How and why should I clean glass before firing it?

Cleaning glass removes problem-causing contaminants like glass-cutting fluid, oils, minerals, salts, dusts, fibers, sticker residues, pen marks, and fingerprints. If these contaminants are not removed from glass before it's fired, they may be visible in the finished glass and may even cause devitrification, the growth of crystalline structures on the glass. To learn about cleaning materials and procedures, you can read our short article, Glass Cleaning Basics. Also, our online education program includes a full lesson on glass cleaning.