This color intaglio was done after Thrall had met Jack Thompson, an independent music engraver and typesetter employed by the largest classical music publisher of the time, Boosey and Hawkes in London. Thompson and Thrall became good friends and exchanged work - a music-themed print by Thrall for a collection from Thompson of German music-note punches and technical engraving plates.
"Symbol Systems" is an experimental collaborative work by Thrall, utelizing intaglio techniques he had learned from Atelier 17 founder S.W. Hayter while at a summer workshop at Ohio State University.
Thrall uses a irregularly shaped plate and Thompson's music plates and a technical plate, along with engraving, soft-ground and aquatint, printed with a brown ink. The graphs in the upper left are printed with a red ink.