Higher melting glass?

[Zeldazog]

Hi

Wonder if anybody can help me here - I am working on some new stuff at Uni, and I am trying different ways of "grogging" clay (adding things like sand, or ground fired ceramic/rock/minerals to a clay body so it keeps its texture)

I want to try adding glass granules to a clay body, but clay, well, earthenware fires at 1000 degrees C, and stoneware fires above 1200

Clearly, normal glass, Bullseye, window glass, will melt out at this temperatures - depending how embedded into the clay it is, it could melt out completely, or it could turn into a glaze.

(Okay, I know technically, the melting point of even soda lime glass is higher than 1200 degrees, but its been done before, fired in clay, and it softens enough to run away - perhaps also to do with long firing schedules)

Anybody got any suggestions as to what I might try? Should I get out my pyrex and smash it up??

[Pat from Canvey]

All I can suggest is that you Google Obsidian glass and look at the description in Wikipaedia. I would think that you would be OK to incorporate glass into clay provided the particles were small enough. So rather than smash up your pyrex, try bottle glass first. Easiest way is to put the bottle in the oven and heat up to say 250 degrees C, then drop the bottle in a bucket of cold water. Failing that, put the bottle between lots of sheets of newspaper and hit with a hammer. Try keeping the sides of the paper closed so that shards of glass don't go flailing everywhere.

[Ian R Pearson]

You need silica/fused quartz. I have some spare tubing/rod you are welcome to if you email me privately your contact details and I will send a few lengths free.. Currently making crucibles for liquid sodium and we are talking of operating temps well in excess of 1000 degrees C. It goes straight in flame and one can plunge it in cold water no probs. It doesn't flow though, it more vapourises. Anneals at over 1100 ! I could demo at Flame off if anyone wishes a bizarre moment, not that anyone is bizarre here(!!!!?) nor would one want to make a bead from silica.

Ian

[Zeldazog]

All I can suggest is that you Google Obsidian glass and look at the description in Wikipaedia. I would think that you would be OK to incorporate glass into clay provided the particles were small enough. So rather than smash up your pyrex, try bottle glass first. Easiest way is to put the bottle in the oven and heat up to say 250 degrees C, then drop the bottle in a bucket of cold water. Failing that, put the bottle between lots of sheets of newspaper and hit with a hammer. Try keeping the sides of the paper closed so that shards of glass don't go flailing everywhere.

Hi Pat, thanks for that, not sure how easily I could get old of obsidian though..... as for the breaking up of it, that is no problem, one of the advantages of uni is access to equipment - including the big nasty frit making machine.....

Bottle glass has already been tried fired into clay, and it does tend to run and turn into glaze, which is not what I want.