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I have just opened my own Studio making stained glass but want to be able to make beautiful kiln fired glass pieces too. I was hoping someone could help me with some problems/questions about slumping float glass.

I have a top loading flat bed kiln and so far I have tried fusing small pieces of float glass to make simple coasters using copper sheeting inside. (two 2mm pieces approx 10cm x 10cm) I am still experiencing bubbling, and am trying to minimise this by slowing down my rate of firing, and finding the edges have fine "spikes" - is this because I am overfiring or taking the glass up to too high a temperature?

I am currently taking the glass up to 600°c at 275°c per hour, full up to 843 and holding for 13 minutes. Coming down full to 620°c, taking the kiln down to 425 at 90°c per hour and then down to room temperature at 200°c. This schedule has been trial and error - the 4th so far!

Secondly I have been asked to make some basic dishes for a wedding present (what a responsibility!) and would like some advice about a good firing schedule for this.

I want to fuse some float compatible frits onto a square of 6mm float roughly 25cm square. I guess I can use the same sort of schedule that I have been doing for my coasters, hoping to avoid the "spikes" on the edges of course.

My question really is about slumping the glass - how slow do I need to go up to temperature, what is the slumping temerature and how slow do I need to cool down at to avoid shock and devitrification? I have a plaster type mould and will be using kiln wash.

I appreciate that my questions probably appear extremely simple to most of you but any advice or help would be great. This site seems to be such a great source of support and help and I have been really impressed with the spirit of openeness that exists.

Thanks for your time and hope to hear from someone soon.

Nikki

I would not go higher than 775ºC or so. This should eliminate your spikes.

Nobody can exactly tell you just what speed you can heat up in order to slump. You will find that out the hard way if you break a piece. Your kiln will behave differently than mine.

I typically take 1.5 hours to go from 38ºC to 538ºC (100-1000ºF) when slumping. This may or may not work for you.

Bert

Hello Bert,

Thank you so much for your help - I am suddenly feeling much more smiley about things and will adjust my firing accordingly.

Kind regards

Nikki

I always found it's better to start low and work up Nikki, saves a lot of materials in the long run.

My schedule for fusing coasters 80mm square, 2 pieces 3mm float;

to 570 @ 400degC/hr
to 670 @ 50degC/hr -this is a slow squeeze to push out the bubbles.
to 810 @ 9990degC/hr

then down the annealing ramp which is basically a mirror of the up ramp, only slower;

to 570 afafp
to 370 @ 100degC/hr
end of programme -allow to cool in it's own sweet time

These are the temps I use Nikki but as Bert mentioned, your kiln is different to everyone else's.

You can get float compatible frit from Pearsons in Liverpool.

The spikes are from firing at too high a temperature.

As for slumping, I find that float starts to move at about 620degC but you have to do the test to see what works for you and your kiln, at;

http://www.bullseyeconnection.com/pdfs/ ... tes_01.pdf

It pays to pay attention to the annealing ramp especially with the tableware -you don't want the plate to crack when the bride puts something hot on it

Thank you Paul for your sample firing schedule. I am sure I will get much better results from my next firing.

As advised I will do some tests with slumping and will be very careful with the annealing of the "wedding stuff"!

Kind regards

Nikki