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6. Other Properties |
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6.1 Bubble &
Inclusion
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It is most desirable to manufacture
bubble-free optical glass, but the existence of bubbles to some
extent is inevitable. Bubbles in optical glass vary in size and
number from one glass to another due to the many different
compositions and production methods. The classification of bubble
content is established by specifying in mm2 the total
bubble cross sections existing in 100ml of glass volume. Inclusions
such as small stones or crystals are treated as bubbles. The bubble
classes are shown in Table 1. The classification includes all
bubbles and inclusions measuring larger than 0.03mm.
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Table 1 |
| Class |
1 |
2 |
3 |
4 |
5 |
| The total cross section of
bubbles (mm2 /100cm3 ) |
<0.03 |
> 0.03
<0.1
|
> 0.1
<0.25 |
> 0.25
<
0.5 |
> 0.5
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6.2 Coloring |
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Internal transmittance ( t ) of optical glass is
listed for each glass type. To express absorption, a column labeled
"Coloring" is provided in the catalog page. Coloring can be
determined by measuring spectral transmission including reflection
losses with 10 mm thick test pieces. The wavelengths corresponding
to 80% transmission and 5% transmission are given. For glass
types of S-TIH 53 , PBH 71 and LAH78 reflection losses are so large
that we used the wavelength corresponding to 70% in place of
80%.
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6.3 Specific Gravity d) |
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Specific gravity is the density value of
well-annealed glass referenced against pure water at 4 °C, with the
value shown to the second decimal place.
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