What does the "hard-boiled painting" mean?
Hello! I would like to get an explanation what does the expression "hard-boiled painting" mean? I read "The great Gatsby" of Fitzgerald, and there is a phrase in the book which says: "I never saw this great-uncle, but I'm supposed to look like him - with special reference to the rather hard-boiled painting that hangs in father's office". I can get what "hard-boiled eggs" means, or what is a "hard-boiled guy". But... "hard-boiled... painting"??? Is it a sarcasm, or an admiration, or something else?