The "Port of Saint-Cast (1890)" refers to a famous Neo-Impressionist oil painting by French artist Paul Signac, depicting the coast of Brittany with vibrant colors and meticulous "Pointillist" dots, showcasing stillness through his systematic application of pure color, and now housed at the Museum of Fine Arts, Boston. 

Key Details:
Artist: Paul Signac (1863-1935).
Date: 1890.
Style: Neo-Impressionism (Pointillism).
Medium: Oil on canvas.
Subject: A seascape of the Brittany coast, part of a series.
Location: Museum of Fine Arts (MFA), Boston, gifted by William A. Coolidge.