Green’s Dictionary of Slang

(drugs) a combination of amphetamines and barbiturates or tranquillizers.

1980

E. Folb Runnin’ Down Some Lines 143: Terms that are used interchangeably to characterize a sexually attractive woman and a variety of drugs [...] silk and satin. [Ibid.] 254: silk and satin 1. Any combination of amphetamines and barbiturates.