EMI only pressed black vinyl. They pressed all of Geffen UK's black vinyl releases in the early 1990's [1,2], at least the Nirvana singles from Nevermind and In Utero, while the British colored pressings and picture discs were pressed by Orlake. EMI also pressed the Simply Vinyl first pressings until late 2000, when the plant was closed down (Simply Vinyl then moved their vinyl production to Record Industry in Holland) . The site and equipment were taken over by Portal Space Records, later known as Vinyl Factory Manufacturing, and production resumed in January 2001 .
The matrix codes were stamped by the pressing plant, probably into the mother plates, and not by the mastering studios which cut the lacquers. They were stamped using their signature typeface, and were consistent regardless of which mastering studio made the cut. The only exceptions were mastering studio names or mastering engineer signatures. The mastering studios only wrote the catalog numbers and side information around the outer edge of the lacquers to keep track of them during the plating process, but this area is trimmed off of the stampers and never transferred to actual records . This means that the matrix codes only identify the pressing plant, and the mastering studios cannot be identified by the matrix code font or pattern, unless they signed the cut. Images 1-2 show two EMI matrix codes. The font and pattern is easily identified.
1. Come As You Are 12" (DGCT 7) side A matrix code
2. Nevermind (SVLP 038) side A matrix code
EMI owned Abbey Road Studios, and used it as their main mastering studio for the EMI pressing plant. The Simply Vinyl first pressings were cut by Abbey Road , but the Geffen singles seem to have been cut by Copymasters, later Masterpiece, judging by the mastering engineer signature in image 1. "Stu." is the signature of Stuart Hawkes, who worked at Copymasters/ Masterpiece from around 1989/ 1990 to 1996. Hawkes' signature can also be found on the black 12" and the picture disc, the latter has completely different matrix codes and was pressed by Orlake. Some of the other Nirvana records may also have been cut by Transfermation.