Borosilicate crown

Fig. 11. Index of refraction vs dispersion and optical classification of glasses. The shaded area indicates the region of glass formation. BaF = barium flint BaK = barium crown BaLF = light barium flint BaSF = heavy barium flint BK = borosilicate crown F = flint FK = fluorcrown K = crown ...

BODIPY 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene BK7 a borosilicate crown glass... 

Fig. 10. Contraction isotherme d un verre de borosilicate-crown, aprfes trempe, en lonction du temps (Daragan, 1951) H = 5 minutes...

Figure 1. Index of refraction versus dispersion and optical classification of glasses shaded area indicates region of glass formation M. Plexiglas is a methyl methacrylate Lucite is an acrylic resin. BaF, barium flint BaK, Barium crown Balf, light barium flint BaSF, heavy barium flint BK, borosilicate crown F, flint FK, fluorcrown K, crown KF, crown flint LaF, lanthanum flint LaSF, heavy lanthanum flint LaK, lanthanum crown LF, light flint LLF, very light flint PK, phosphate crown PSK, heavy phosphate crown SF, heavy flint SK, heavy crown, SSK, very heavy crown, TiF, titanium flint.

Optical Crown Glass. Any glass of low dispersion used for optical equipment (cf. flint glass). There are many varieties, their names indicating their characteristic composition, e.g. barium crown, borosilicate crown, fluor-crown, phosphate crown, zinc crown. 

Cracking also affected the hardness of the BK-7 borosilicate crown glass as shown in Figure 4. No median, radial, or lateral cracks were detected at 4.9 N. 

Figure 4. Borosilicate crown BK 7 data, (a) shows diagonal length, (b) shows hardness, and (c) shows P/d versus d.

Figure 5. Uncracked and cracked Knoop indentations in the BK 7 borosilicate crown glass at 19.6 N. Indentations should be spaced further apart for most testing purposes in order to avoid interference, (a) is a bright field and (b) dark field optical microscope illumination. The dark field photo reveals that some localized cracking occurs under the left indentations, but the extent of cracking is dramatically different. The cracked indentation is 7 pjn longer.

Table 1 has our HK values for 0.98 N (the customary load in the world hardness standards) as well as the manufacturers own data. The BK-7 borosilicate crown hardness at 0.98 N concurs since neither the manufacturer nor we applied a correction factor for optical resolution limits. In contrast, our hardnesses do not agree with the manufacturer s listings for the first three glasses, possibly since the manufacturer... 

The ISE curve parameters for equation 4 are given in Table 2. The plateau hardness at large loads is aj. Single entries are shown for the two glasses for which cracking had no effect on hardness. Two entries are shown for the three glasses that were sensitive to cracking. The uncracked borosilicate crown data did not fit equation 4 very well, so no a j parameter is listed and only an approximate estimate of a is shown. 

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