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Author Topic: thick bowl  (Read 1992 times)
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jackiesimmonds
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« on: February 12, 2015, 03:07:14 AM »

I recently slumped into a small bowl mould.  I used Bullseye, two layers 3mm glass.  I used the "slump" schedule for Bullseye which is ready-programmed into my Hobbyfuser - which has worked for dishes with a gentle uplift at the edges, just fine.  And for small, shallow dishes.

But the bowl-shape came out quite differently.  the mould is made from bisque, and has no base...I copied a little Bonny Doon shape, had it made by a friend. Straight, but sloping sides, down to a flat base which is basically the kiln shelf.

the glass slipped right down to make a nice flat bottomed bowl, which was what I wanted......but the bowl is really rather thick.   so thick it looks clunky.   Is this inevitable?  Or is there a way to ensure that the glass does not squish up and thicken?    The finished bowl shape is quite a bit lower in height than the sides of the mould.
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Pat from Canvey
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« Reply #1 on: February 12, 2015, 05:13:05 AM »

I don't know what you mean by Bonny Doon shape. I Googled and pictures of hammers came up. Can you post a picture? Are you saying that the base is thick or the sides or both. When using a drop out mold such as http://www.creativeglassshop.co.uk/product/32078/drop-out-ring-17-5cm-opening-6cm-fusing-mould.html you have to open the kiln at intervals to see if the bottom of the glass has reached the kiln shelf and when it does, what size you want the base of the bowl to be. If you want the sides and base to be less thick, you will have to make the glass stretch more by raising the mold a little highter. You also have to ensure that the glass doesn't slip from the mold by having excess glass around the circumference. This excess is cut of subsequently and the edges cold worked with a wet belt sander or flat lap. Nothing wrong with a bisque mold.

If I'd wanted a bigger bowl shape, I'd have used a wider drop out ring. You can see that I stopped the slump at the point where some of the glass had reached the shelf but not gone beyond that stage. Also about an inch and an half has been cut from the rim. This was the waste glass that stopped the vase falling off the mold.
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jackiesimmonds
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« Reply #2 on: February 12, 2015, 05:21:21 AM »

I am struggling with posting pics, Pat!   Until I get the answer to that, I cannot show you..I wish I could - I followed all the instructions for posting pics but I must be doing something wrong..anyway....it is NOT a drop-through mould.  The mould sits on the kiln shelf, and the hole at the bottom is so that the kiln shelf gives you a properly flat shape at the base.

Have a look here (you might find the entire website interesting...I did!)   http://bonnydoonfusedglasstools.com/what-are-bottomless-rings/

My bowl slumped beautifully into the mold, it has a lovely flat bottom, but the sides and bottom are now thicker than I would like.  the glass sides to the bowl are quite a bit shorter than the sides of the mould now.

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flame n fuse
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« Reply #3 on: February 12, 2015, 10:12:43 AM »

I've not seen these moulds before and it's an interesting website. What is your slumping programme - I suspect it may need to be adjusted, and what was the diameter of your original piece of glass?
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jackiesimmonds
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« Reply #4 on: February 12, 2015, 04:55:45 PM »

It is a small bowl, only about 6" diameter now, tho the flat fused piece was wider.  I used the Bullseye slump prog. which is set into my programmer for my Hobbyfuser.

1. Rate 167 - 640 10mins
2.        Full - 482  1 hr
3.         56  -371  00.01
end.

I need to check this against the suggestion on the moulds website, but that is in F not C and I cannot do it in my head.

As I look at it closely now, it is even less successful than I thought, it is not only thick, but has slumped unevenly! Maybe because I fused a patterned top layer to a base layer...the base is clear, the top layer has a mix of streaky and irridescent glass. 

Also, on the "high" side of the bowl, I can feel a very slight difference in the smoothness of the glass....I suspect that the mould has not been evenly made, I am sure this doesn't help!  The whole thing is a disaster ...and looks VERY unprofessional, which I really dislike.  Looks like a child made it.

Well, I am quite glad that the mould cost me nothing, although I am sure that the maker will want to see me make a successful bowl with it........oh dear.
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Zeldazog
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« Reply #5 on: February 12, 2015, 06:42:48 PM »


I need to check this against the suggestion on the moulds website, but that is in F not C and I cannot do it in my head.


I like this site, because although temperature conversion is easy to find, rate conversion is less so, so this is bookmarked on computer and on phone :-)

http://www.warmglass.com/phpBB/index.php

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Pat from Canvey
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« Reply #6 on: February 13, 2015, 02:55:10 AM »

I looked at the site and was surprised to find they were disparaging using terracotta pots for pot melts. I've always used them and frequently drilled extra holes with no problems. I just throw the pot away after use because they're so cheap. Oh well I suppose they want you to buy their more expensive molds  Roll Eyes  Roll Eyes  Roll Eyes  Roll Eyes  Roll Eyes I also use terracotta flower pots in the vitrigraph kiln, 0.69 in the local garcen centre.
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flame n fuse
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« Reply #7 on: February 13, 2015, 11:24:56 AM »

The programme we have used for successful slumps of 20 cm diameter bowl in hobbyfuser is this
rate 100 to 550C soak 15 min
rate 166 to 638 soak 10 min
rate full to 515C soak 60 min
rate 50 to 300C soak 0 min
rate full to 21C switch off

uneven slumps could be due to several things for instance, having one side of the mould close to an edge of the kiln, or on a high shelf rather close to the elements
or having glass of rather variable thickness - how even was your top layer?
or having one side of the glass 'drag' on the mould during the slump - due to uneven kiln wash for instance.

When you talk about difference in the smoothness - do you mean devitrification, or are you getting jaggy points?

I know this is more complicated than your programme (which is the same as one on the bullseye website for a 12 inch diameter piece.), but we find it works well and so we stick with it.

It sounds a bit as if it got too hot and has started to flow, not just slump. This document is well worth a read .....

http://www.bullseyeglass.com/images/stories/bullseye/PDF/TechNotes/TechNote_4_2015.pdf
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jackiesimmonds
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« Reply #8 on: February 13, 2015, 12:21:26 PM »

wow, thanks for this schedule - I am nervous of changing my programmes because the kiln is new and I am a bit scared of the programmer!    But I will have a go.  I need to, because I want to do some fire polishing and there isn't a programme for that.  I have to bite the bullet.  It is just SO different to my little paragon kiln's programmer.  that drives me nuts, it is a 12 button programmer and I hate it.  It has taken me a year to become comfortable with it.   (It is my enamelling kiln).

As for the glass - the top layer was a mix of streaky, and iridised glass. Cut, curved pieces.    I did my best with cutting it, sweated a lot and the shapes were actually quite good!  And in between the curved "stripes", in the centre of the bowl, I used frit and pieces of both glass, for interest.  I will try the mould again, with a simple two circle fused piece, and see what happens.

Pat, I am sure Bonny Doon want people to buy their moulds!   they are in business and want to survive.  they won't survive from people like me, who pinch their idea and try to copy it......perhaps this is why my bowl failed...poetic justice.......
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marklaird
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« Reply #9 on: February 13, 2015, 12:41:48 PM »

Hi Jackie,
Just read your thread - did you fuse the glass before you slumped it, or did you try to do it all in one go?
I make shallow bowls all the time using a normal slump mould but always full fuse my glass first and then slump in a second firing.
Mark
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jackiesimmonds
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« Reply #10 on: February 14, 2015, 03:12:55 AM »

Mark, I definitely DO fuse first, slump after...takes me two nights of having the kiln on and a lot of frustration that I have to wait...but I do it right!

Actually, I just read a post on another site, a tutorial about irid glass.  It said that Irid glass does not stretch.  Perhaps, since my little bowl has two curving strips of Irid in with streaky glass, and one strip is quite wide , perhaps THAT was part of the problem for the uneven slumping.   Doesn't totally explain the thickening, but might answer some of my difficulty with this wee bowl.
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Pat from Canvey
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« Reply #11 on: February 14, 2015, 04:58:04 AM »

Pat, I am sure Bonny Doon want people to buy their moulds!   they are in business and want to survive.  they won't survive from people like me, who pinch their idea and try to copy it......perhaps this is why my bowl failed...poetic justice.......
True but I find it distasteful that they are spreading untrue information.
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flame n fuse
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« Reply #12 on: February 14, 2015, 05:48:23 AM »

Hi Jackie
This is worth a read too   http://www.bullseyeglass.com/images/stories/bullseye/PDF/other_technical/slumping_mold_tips.pdf
 and perhaps the tips for cone shaped moulds on this page are also relevant    http://www.bullseyeglass.com/methods-ideas/index-of-articles.html
I have an enormous bowl with large pieces of irid and it is beautifully fused and slumped. It'll be a matter of getting the programme right.
HTH
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jackiesimmonds
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« Reply #13 on: February 14, 2015, 12:15:40 PM »

I agree Pat.

And thanks for the tips, HTH, I will study those.  I am sure you are right about not having the programme right.

I had such a frustrating day with glass....I have made lots of pieces at my college, out of Float glass - fused, then slumped.  This time the piece I made, float with inclusions, slumped over a former, came back with BLACK edges, and was totally devitrified.  Looks ghastly. My tutor said I should have put Borax on it...but I wasnt told to do that with any of my other pieces, which slumped fine and did not devit.  I do not understand.  I dont do the firings, mind you, those are done by the college so I have no idea what programmes are used.  Such a waste of my time and glass, the vase is horrid-looking.  So much to learn, so little time.....
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