GB 1997 Machin Head Marginal Block 18 Deep Green No Value Courvoisier

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

Sheets of 100 stamps were produced in the deep green shade (along with sheets in flame and light grey) 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.