Rainbo Records was founded in 1939. Since May 2006, they have been located in Canoga Park, but they were located in Santa Monica while pressing their three Nirvana releases ; In Utero clear LP, Eight Songs For Greg Sage & The Wipers 4x7" box set, and Oh, The Guilt 7" single. When processing metal plates, they add an "R" to the matrix codes on 7" records and an "S" on 10" and 12" records, followed by five digits . They do this simply to keep track of the metal plates, except if the customer would ask them not to .
Laquers sent to Rainbo were often labeled "-R1", "-R2", etc., after the catalog number in the matrix code, where the numbers indicate the number of lacquers sent to Rainbo from the mastering studio .
Rainbo usually makes five test pressings, four which they give to the customer and one which they keep in their files for six months before it is discarded . More were made of the Eight Songs For Greg Sage & The Wipers test pressings, which must have been on request from the record label.
They usually pressed about 1200 records with each pair of stampers for quality reasons .