Tin
  Atomic Number (AN) 50
  Atomic Weight 118.7
  Chemical Symbol Sn (fron Latin stannum)
  Periodic Table Group IV, metallic
  Other elements in Group IV: carbon (C:AN=6), silicon (Si:14), germanium (Ge:32), tin (Sn:50), lead (Pb:82)
  Specific Gravity 7.3
  Melting Point 232
°C
Just like art glass, float glass (the stuff used in windows) is fire polished on its top side; the molten glass flows to solidify into a smooth flat shiny surface. But unlike art glass, the underside is smooth, flat and shiny too. How is this achieved? The process was invented by Pilkington, and relies on the sheets of float glass being extruded onto the top of a very big trough of molten tin. As the glass cools and solidifies, it does so against the smooth liquid surface of the tin, which is still liquid even when the glass has become solid. This gives us our perfectly undistorting windows and mirrors.
        The tin has a subtle effect on the glass. A tiny amount of it is absorbed into the glass structure on the underside. That side of the glass is more liable to devitrification, may not take enamels as well, and may be harder to fuse. So, if you want to use float glass as a base for fusing, then the tin side should be down against the kiln shelf, away from the fusing interface and partly protected from devitrification.
        But how do you know which side is which? The supplier won't tell you. You need a Tindicator or tin indicator. Here is a picture of a commercial battery operated Tindicator, retailing for around $A90 ($US50). It is a simple source of ultraviolet (UV) light.
        To determine which side of the  glass is which, take your (cleaned) float glass and the Tindicator into a dark place. Hold the glass at about 45
° level with your waist and shine the UV from under on it. See the sketch. If the tin side is down, you should see a slight bluish-white fluorescence. Turn the glass over and compare. Since the glass itself absorbs the UV light, the fluorescence only occurs on the side near the UV source. Some float glass fluoresces more than other varieties, depending on manufacturer, batch, and many other variables. Float glass manufacturers don't much care about it. Some people shine the UV on the top of the glass. Whatever you do, don't look directly at the tube.
Making your own Tindicator
It is not overly difficult to make your own Tindicator, if you want to save money. Here's what you do:
Disclaimer
Use of this information is strictly at your own risk.  I disclaim all responsibility for injury to yourself or others, loss of funds, or damage to any glass product you may make.

Float Glass?
Why would you want to use float glass? In a word, cheap. It also comes in many thicknesses. There are many options for creating a sparse colour palette with a float glass base, but the commonest is to use it in transparent products. I also try out 3D glass ideas in float before committing to more expensive glass.
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 Copyright 2004+ Arthur Sale
Last Modified: 26 December 2010