http://glassmusings.blogspot.com/201...ive-glass.html

Photosensitive Glass
Here is a picture of an interesting process involving hot glass (blown) work. This could also apply to fused glass work although I haven't tried it.
Attachment 58553

Attachment 58554


This piece is a blown platter that is about 16" in diameter. The intent was to blow a rondel, a round platter that doesn't really have any dips in the center and almost perfectly flat. That is one of the ways they made window glass in the "good old days". Anyway, this one is pretty good for me. There is a slight depression in the middle which is about half an inch deep. The interesting part of this is that you use a special glass color which is clear, but photosensitive. Thus it does need to be kept in a special wrapper until you are ready to use it. You blow the blank and then anneal/cool it. The annealer shouldn't be opened much as the piece is light sensitive and will pick up some darkening, however it is a very large exposure time.



The photo above shows the blank after it came out of the annealer and ready for its exposure. I took a bunch of egyptian symbols as well as a photo of me and a colleague on horses at the Great Pyramids at Giza. I just taped these on the glass and even used a Sharpie to write my name and date on it. We had to work in a dark room with a safe light, just like old fashioned black and white photographic dark rooms.

This was then taken outside. A very strong ultraviolet light, the sun being a great source is needed to expose the blank, just like a photograph. We left it outside at high noon for 45 minutes as there was some brief clouds. Normally 30 minutes in bright sun should be sufficient.

This is then placed in a cold annealer, brought slowly up to working temperature (around 1100 degrees), and then annealed again. This sets the image on the blank. You can see in the top picture the color difference. There is an interesting color cast to the developed image and overall blank. The original blank was a very pale blue, and this developed piece is a medium amber color. It would take a lot of practice to figure out just how to make use of the coloring.

Overall, I was impressed with the detail you can obtain using this process. I don't think I'll do it a lot, as it does require special glass and a means to expose it, but it sure is fun to contemplate.