The variety of ways glass has been used is certainly due to the fact that it is a material that has been known and loved for thousands of years, and thus has received the attention of many innovative craftsmen. Glass is the product of a silicic acid (often from sand) and an alkali (often from soda and ash). The combined ingredients must be brought to a temperature of about 1100°C (2000°F) in order to form a melt. Colors are imparted to glass intentionally or unintentionally by the presence of metal oxides. Clear or colored glass can also be stained with silver nitrate or some other products that are fired into the surface layers of the glass. There are still craftsmen who are making glassware using some old glassmaking techniques.