Matrix (record production)

For the first several decades of disc record manufacturing, sound was recorded directly on to the master disc (also called the matrix, sometimes just the master) at the recording studio. From about 1950 on (earlier for some large record companies, later for some small ones) it became usual to have the performance first recorded on audio tape, which could then be processed and/or edited, and then dubbed on to the master disc.

A record cutter would engrave the grooves into the master disc. Early versions of these master discs were soft wax, and later a harder lacquer was used.

The mastering process was originally something of an art as the operator had to manually allow for the changes in sound which affected how wide the space for the groove needed to be on each rotation. Sometimes the engineer would sign his work, or leave humorous or cryptic comments in the lead-out groove area, where it was normal to scratch or stamp identifying codes to distinguish each master.

The original soft master, known as a "lacquer", was silvered using the same process as the silvering of mirrors. To prepare the master for making copies, soft masters made of wax were coated with fine graphite. Later masters made of lacquer were sprayed with a saponin mix, rinsed, and then sprayed with stannous chloride, which sensitized the surface. After another rinse, they were sprayed with a mix of the silver solution and dextrose reducer to create a silver coating. This coating provided the conductive layer to carry the current for the subsequent electroplating, commonly with a nickel alloy.

In the early days of microgroove records (1940–1960), nickel plating was only brief, just an hour or less. This was followed by copper plating, which was both quicker and simpler to manage at that time. Later with advent of nickel sulfamate plating solutions, all matrices were plated with solid nickel. Most factories transferred the master matrix after an initial flash of nickel from a slow warm nickel electroplating bath at around 15 amperes to a hot 130 degree nickel plating bath. In this, the current would be raised at regular intervals until it reached between 110 A and 200 A, depending on the standard of the equipment and the skill of the operators. This and all subsequent metal copies were known as matrices.

When this metal master was removed from the lacquer (master), it would be a negative master or master matrix, since it was a negative copy of the lacquer. (In the UK, this was called the master; note the difference from soft master/lacquer disc above). In the earliest days the negative master was used as a mold to press records sold to the public, but as demand for mass production of records grew, another step was added to the process.

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