Tin bloom is a milky or hazy film on the
surface of float glass, which occurs when the glass has been
tempered, slumped, or fused. It only occurs on float glass,
which is made by floating molten glass on a molten tin bath, which
results in a coating of tin on one side of the glass (commonly
called the "tin side").
tin bloom is a serious problem because it causes the glass to lose
its transparency. However, tin bloom differs from
devitrification in several ways. Firstly, bloom forms only on
float glass and only on the tin side of the glass. Secondly, it
often occurs after multiple firings with float glass (commonly on a
second slump firing, rather than the initial fuse firing).
Using a devitrification spray will not stop the formation of tin
In general, tin bloom is caused by oxidation
of the tin. Firing tin side down will help prevent or minimize
bloom, as will avoiding long soaks during fuse firings.
Venting the kiln to 1000F/540C may also help. Since tin bloom
often occurs with new fiber kilns or fiber shelves it's often
helpful to pre-fire new fiber kilns or shelves with a prolonged soak
at around 1600F/870C to help drive all binders out of the fiber
Copyright 2005 Brad Walker.
All rights reserved.
Adapted from posts on the Warm
Glass bulletin board.