It provided CMY colour mixing via dichroic glass plates. A plate of dichroic glass can be fused with other glass in multiple firings. That is, certain surfaces within the prism act as dichroic filters. Glass artists often refer to dichroic glass as "dichro". Instead of a metallic coating, a dichroic optical coating may be used. Artistic glass jewelry is occasionally fabricated to behave as a dichroic filter. Over 45 colours of dichroic coatings are available to be placed on any glass substrate. In permanent installations and some theatrical uses, colored glass filters or dichroic filters are used. In fluorescence microscopy, longpass filters are frequently utilized in dichroic mirrors and barrier (emission) filters. As with the VL5, a dichroic, "cold mirror" was used as the reflector. Laser ablation is also used to create pattern, removing selectively coating from dichroic filter. Pictures are made by overlapping up to four colored dichroic filters. The simplest, physically, is the absorptive filter; then there are interference or dichroic filters. This kind of dichroic device does not usually depend on the polarization of the light. Pentacenes have been examined as potential dichroic dyes.