Glass master

What is a glass master?

The glass master is the pressing die (nut) with stamper for CD and vinyl. The glass master is the actual pressing tool in the pressing plant. Glass mastering is directly related to the music production especially with the production process of physical sound carriers such as CDs and records . The process of producing a glass master is known as glass mastering. During glass mastering for a CD, the information from the premaster is transferred to a glass disc coated with a photo-resistant layer using a laser beam, similar to the process used to burn a CD-R. The disk has a diameter of 240 mm and a thickness of 6 mm.

It can also be provided with a metal inner ring to enable industrial processing. The carriers are specially manufactured for glass mastering and the carrier surface must be polished absolutely smooth, as even microscopic scratches on the glass carrier impair the quality of the glass master produced.

The resulting glass master serves as a template for the production of the stamper in the electroplating process. However, the light-sensitive lacquer layer is irretrievably destroyed at the start of the electroplating process, so that only the factory-specific stampers produced from it can be stored and used for the subsequent pressings.

Glass mastering must be carried out in a clean room that meets at least the requirements of class 100 (= ISO 5). Dust, pollen, hair or smoke particles can destroy the glass master during production. When the glass master is finished, these environmental influences can no longer harm it, but during production they can render it unusable.

Basically, the process is very similar to glass mastering for CD production. However, a stamp must be created for each layer containing data.