Sand is a basic component of glass, and it contains metallic impurities that color the glass. While this is wonderful if the artist or manufacturer needs that color glass for their final product, it is often a problem. Artists long ago learned how to add metallic compounds and oxides to turn molten glass clear, and these techniques are still in use today. Whether a large manufacturer is making a batch of glass for commercial uses, or an artist is melting a small batch for a project, creating clear glass is the first step in manufacturing colored glass.
Once a clear glass product has been achieved, color is added to the glass by introducing various metal compounds or oxides to create color in the molten mixture. Many manufacturers have their own standard palette of colors, and their processes are well-defined. Artists generally have a vision of the finished piece they are creating, and they may need to experiment to get the colors they need.
Plates of glass for art are manufactured in large sheets, and the color is mixed through the entire batch of molten glass to ensure little color variation. An artist may have different needs, and they often partially mix their glass batch with metal to achieve the variations their design requires. Both of these methods are currently used to produce glass for artistic uses, but each of them requires knowledge of how different impurities will create color within the molten mixture.
Many artists who create with stained glass are not interested in mixing and melting their own glass, but they can still find a wide range of colored glass through online searches. Some manufacturers offer specialty color palettes in small batches, and others create unique colors for a fee along with their standard offerings. Glass products can be ordered online, and many are available through local glass craft stores or glass studios.