1 Zloty 1 in circle, Trial Strike Al

In 1958, the NBP was actively evaluating aluminium as a replacement alloy for its base-metal coinage, running parallel trial strikes in multiple denominations to assess die wear and striking characteristics before committing to full production. The "1 in circle" counterstamp distinguishes this from standard trial pieces and indicates internal mint classification rather than a denomination change — a cataloging convention used by the Mennica Państwowa during this evaluation period.

Surviving examples are almost exclusively from institutional collections that surfaced after 1989.