Cold Water:Ice Water Glaze Fit Test - CIGFNotesThis test is done to determine how well a glaze fits a clay body. Delayed crazing is a big problem and this test accelerates the factors that produce it. While many people feel that thermal expansion numbers from body and glaze are needed to match a glaze to a body properly, the real truth is that no matter what the numbers say, the actual performance of the glaze-body system gives the real truth. This test is a measure of that performance.
Compatibility between the expansions of clay and glaze are critical to ware strength and the integrity of the glaze layer. Crazed glazes can provide a channel for water absorption by a porous body and they can harbor bacteria. Shivering glazes can drop chips of razor-sharp glaze flakes into food or drink.
If a glaze does not fit this test provides a direction in which to move the thermal expansion. This test is especially effective on low fire ware and has the intrinsic value of subjecting the ware to the type of treatment it will receive in actual use. Note that although a glaze may pass this test, it may still fit poorly enough to weaken the ware. Strength testing can be employed to determine if this is the case.
Procedure100 Apparatus
-Boiler (sufficiently large to hold a sample of your water or a large shard and completely immerse it)
-Ice and ice water container (of similar size)
-Timer
-Dipping tongs
200 Procedure
-Prepare the ice water container with enough water to immerse the object(s) and with enough ice to bring the water to near freezing temperatures and hold it there for the duration of the test
-Select samples (or shards) of your ware that are representative of the varying glaze thickness, contours, glaze wrap-arounds and a larger flatter glazed areas
-Immerse the item(s) to be tested in the boiling water for three minutes
-Move them to ice water for three minutes
-Repeat three times
-Use a black marker to color areas of the surface and clean the ink off using methyl hydrate.
-Note any craze lines highlighted by the ink and any areas near edges that may be flaking off (shivering).
VariablesVal - Value (V)Enter CRAZ if it crazes, SHIV if it shivers. If the problem is barely
detectable, add a '-' suffix. If it is serious add a "+".
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