GB 1997 Machin Head Marginal Block 18 Light Grey No Value Courvoisier

GB 1997 Machin Head UM Block of 18 in Light Grey without Value. Gravure printing on coated paper without phosphor, perf 15x14, printed by Courvoisier of Switzerland.

Sheets of 100 stamps were produced in the light grey shade (along with sheets in deep green and flame) during the October 20, 1997 trial printings by Courvoisier. The number of sheets printed is unknown; however, because they were intended for technical evaluation and destruction, only an extremely small handful of sheets per colour are believed to have survived and probably one of the largest blocks in existence. No SG catalogue price is known.