Help! - what am I doing wrong???

[Grody]

Hi

Done a reasonable amount of (self-taught) fusing over the last few years but now tip-toeing into slumping. Had OK success with shallow stuff i.e candle bridges, sushi dishes, etc - but now having dire results from first two attempts at a deeper square dish - see pics below.

The first attempt with Dish 1 (6mm fully fused) didn't go to a high enough temp so the base didn't drop to the centre of the mould, then re-fired it higher but found a thick edge around the base and a ballooned centre.

Dish 2 below (5mm fully fused: opal on Tekta) didn't do any better. Mould had 5 coats and was kiln-dried to 200c before use. Air holes were fully clear.

Slumping prog for Dish 2 was: 220/hr > 710 (30 min): AFAP > 480 (30 min): 56/hr > 370 (1 min): end.

End result:
- edges pulled-in around perimeter (cushion-shaped)
- thick edge around underside but with major ballooning of centre (see shadow from skewer used to show profile)
- underside of sides have pronounced texture (cellulite?)

It's not a good look and I'm clearly doing something very wrong - but what? Too fast, too slow, too hot, too cold. Your help would be appreciated!


1_Pb090973_500px by tjkniveton, on Flickr


2_Pb090972_500px by tjkniveton, on Flickr


3_Pb090970_500px by tjkniveton, on Flickr


4_Pb090974_500px by tjkniveton, on Flickr

[helbels]

I know nothing about slumping, but to be honest with you, if you hadn't told me any of the stuff above, I'd have thought it was really pretty!!!!!!

[hollergrafik]

is the hole blocked in the bottom of the mold? slower ramp will help too

[Lilley]

Looking at your mould do the sides come down to the floor all the way round?  If they do then you will need to stand the mould on some kiln bricks or some such leaving gaps between them so that you have a means for the air to get out of the void under the mould - if you don't then it won't matter that the air holes in the bottom of the dish shape are clear you still have an enclosed space that the air can't get out of easily and so will be prone to having the bottom of the dish not being able to slump properly because it can't displace the air.  If the texturing looks like devitrification then look at the temperature that you are going to along with the length of time you are holding at top temperature - you can get the same slump by either holding for a longer time at a lower temperature or going hotter for a shorter one - you might try the hotter and shorter end if it is devitting.  If it is any help the firing cycle I use for slumping is as follows: 100/hr to 650 hold 10 minutes AFAP to 516 hold 30min then 100/hr to 100 then off (which is quite a bit colder and shorter than you have been using).  I don't know why the edges are pulling in, unless it is because 710 is quite hot I think so maybe the glass is flowing a bit - I dare say someone else with more experience will come along and say.

[flame n fuse]

Hi, as already suggested, it does sound as if you are heating it a bit too quickly and taking it up too high. Have you looked at the slumping programme on the Bullseye website at http://www.bullseyeglass.com/images/stories/bullseye/PDF/TechNotes/technotes_04.pdf
Also, their instructions for using a steep sided cone mould could be helpful http://www.bullseyeglass.com/images/stories/bullseye/PDF/other_technical/bullseye_cone_bowl_mold_8943_tips.pdf

we routinely use lower temperatures than are suggested by Bullseye - but it could be that the calibration of our kiln is wrong.

[Dee Dee]

Still beautiful dishes, though!  The pattern is lovely!

[Zeldazog]

I think the maximum recommended slumping temperature is 700, and I slump between 660 and 680 usually.

As Flame N Fuse says, I am same, I now fire lower than recommended by Bullseye, but I think Kiln Bill is a bit way off in his calibration too.

The pulling in is probably because the glass is softening, and running down into the middle, hence the thicker bottom edge.  And I agree, also a bit fast, probably trapping air, as Lilley suggests, also stand the mould - allows air to flow, mould more evenly heated and hot air can escape.

I think the texture on the underside of the sloped bits look like its picked up the kiln wash texture, which again sounds like you've gone too hot.

Bullseye technotes are good, and if you look on Warm Glass UK site, I am sure they now show the recommended slumping temperatures from Bullseye which vary depending on depth of mould, etc

[Pat from Canvey]

I'm with Steph, I still think they're beautiful if not what you expexted.

[jammie]

me too love the colours!

[ruth]

I like it as well. Looks good to me.

Ruth(sewnthings)

[Grody]

Hi all

Thanks for the nice comments about Dish 2 - I really didn't expect that!

I'm keen to learn and so will be paying particular attention to the comments about temperatures, ramps, etc.

Just a few things to add to the details:
- the mould was up on 1.5" posts when it was fired so air/temperature access was as good as I could make it.

- the air vent holes are right in the corners of the lower part of the mould (see pic below) so could easily be blocked by the glass settling into these corners, thus leaving air under the glass centre with little/no exit, hence the ballooning. I'm going to drill (yep, VERY VERY carefully!) a new central hole in the base, but this mould was from WG and made by the main supplier for the whole of Europe so someone else must have had this problem before though?


Img_5175_500px by tjkniveton, on Flickr

- the rough texture to the underside of the sides isn't devit, rather micro-wrinkles in a slumping/sagging sort of fashion. (Sounds like the sort of appearance that's waiting for all of us towards the later stages of our personal bus journey!)

Thanks to all for your input.

PS - must post details of my self-made tool for hot shelf lifting - it might be of interest to others.