Wednesday, September 29, 2010

Temperature Test - Color Follows Ion Exchange

The final test of my study demonstrates a chemical reaction described by W. A. Weyl, Coloured Glasses, ISBN 0-900682-06-X. He states that the surface exchange of silver ions with sodium ions in the glass begins at 752°F, but crystals of silver atoms, which transmit yellow light, don't form until higher temperatures are reached. Basically, the silver penetrates the glass even before we see any change in color. In this test 2 samples of glass were fired to 800°F and held at temperature for 20 minutes. The clay body of the stain was washed off and one sample was fired again to 1050°F and held for 2 hours. The upper tiles are the tin side of float and the lower tiles are Lamberts. Comparing these results with the previous test (which was also fired to 1050°F) reveals the role the clay body plays in the reaction. The purpose of the clay or ochre binder, besides suspending the silver oxide,  is to capture the resulting sodium salt, forcing more of the sodium ions present in the glass to exchange with silver.

REUSCHE 292465 (Amber H465)
REUSCHE 1382 (Orange #2)
REUSCHE 1384 (Yellow #3)

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