... , of high quality optical grade with over 60 percent heavy metal oxide, including at least 55 percent PbO. The compositions consist of ... , 33% quartz sand, 0.5% potassium nitrate , 0.25% Antimony Oxide and other additives is about 3.25%. The compositions consist ... , 27% quartz sand, 0.2% potassium nitrate , 0.2% Antimony Oxide and other additives is about 1.6%.This glass is ...