Slumping a very Small Bowl?
Hi Everyone, i hope you may be able to help, i have tried everything i can think of !
I have some 8x8cm moulds about 3cm deep that I am trying to slump 7x7cm squares in to make little bowls. It is 2x3mm layers of artista glass with a little extra glass in the middle of the design (just a couple of flakes or triangles).
I have tried slumping at around 707 C at 5 每 15 mins and slumps fine but has frosty or what I assume maybe stretch / scratch marks all around the top on the mould side - see attached. I have also tried many schedules ranging from that to 590 for 12 hours !!
I also tried firing in the mold on top of bullseye thinfire paper incase it was the kiln wash but same problem.
Do you have any ideas as to what I have done wrong ?
Whatever schedule I do from 706 down to 590 for however long it still does the same 每 no difference in amount of frosty scratch round the underside 每 a 7mm band round the top of the underside of the bowl. My schedule is:
2hrs 每 500 pass
1 min to 590 每 706 (tried various all same effect)
Hold 45 mins to 12 hours (tried lots of variations - have tried finding the lowest bend temp and holding forever)
1 min 每 540 hold 204 mins
2.45 hours to 480 pass
2.30 hours 每 360 pass
Any Ideas on what i have done wrong ? Thank you!
* The marks appear to be those caused by the bowl slumping and as the center goes down the edges slide down the mold to complete the slump. These can be minimized by keeping your slump temperature down. At 6mm I generally do not slump hotter that 1140 F. Tim
* Thanks, i have tried to hold at about 600 for 12 hours, left marks but didn't slump all the way down - would it be normal to hold for 15 hours plus ? Sounds expensive to run a kiln for that long for a few little ones.
* I have very little experience with Artista, so can only say that you need to soak significantly longer at the normal slumping temperature for larger items.
I do not think I will get much experience with Artista either, because Schott has stopped making it in Germany (and I think everywhere else). It was useful for its large format colours, but I guess there was not enough demand.
* I had some Artista a long time ago and tried to do a drop-ring vase with a fused blank. I never did get it to drop through; that glass seems to require a higher temperature and I just lost patience with it.
I've also done some tiny slumped pieces like you're attempting. Because there's less volume of glass, there isn't much weight to get them to slump. You'll probably have to go hotter than you expect to compensate for the size of your blanks and the type of glass. I wound up making my tiny bowls as single layers to get them to slump with smooth bottoms. My molds were stainless.
I've done night lights that were two layers (I only use Bullseye) and they required hotter/longer slumps too, due to size.
* Yes, Artista requires temperatures similar to float glass for forming.
* A suggestion:
Because the small bowls don't have enough mass to drop the short distance that you want them too, and to avoid the stretch marks created by the mold edge, create a large mold, adding to the outside of your mold at the edge. Create a mold that is twice, or more the diameter you want ot end up with, adding the smae radius, or close, that what the bowl is at the walls existing now.
Cut your glass larger than needd by double, center it on the larger mold, bend it at temps that you have previopusly had success with and after it bends cut to size, fire poiish if needed for the cut edges.
The problem is not with you technique, the problem is the parts are so small the earth doesn't suck enough to draw them down!!
the larger mold eliminates the edge lines also.