This 90 groszy Polish stamp was issued in 1955 as part of the country’s Six-Year Plan industrialization series. The design depicts a miner operating machinery underground, symbolizing Poland’s focus on heavy industry and coal production. The inscription “Plan 6-letni to 100,000,000 ton węgla w r. 1955” highlights the ambitious target of 100 million tons of coal. Designed and engraved by Czesław Słania, one of the world’s most renowned stamp engravers, it stands as an iconic piece of socialist-era philately. Highly valued by collectors for its historical context and fine engraving.