4.1 These two test methods are provided for evaluating the quality of annealing. These test methods can be used in the quality control of glass containers or other products made of similar glass compositions, where the degree of annealing must be verified to ensure quality products. These test methods apply to glass containers manufactured from commercial soda-lime-silica glass compositions.
1.1 These test methods describe the determination of relative optical retardation associated with the state of anneal of glass containers. Two alternative test methods are covered as follows:
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| Test Method A—Comparison with Reference Standards | 6 – 9 |
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| Test Method B—Determination with Polarimeter | 10 – 12 |
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1.2 Test Method A is useful in determining retardations less than 150 nm, while Test Method B is useful in determining retardations less than 565 nm.
Note 1: The apparent temper number as determined by these test methods depends primarily on (1) the magnitude and distribution of the residual stress in the glass, (2) the thickness of the glass (optical path length at the point of grading), and (3) the composition of the glass. For all usual soda-lime silica bottle glass compositions, the effect of the composition is negligible. In an examination of the bottom of a container, the thickness of glass may be taken into account by use of the following formula, which defines a real temper number, TR, in terms of the apparent temper number,