The first stage of disc manufacture involves the creation of a glass master and then from that glass master, one or a series of stampers.
Data from the original client master is loaded onto a mastering system hard disk. The mastering software then compares the data to a variety of industry format standards (red book for audio CD, yellow book for CD-Rom etc) to determine whether the data has been correctly formatted. If the data is not correctly formatted it is rejected, as any disc created from this information will not play on the intended player (e.g. standard audio CD player).
Once the data has been verified as being to correct format, the information is transferred to a high quality glass plate, hence the name glass master. These glass plates are used repeatedly by the plant – continually repolishing the glass to make room for a new set of data, until the glass is worn below the minimum and discarded or recycled. (It is therefore impossible to receive a copy of your actual glass master!)
Once the data is etched onto the plate, a nickel stamper plate is created to form a robust image of the original data set, suitable to place in an injection moulding line. A reverse image of the stamper can also be taken, with a view to creating several subsequent stampers. Depending on the quality of the nickel stamper used, a single stamper can be used to replicate up to (approximately) 30k to 50k discs.
A comprehensive description of the glass mastering process is available at http://en.wikipedia.org/wiki/CD_replication
The technique is very similar for compact discs and single layer DVD5s. Higher definition and dual layer DVDs such as DVD9 will require a different stamper configuration.
Replicated CDs are mass-produced using an injection molding machine. Small granules of raw polycarbonate plastic are fed into the press while under heat. The liquefied plastic is forced under high pressure into the mold cavity, with the metal stamper forming part of the cavity. The plastic is allowed to cool and harden. Once opened, the disc substrate is removed from the mold by a robotic arm, and moved onto the next stage of production. The cycle time, the time it takes to "stamp" one CD, is usually 2–3 seconds.
This method produces the clear plastic blank part of the disc. After the metallic layer is applied to the clear blank substrate, the disc is then lacquered and dried. Optical tests are then performed on the disc in a final pass to search for surface defects and test reflectivity. A portion of discs are rejected, and the good discs passed onto metal spindles ready for printing.
When CDs were first manufactured, each stage of disc production took place in a different machine with the discs being manually transferred between each stage of production. A clean air static free environment was required, which added to the high cost of early manufacture. As equipment improved, the disc replication process has become more automated, with completed (but unprinted) discs being produced in a single pass through the molding line and attached finishing station.