Orientation of Iridised Glass

Iridised Glass – Which Side Up?

“One rule in using iridised glass is iridised down to fuse, up to slump”

You need to understand the conditions for the “rule" before applying it. Bullseye iridescent and Spectrum System 96 (made by the Uroboros method - not the stained glass) iridescent are not temperature sensitive in the way the other fusing ranges are. Both Bullseye and System 96 can be fired face up.  It is not yet (June 2019) known how Oceanside fusing compatible iridescent will perform when it becomes available.

The Wissmach luminescent and the other fusing glasses seem to be more temperature sensitive and so need to be fused iridised side down.  Avoid using Bullseye Thinfire in contact with the iridescence, as it sometimes reacts with the iridescence and creates pits in the glass.

Use the lowest practical temperature when forming with the luminescent face up. This avoids the partial or complete disappearance of the metal film that creates the iridescence.

More information on what causes the iridescence.

http://glasstips.blogspot.com/2019/06/iridescence.html