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<p>[QUOTE=&quot;desertgem, post: 992940, member: 15199&quot;]Quartzite is not the same as quartz. Quartzite is sandstone which has been transformed into an opaque rock. The largest quartz crystal of record was in Brazil and was 20&#039; long and weighed an estimates 40 tons. A lot of crystal balls could be made from that. Someplace in my Gem magazines I have a photo of 3 men standing on a12&#039; crystal in a mine in Mexico.</p><p><br /></p><p>It isn&#039;t unusual to find metal added to glass, as it give it color. The traditional red stained glass found in older structures was made by adding gold dissolved in aqua regia ( gold chloride)&nbsp; to glass. Iron give glass an amber yellow color, manganese a purple color, cobalt deep blue, copper a lighter blue, chromium green, uranium a yellowish color ( called vaseline glass) no longer produced for obvious reasons).</p><p><br /></p><p>Lead &quot;crystal&quot; glass is a rather ugly yellow tint until Nickel is added to give it a more accepted bluish violet tinge.</p><p><br /></p><p>Since ceramic glazes are basically a glass layer on the converted clay, the metals mentioned above can be used in glazes. Except I used copper in a reducing atmosphere to get red instead of the gold <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie1" alt=":)" unselectable="on" unselectable="on" />[/QUOTE]</p><p><br /></p>

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