Blacksmith's waste

I believe the answer is:

slag

(Other definitions for slag that I've seen before include "Waste left over from coal-mining" , "Waste from ore refining" , "a girl who puts out" , "Smelted-ore refuse" , "Scum on metal - dissolute woman" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.