any ideas please

[Paul Schulz]

hi guys the blank is 230 X 10 mm spectrum glass i annealed for 2 hours at 950 F then slowly cooled but when i try to slump the piece i no sooner start to heat the kiln and pop it thermal shocks , the kiln is only up to about 150 dec this is the 3rd time . i refuse it and much the same happens
this is the annealing setting i am following ,,it is difficult to get it just right as my kiln is all manual ,,no control box
950 for 2 hours
50 degrees to 900 hold 1 hour
100 to 850 hold 1 hour
100 to 700 no hold
any views or tip would be welcome

[Laurie Spray]

paul.....
With your kiln there is no way to heat slowly which is what this piece needs. I would heat this up no faster then 100 degrees an hour to at least 800 degrees. It is a shame because it has a great look!

[Paul Schulz]

ah well,,,looks like it may be a very long day ,,,,,and an even longer nite,,,, ah an idea,,,after i REFUSE it yet again,,,ill try to get it on to the mould while still warm > hot. that way it will carry over some of the temp and won't have to start from cold ,,,,,,i have some nice oven mitts

[Brock]

That is a classic annealing crack. You're going to have to experiment with your controls to achieve the temps you desire. It can be done many, of us did it for years, some people still do it without a controller. Practice with an empty kiln.

Start with your switches on 1/2. Give it 15 min, record the temp. Turn it up to 1. Repeat.
Repeat.
Repeat.
And so forth.

[Kevin Midgley]

do what Brock said but time everything accurately with a kitchen timer. Wear it. Don't put it down somewhere and forget.

[Paul Schulz]

thanks for the reply guys and as usual very helpful ,,i have some 10 mm float glass laying around the studio some where ill try a piece of that i think ,,,,i use a kitchen timer now ,,,my wife laughs at me when i carry it around,,, still all in the interest of art ..,,makes one think how people use to make great glass work in the good old days

[Kevin Midgley]

they used a sand clock......

[Haydo]

At least you are miles ahead with the timer going on. I used Brock's method for heat control for years with success after he suggested it. Hope you get a controller soon because it's like having a dedicated slave. peace, haydo