WarmGlass.com

Hi,

I have been checking the boards for a while now, and I learned an awful lot from you guys. But I could really use your help troubleshooting my slumping schedule.

I recently purchased the BE medium classic mold (#8723). This mold has a flat bottom and somewhat steepish sides. I did not think that it would be this challenging to use it!

After my first attempt,the bowl had a nice flat bottom but there were three big 'round bumps' (approx 1 inch W x 1 inch L x .5 in high) on the inside of the bowl (sorry no pix). I thought that these areas were due to the fact that the glass had not slumped properly. There were also a few places under the bowl that were rough (almost to the point of cutting skin) instead of being smooth like the bottom. I used the following schedule (BE glass, 2 layers):

300 dph to 1000 soak 25
600 dph to 1250 soak 25
Full to 960 soak 60
100 dph to 800 soak 0
200 dph to 700 soak 0
400 dph to 100 soak 0

I put the slumped bowl back in the mold, thinking that it needed a longer soak. I guess that I interpreted these results incorrectly as my second attempt yielded worst results: the sides crept towards the bottom, making kind of a fold over the bottom... I used this schedule:

200 dph to 1000 soak 25
500 dph to 1250 soak 45
Full to 960 soak 60
anneal

I have now flattened the bowl, and would hate to see history to repeat itself... for a third time! Hindsight being 20/20, I think that I fired too hot and perhaps too long.

Do you have any experience with this mold? What slumping schedule would you recommend?

BTW, I have a Paragon Fusion 7, and the top of the mold is perhaps 2 inches below the elements.

Cheers!

Lucie

Slow down and fire longer and lower.

Try 200 dph all the way to 1200. There's no need for a hold at 1000 on the slump unless you're working thick and are worried about getting enough heat into the glass. Look at the glass (after a couple of minutes at 1200) and keep checking it until you've filled the mold; you'll need to do this everytime you change something- set up, mold, even colors- until you learn what you can get away with. Take notes.

Slow down the anneal too- use BE's schedule, it works.

Have you got Brad's book?

Hi lmartine

I have used the same mold 4 times, with a 2 layer blank

My slumping schedule is (have changed it to F):

300 - 1100 - 0
105 - 1200 - 60'

Included 60' hold at the end in case I need it, but the slump has always finished when the kiln reached 1200.

It is slightly faster than Marty's, but the top of my mold is 4" away from the top elements. Have cracked a blank going at this rate and closer to the elements (one of those "I should be able to get away with this" moments), so now I am very careful - either lower rate or further away from the elements.

For slumps, I always set the controller alarm about 60/70 degrees before final temperature, and take a quick peek. It is really good to use a strong torch to cut the glare, one sees a lot better. Mine is an LED LENSER T5, small in the hand and very strong light.

I don't really understand about the rough areas under the bottom. Can only imagine these already being there before the slump.

Just wanted to share my experience with this particular mold (success due to the great posts on these board - my glass bible). The mold has a very nice shape. Bought the next size up to use in my bigger kiln, but haven't tried it yet.

Hope everything is working well for you

Best regards, seachange

Seachange,
If your piece has completely slumped by 650ºC, then you can achieve the slump at a lower temperature with a soak. Doing so should provide fewer marks on the bottom of the glass.
With your larger mould, the slump will occur earlier, because of the increased span and weight.

Many thanks Stephen, I'll introduce a soak next time, it is always good to get the firings a bit better each time.

I also use the ball mold, same diameter. It is a shorter drop and a simpler shape, these slumps are ready at 610C. Got the bigger ball mold for the larger kiln as well, but still have to try it.

These are things I do in the winter, when things are quiet, which is right now...almost too quiet

It rains, it is cold, the wind is howling, just the right time to work on something nice and new, with happy, bright colors.

Best wishes, seachange

Hi,

I also achieved a slump at 1200F. But not knowing exactly what to expect for in terms of definition of the bottom vs. the sides, I continued on to 1220F with a 5 min soak. There were a few wrinkles, but not nearly as bad as with my first slumping schedule so I will definitely slump at 1180F next time with a 5 min soak.

I say next time because... poor annealing this time (will soon submit another post to get your two cents)! The bowl went 'ping' yesterday afternoon, before I even had a chance to take a picture of it. At least I know what it sounds like now...

And I know how to slump successfully. Thanks for all your help!

Lucie

imartine,
If you can get a full slump in 5 minutes, you are firing higher than you need. You want the glass to move gently to the shape you require. The fewer angles on the mould the lower temperature you can use. I generally believe that you should take at least 30 mins to do the slump. With the cooler temperature, there are fewer marks left on the underside. A slow steady rise in temperature allows the whole of the glass to be at the same temperature when the glass is soft enough to begin moving.