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HNelson
08-27-2005, 12:15 PM
Has anyone slumped boro plate successfully without the sharpest area of slump devitrifying? I have a 1/8" thick x 8 .250" diameter plate I am slumping down on to a mold of Luminar sheet that is covered with shelf paper. The final shape is a taco. In the center all the way down through the glass is devitifying. The shape comes out perfect. I've trie 3 times.
1) ran to 1320 degrees f slumped let sit for 10 min. shut off
glass did not devitrify but had pitty mold marks.


2) ran to 1290 let sit 40min shut off
glass with little pitting but got the frosty down the middle

3) ran to 1275 let sit 45 min shut off.
No pitting but the frost down the middle.

I'm wondering if I should run to 1200 let it sit to soak even heat ,then ramp qucikly to 1350 shut down(with no saok and open the door for a quick cool to the annealing temp...

Any thoughts out there.

Someone suggested doing away with the shelf paper and coat the Luminar mold with a colloidal alumina..

......I'm stuck between pits and frost.....

Thanks for your help.

Heather

Matt Hess
08-27-2005, 08:51 PM
From what I have read your on the wright track. A super fast ramp up and down is what is required to not get devit from what I understand. I think Scutt kilns are currentley working on a kiln to slump boro. Sorry I couldnt be more helpfull. I will try to find that info for you and post it.
- Matt

J McGhee
08-29-2005, 03:10 AM
from what i understand is that the fast ramp down should done with fans till glass is 975 then take the piece out and place it in another kiln that is at 950 and then let it ramp down from there. the guys at the eugene glass school were tellin me about them trying it. if u email them maybe they'll tell ya more. been about a yr or so, memory sucks

FredLight
08-29-2005, 08:47 AM
The devit on that particular situation is more likely caused by the glass moving at a temp too low.

Slump at High temp, hold a short time, crash cool to 1050, hold for 15-20 minutes, natural ramp down.

Your own trial and error will get you the ONLY right answer.Slumping is an art guided by books and advice, but only perfected with experience. But we still hope to be of help.

Boyce Lundstrom's 3 books and Graham Stone has one hard to find book, these are where I found all my info to start with.

The type of kiln you are using REALLY matters here too. Top element kilns will heat the glass quickly and unevenly, side fire kilns will heat the glass a little slower yet way more evenly. Side element are your best bet with this.

But what do I know?

G Brebz
08-29-2005, 02:02 PM
could you use a hand torch inside the kiln to just get rid of the frost.. just a thought i really dont know, might work though ---------GB

10FennyGlass
08-29-2005, 04:55 PM
i wanted to just try slumping wit a torch and throwin in a kiln