Ashes and Diamonds (1958)
Ashes and Diamonds (Polish: Popiół i diament) is a 1958 Polish film directed by Andrzej Wajda, based on the 1948 novel by Polish writer Jerzy Andrzejewski. It completed Wajda's war films trilogy, following A Generation (1954) and Kanal (1956). The title comes from a 19th-century poem by Cyprian Norwid and references the manner in which diamonds are formed from heat and pressure acting upon coal.
More at Wikipedia.