Experimental Studies on ‘Stains’ Formed on Polished Surfaces of Optical Glasses

It was observed through a phase-contrast microscope that microcrystals are grown on the AOYAKE layer freshly prepared by acid corrosion, if the layer is left exposed to humid atmosphere and then desiccated. The growth of the crystals is remarkably accelerated if the specimen is repeatedly breathed on and desiccated. When the specimen is breathed on to form dews on the AOYAKE surface, the existing microcrystals are seen to act as condensation nuclei. Crystals as large as 10μ in side length can be grown in this way. These microcrystals are, undoubtedly, the chief constituents of the SHIROYAKE.<br>As was reported before, AOYAKE layers prepared by acid corrosion on some kinds of glasses are cracked and come off when dried. The separation in flakes of the AOYAKE layer is described in detail.<br>Spectral analysis of the microcrystals, the flaked AOYAKE layer, the corrosive as well as the mother glass was carried out, and the ratio in number of metallic atoms such as Na, Ba, Pb, etc. to silicon atoms (boron atoms, in the case of LaK 13) in each was estimated semi-quantitatively. From this experiment, the following conclusion was derived: Microcrystals are some salts of the metals, the atoms of which have diffused out from the AOYAKE layer. The AOYAKE layer is different from the mother glass in that it contains almost no sodium and less di and tri-valent metals. The wet AOYAKE layer is believed to be, so to speak, a hydrated gel-like silica film (H. G. S. F.) with a little amount of di- and tri-valent metallic ions left in it. When dried, it is converted into a gel-like silica film (G. S. F.) by dehydration.<br>The existing data on the properties of H. G. S. F. and G. S. F. are summarized, and a tentative theory on the mechanism of the growth of H. G. S. F. is proposed. The crux lies in the explanation of the variation of refractive index in the normal direction to the surface, which, according to Doi and Tsunekane's experiment, is uniform throughout the AOYAKE layer (H. G. S. F.) and undergoes a sudden change at the interface between the layer and the mother glass.