Wissmach Crystal/ Dark Blue (color code 96-30) is a Prisma blend in COE 96 kiln glass, deep cobalt ribbons running through paler transparent blue in a 3mm sheet, tested for fusing compatibility. Wissmach's name for the blend is Midnight Blue/Crystal.
Appearance A strong cobalt band runs down the sheet with softer periwinkle and near clear washes on either side, and the whole sheet passes light, so it glows on a lightbox or in a window. Fine seeds and small bubbles are scattered through the glass, typical of handmade rolled sheet. Midnight Blue is the first color in Wissmach's name for it and the more dominant, and the streaking is unique to each sheet, so no two are identical.
Striking Wissmach notes its Opaque and Prisma colors may strike to a deeper or denser shade after firing, so plan on the fired blend coming out a little richer than the raw sheet. Fire a sample chip first if the exact shade matters.
Working notes Wissmach’s recommended full fuse schedule for a 6mm project made from two 3mm layers: heat at 300 degrees F per hour to 1225 F and hold 30 minutes, then 600 per hour to 1460 F with a 10 minute hold, cool as fast as the kiln allows to 960 F and hold 1 hour, then 100 per hour down to 700 F. These numbers come from Wissmach’s current published firing guidance. They are guidelines, not guarantees. Kilns differ, so fire a small test piece first.
Reactions This blend is a copper bearing color on Wissmach's COE 96 chart. Fired in direct contact with a sulfur bearing color such as String of Pearls, Oyster Pearl, Honey or Gold Tone, it can form a darker reaction line where the glasses touch. Results vary by batch and firing, so test the pairing first, whether you want the line or want to avoid it.
Format and sizes Sold as a 3mm sheet in 8" x 10.5", 10.5" x 16" and 16" x 21" sizes. Choose your size from the options on this page.
Fusing and compatibility Tested compatible with other Wissmach COE 96 kiln glass. With glass from other makers, a matching COE number alone does not guarantee compatibility, so fire a test tile before committing a project.
More of this color Also available with a Luminescent coating .
Helpful downloads Wissmach COE 96 Kiln Glass Catalog
Technical data courtesy of the Paul Wissmach Glass Co.
Description updated: August 13, 2026
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