This new plate is a positive, though it is sometimes called a "mother" shell. Yet again the two plates are separated, and the positive is returned to the bath. From this positive are grown the dies from which the records will be pressed-the final die, a negative, being known as the "matrix" or "stamper". (In practice, several stampers are usually made, depending on the number of records that are to be produced). This is then given a hard chromium plating.

For every record two stampers are required-one for each side. In each of these is now punched a hole, one inch in diameter, exactly in the centre; any eccentricity will cause the finished record to swing, with consequent distortion of sound. Next, the two centred stampers (or matrices) are mounted, face to face, on the platens of a steam-heated, water-cooled hydraulic press; the appropriate labels are placed on the centre spindles, and some six ounces of plastic material, pre-heated to a temperature of about 300°F., is placed between the stampers. Steam is now passed through the platens, bringing the temperature of the press up to about 330 °F., and pressure is applied. Over the 12-inch diameter face of the platens is applied approximately 100 tons of pressure, and under this the plastic melts and flows across the matrices.

Next, cold water replaces the steam, and the plastic is allowed to cool while still under pressure. Some half a minute later, the press is opened to reveal a gleaming new record.

This is now removed by the operator, who trims off the surplus plastic round its rim before placing it, protected by paper, on a special rack. The plastic from which a modern LP record is pressed is made from a co-polymer of vinyl chloride and vinyl acetate (in the proportions, 85-15). To this co-polymer is added carbon black to colour the record, chemicals to stabilize the plastic against degradation during the heating process, and a lubricant to prevent it from sticking to the matrix. The labels which identify the record (and its repertoire, artists, and copyrights on the music) are pressed into this plastic, and are not, as is often supposed, merely stuck on to it. Inspection From the beginning to the end of the process of production tests and examinations are carried out by trained personnel to meet the most stringent standards of quality. From the press, the finished record goes into the examination department proper, where one in every 200 records is played right through to make certain that it faithfully reproduces the original recording. Before it is passed into stock, every record is examined visually. In the case of Reader's Digest records, a second checking system, also elaborate, is operated by a specially trained staff.