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Tin Bloom

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").

Like devitrification, 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 bloom.

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 products.

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Copyright 2005 Brad Walker.  All rights reserved.

Adapted from posts on the Warm Glass bulletin board.

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Copyright 2005-2006 by M. Bradley Walker.  All rights reserved.

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