Attn. Glassblowers Don't be fooled by the imitation Gilson opal that is currently on the market. It won't work with glass because its made with plastic resin. We use this material with glass everyday and if you buy from us you will be getting the real deal, guaranteed Gilson opal and Pyrex glass are a match made in heaven!! Not only is this opal compatible with Pyrex but it holds it's color and fire perfectly.