Archaeologia, Or, Miscellaneous Tracts Relating to Antiquity Volume 46, PT. 1 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1880 Excerpt: ...Monza, a sapphire; and many of the ancient reliquaries of fine crystalline glass mounted in gold were thought to be crystal. g. Waves. These coarser superficial and protuberant striae, visible to the naked eye, arose from working the glass at too low a temperature (Ex.30). h. Threads, or Strings. These names are applied to other permanent irregularities of surface, caused by cooled particles of glass dropping, during the process of blowing, upon the viscid and imperfectly melted sheet, and being unable to undergo fusion and incorporation.. Crystals. These consist of matter infusible at a temperature higher than that at which the rest of the glass solidifies, and are due to slow cooling during a too prolonged and tedious manipulation of the sheet. If separate, they are usually transparent, and, being embedded in the substance of the glass, are invisible to the naked eye; but, when aggregated, they form white elevated and opaque masses visible even at some distance, which under the microscope are resolved into agglomerations of crystals, of which the commonest forms are long needles, prisms terminating in tufts or secondary groups of needles, prisms whose outlines appear corroded and indented like snow crystals, beautifully regular flat six-sided tables with sharp angles, and other six-sided tables--sections of prisms possessing an appreciable thickness (Ex. 126, 127). The minute size of these crystals, and the impossibility of separating them from the glass in which they are embedded, renders it difficult to ascertain their chemical nature; but Reinsch, who discovered some apparently similar crystals in (modern?) glass, concluded that some at least were silica." It seems probable, however, that most of the crystals above described are either silicate of...