Glass is available in many forms and finishes and varies in texture, from slick window panes to cast glass with a texture similar to stone. We always recommend cleaning and testing as a first step. Generally, Oils can be painted directly onto glass. For Acrylics, mix 3 parts GAC200 and 1 part GAC500 and add the mixture to paints until desired transparency is achieved. Watercolors and Drawing Media can be applied over an appropriate acrylic preparation like Pastel or Watercolor ground. Recommendations are for interior use only.