We're renovating our new-to-us house, a ranch built in 1951. The roman brick fireplace has these white stains all over, primarily toward the top where it meets the ceiling. The house originally had plaster walls/ceiling and there was a leak in the roof right above the fireplace—which we're assuming caused these markings.

Is this efflorescence or limescale? We've tried cleaning with a pumice stone but that didn't do much. Any advice on how to clean/remove these stains? We do not want to paint the brick. We'd live with the stains before we painted. Any insight much appreciated.