On using silver over the gold in Angel Gilding - you can get a wonderful 24 karat plus layer of gold if you double gild - that is, pour on two coats of gold. But, as Danny says, the gold does not stick very firmly to the glass. It's very easy to scratch or wipe off. By pouring a layer or two of silver over the gold, you make the mirror layer more durable, maybe more brilliant and certainly less expensive. On the open market these days a Troy ounce of silver metal costs about $6.00 and a Troy ounce of gold costs about $420 - one reason why Angel Gilding is cheaper than gold leaf.
To use a mineral light: Clean the glass on both sides. Turn on the light and press the lighted rectangle right up against one side of the glass. Look at the light from the other side - through the glass. If the color you see is milky white then you are holding the light pressed against the tin side of the glass. If the light you see is clear purple then the light is pressed against the non-tin - or non-contaminated side.
The light looks milky white on the tin side because all those little molecules of tin that the glass picked up from floating on melted tin when it was being made (if it is, in fact, float glass) are being bombarded by the ultraviolet rays from the light and fluorescing (like those algae in the ocean). But don't just sit and stare at the light. The ultraviolet wave length that makes this process work is not very good for you. Like the sun, a little is not a problem but too much might be.
And a small note of shameless self promotion - we have the mineral lights in stock at
www.angelgilding.com - we just haven't posted them on the web site yet - but if you want one give us a call. (Sorry, Mike)