Steel Blue Opalescent is a glass with some unusual working characteristics. When this glass was first being designed, Bullseye put it through a multitude of tests including firing it to full fuse temperatures. In all of these tests, it emerged from the kiln looking like it did in its cold form. 

Steel Blue Opalescent does turn a shiny silver-gray at temperatures 1250-1400° F. At about 1500° F, the effect disappears and it reutrns to its normal color. -PDF article and tutorial originally printed by Bullseye Glass Co.