NEW YORK — To mark the 10th anniversary of the Louis Armstrong museum in the modest brick house where he lived for 28 years, curators are unveiling one of the jazz trumpeter’s most unusual artifacts — a plaster mask that had been stored in a cupboard for decades.

Armstrong, who documented his career in unusual ways, had the life mask with a painted bronze-patina finish made in the 1950s. David Reese, curator of the Louis Armstrong House Museum, said it reveals creases on his forehead, bags under his eyes and scars on his lips from a lifetime of horn-playing.

Museum officials still aren’t sure who made the mask, but a photo of Armstrong proudly holding it alongside an unidentified couple may provide clues. Armstrong must have been pleased with it because there are photos showing it hanging in the house at the top of the stairs....