Glass Pro Putty is a fast-setting black colored stained glass cement designed for strengthening and waterproofing leaded glass panels. Unlike typical stained glass cement, which tends to be the consistency of pancake batter, this stuff is more the consistency of cookie dough. Some people find it easier to work with and easier to clean up after (with the help of whiting). It's a ready-to-use oil-based elastic compound that is easily applied. It adheres tenaciously to came and glass, expands and contracts with weather, and forms a tough surface coating while remaining permanently elastic. Apply at temperatures above 40 degrees F (4.5 degrees C).