This will turn solder and lead to a very dark color. The longer you leave it on before cleaning it off, the darker your piece will become. Contains nasty stuff like Nitric Acid and Selenium Dioxide, so be sure to use latex or other protective gloves at all times. Nitric acid will remove fired-on paints and stains from medallions, stained glass church-type windows, etc. Use with extreme care when darkening foil around such projects. 8 ounce bottle.