Archived posting to the Leica Users Group, 2007/11/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 3:04 PM -0500 11/12/07, Chris Saganich wrote:
>Yea, the radiation does cause stress in the glass but that isn't
>what causes the color. The color is caused by electrons re-bonding
>to different sights after the ionizing radiation kicks them out of
>their shells. The electrons need a new home in the structure and
>that changes molecular bonding. If we were talking about a stable
>crystal structure then the UV trick wouldn't work, but because glass
>is amorphous and liquid it is easy to restructure the molecular
>bonding...just add heat at the correct temperature...the annealing
>temperature. The UV can only do two things to glass either
>photoionize or be absorb as heat. Photoionization is kicking an
>electron out of its shell, but that's how the glass became colored
>in the first place. UV B and C have enough energy to photoionize,
>which is 4eV for glass. UV A or black light does not have enough
>energy to photoionize so all the energy is absorbed as heat, thus
>photo-annealing. So any radiation with energy less then 4eV would
>work, the time and intensity would have to be longer. I suppose UV
>A would be the most efficient since it has the highest energy, just
>under 4 eV.
>Chris
>
Thanks, Chris. That makes sense.
--
* Henning J. Wulff
/|\ Wulff Photography & Design
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