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Old 03-31-2005, 06:45 PM
Dave Bross Dave Bross is offline
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Join Date: Apr 2002
Location: Archer FL(near Gainesville)
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Dave Bross is on a distinguished road
Yes indeed! A must read. I love his take on art.

Now, from Scholes "Modern Glass Practice":

"The softening point of a glass, defined by Littleton as the temperature at which a filament of glass of specified diameter and length, heated at a given rate, elongates under its own weight one millimeter per minute, is a definite physical quality. According to Lillie, the viscosity at the Littleton softening point is 4.5 x 10 to the seventh power poises, or log n = 7.65.

The Littleton method is illustrated on this page. The small electric furnace contains a vertical iron core, four inches in length and one inch in diameter, with a 1/4 inch hole drilled through it lengthwise and another small hole drilled two inches deep paralell to the central hole. This permits the insertion of a thermo element at a point opposite the center of the rod to be tested. The specimen is a round filament of glass, .50 to .75 mm diameter, varying not more than .05 throughout its length of 22.8 cm. This is suspended in the central hole in the core of the furnace with its projecting lower end opposite a scale ( my note: "scale" meaning a ruler), against which the length of the freely suspended filament can be observed. Length in mm is plotted against time in minutes in the same units, and when the slope of the resulting curve reaches 45 degrees the temperature at the observed time is accepted as the softening point. The softening point of a glass runs about 200 degrees higher than its annealing temperature. The range for the commercial glasses is from 500 to 800 Centigrade (900 to 1500 farenheit) ."
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