Overcoming Surface Tension

The basic idea behind kiln-pressed glass is that we can defeat the surface tension and create thin glass by squeezing it from above using weights.  The basic setup looks like this:

Kiln Pressed Glass Setup

As shown, the glass is placed between two kiln shelves and weights are placed on top.  Small fiber strips placed in the corners act as spacers to prevent the glass from being pressed too thinly.

The concept is surprisingly simple but the results can be spectacular.

For a step-by-step example (including some important tips for success and firing schedules), click the “Setting Up the Glass” link below.


Kiln Fired Glass

 June Askew  Hi

I would like to ask a question.  I have quite a bit of glass that I would like to use. I got it from two glassblowers. The first lot has been broken up &

the colours are yellow, orange, red.  The others are green, blue, aqua all from Gaffer Glass N.Z.  The second lot is from a glassblower called Tina Cooper from Eumundi Queensland. There are about 3 large platters where the glass has various thicknesses. Colours, red, orange, yellow, blue.  I would have to break these up.  My problem is, would I have to make a dam 

to spread the thickness & if so, would I need a lot of heat?  I do have a

separate amount of broken clear glass from the first glassblower that I

could use to separate colours.  I also have scrap Spectrum 96 in clear

& colours.  Do you think I can use the glass from glassblowers without

problems?  I would like to make use of it.  However, I have been told that

my Evenheat PMC kiln should not be fired above 850degrees as the guy

who fixes kilns has several that have burned out from going too high.  I  had thought to make paperweights with the Gaffer glass.  Also, which colours do not work together so browns do not come into it?  Hope you can give me some answers.  The bowl looks very lovely, I am sure people would be attracted to it.  I have noticed one glassblower here seems to be stuck on

certain colours, it seems to make his work not too inspiring using a blue over & over again with drawings on.  Some people don't like blue in their homes though I don't know why.  I just like doing all kinds of colours.

Thanks for any help you can give. p.s. My tutor thinks Gaffer glass does vary in its coe.   Tosca

Kiln temps

Tosca -

EvenHeat PMC kilns are designed to heat up to 2000 F, or 1093 C.  850 C is 1562 F, plenty hot enough to accomplish any glass fusing project you have in mind.

You cannot combine glass of different COEs without problems.  There are ways to test - you can make an inexpensive polarimeter (run a google search on "make a polariscope" or "... polarimeter"), you can do freeze tests - again, search online, but Brad Walker's books give info on how to do that, too.

You can always contact the company to find out what COE their glasses are.  In order for glasses to be used together in any fusing or blowing process without the risk of stress fractures, the COE must be close enough together (within about 3 points - whihc is why Bullseye/Uroboros COE 90 and Spectrum/Uroboros System 96 can't be combined in fusing/casting projects) that the strains are resolved during the combining and annealing processes.

As far as color combinations go, you just have to experiment - combine the colors you are interested in using in test strips, fire 'em, and see what you get!

Happy Fusing!


Fused Glass, Wood, Beads, PMC, Ceramics

Usable and Wearable Art

Art for the Sake of Art

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