized glass master (MGM), or the matrix.  Metal-plating: Father, mother, stamper The MGM is then electroformed, that is, placed in a tank of nickel sulphamate solution, and a layer of nickel grows on the silver. The nickel is separated from the MGM. The nickel is a negative image, called the father. Just like with vinyl manufacturing, the father can be used to stamp discs, but if damaged, the entire mastering process would have to be redone. Instead a mother, positive image, is created from the father by depositing a new layer of nickel to the father. Negative image plates for production, stampers, are made by depositing a new layer of nickel on the mother.  Injection moulding The stamper is mounted on a mould. Molten polycarbonate is injected into the mould, and compressed under high pressure. The mould is cooled with water, and the plastic solidifies. Depending on the mould, this process takes 5 - 10 seconds for each disc. It is at this stage the mould IFPI code is applied to the disc. A thin layer of aluminum is sputtered onto the side which contain the pits/ information, creating the reflective metal layer. This process is called metalization. A protective coating, a thin layer of sealant or lacquer is spin-coated onto the aluminum, and dried, or cured, with UV light. The disc can now be printed, the most common method is to screen print, with 1 - 5 colors, one color at a time. Higher quality offset printing can also be done, but this is a plating process.  Matrix codes The matrix code is recorded to the MGM by the LBR along with the music. So discs with the same matrix code have all been created from the same MGM. If huge numbers are needed, additional stampers can easily be made from the mother. These will all have the same matrix code, as it's impossible to change it as soon as it has been written by the LBR. It is, however, possible to add code mechanically on the metal plates. This will look completely different to the code added by the LBR. Often these letters or numbers added like this will be made out of several dots, instead of full lines. It is easier to make it look good like this. Unlike with vinyl records, code can be added to all plates, fathers, mothers, and stampers, as adding code to a negative plate will not make it stick out of the disc as it would on a vinyl record. Examples of this are the dotted 1:1, M1S1, or 1-1-1 (or other numbers) done by Nimbus, WEA Mfg, and EMI, respectively. Victor added full lines, this does not always look perfect. These numbers are there to keep track of the various metal parts created from an MGM. If there are two numbers, the first is the number of the mother, while the second is the number of the stamper plated from the mother. If there are three numbers, the father is first. In that case, different father-numbers identify different MGMs as an MGM can only be plated once. It does not necessarily mean it's a remaster, because the different MGMs can be made from the same image-ready (master) CD-R. If the numbers are added one-by-one during the process, they may not be on a straight line. This is particularly evident on Victor pressings. See images for examples. Another curious example is the South African Nevermind CD where they scratched over Sonopress.  IFPI codes Unlike with vinyl, the music is most often mastered by the same plant which is going to press it. However, sometimes it's not always so. As the matrix code only identifies the plant which mastered it, one have to look at the various mould codes which may be present to find out which plant pressed the disc. Mould codes are added to the disc by the mould itself, so they have nothing to do with the matrix code. They can easily be identified as they appear to be carved into the plastic. Various pressing plants have unique mould codes, but the industry standard is the IFPI code. IFPI (International Federation of the Phonographic Industry) is an organization which fights piracy as one of their main goals. One way to do so is to let pressing plants use IFPI codes on their CDs. There are two types of IFPI codes (also called SID, Source Identification), the mould IFPI and the LBR IFPI. The mould IFPI is enforced physically to the disc by the mould pressing the disc. It is placed around the spindle hole, and has IFPI and four (or five) alphanumeric digits. The two (or three, in case of five-digit codes) first alphanumeric digits identify the pressing plant. Discs pressed by the German Sonopress plant will always have IFPI codes startig with 07. We then say that Sonopress has an IFPI 07 repertoire. The last two alphanumeric digits identify the specific mould which pressed the disc. IFPI 0701 would mean it was pressed by mould 1 at Sonopress Germany. Several different IFPI codes may exist for a pressing. CDs pressed in large quantites are not pressed by one mould only, but several. One can compare the matrix codes to see if, say discs found with codes IFPI 0738 and IFPI 0793 where done at the same time or at different time. If the matrix codes are identical, as with the Pennyroyal Tea single (GED 21907), it was most likely one pressing done on several moulds, meaning they made several stampers from the same mother. If they are different, they are entirely different pressings. Other small differences on the discs may also occur from mould to mould, read "IFPI codes" on the Pennyroyal Tea document linked to above for some examples. The Pennyroyal Tea single is an interestig case because there is also a variation without a mould IFPI code. It was done at the same time as the IFPI variations, but on one (or several) moulds which didn't have an IFPI code. The reason is simply that Sonopress hadn't included an IFPI code on all their moulds yet. IFPI codes were first introduced in late 1993, so the presence of one tells you that the disc was pressed later than or during the end of 1993. For example, if you have a Nevermind CD with an IFPI code, you know right away that it isn't a 1991 first pressing. The other IFPI code is the LBR, or mastering IFPI. It's written in the matrix ring along with the rest of the matrix code. It identifies the equipment used for mastering the MGM, the laser beam recorder. It always starts with an L, and then three numbers or letters.  Gold discs The rumor about CDs detoriating may come from the first Phillips CDs in 1982, where the ink printed on the CD, or even the ink printed on the front inlay, reacted with the CD and made it useless. Now either the CDs are improved or another type of ink are used, or both, and a CD will in fact outlive yourself, as they're guaranteed to last for 100+ years. Gold-layered discs will last even longer than discs with an aluminum reflective layer, as it coats more evenly and reacts slower with oxygen. The higher fidelity associated with gold CDs is actually a result of the remastering process and not of the gold coating itself.
1. Manufacturing numbers on discs (Sonopress and Nimbus CDs) 2. Mechanical additions to matrix codes (clockwise: EDC USA, Nimbus, Victor, Specialty) Thanks to Cinram and Amazon.com.

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