Studio Acrylics Phosphorescent Gels absorb the natural or artificial light and re-emits it in the darkness. These gels are slightly tinted so that the colors may be recognized in daylight, with the exception of the Colorless Green Phosphorescent Gel. For best results, apply the gels thickly, with a painting knife. They are a part of the Studio Acrylics range of auxiliaries, designed to widen the realm of creative possibilities when painting with Studio Acrylics High Viscosity colors. Studio Acrylics Auxiliaries can also be used in Mixed Media applications to further expand creative possibilities.100 ml tubes. Conforms to ASTM D-4236. AP certified.