how to create a flat bottom on the slump with a ball mould?

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how to create a flat bottom on the slump with a ball mould?

Postby Babette (Shawn) » Tue Aug 07, 2012 6:02 am

I am using Bullseye's largest round ball mould, it is 22" in diameter. I have heard there is a way to set fiber paper or fiber board inside the round mould so when the glass slumps the bottom of the bowl flattens eliminating rock & roll? Has anyone done this, and if so how is it best done? Do I need to put a stiffener on the fiber paper? How thick a fiber paper works best? Can I create an actual foot (raised ridge) Any suggestions are much appreciated. THANK YOU!
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Re: how to create a flat bottom on the slump with a ball mou

Postby Dairy Queen » Tue Aug 07, 2012 9:34 am

I'd mix up a very thin, self leveling plaster mold mix. Pour to depth desired. Probably need no more than 1/2 cup. I have and love that mold. Balance is forced upon your piece by this mold. But I can understand your love of the shape, and need for stability.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Bert Weiss » Tue Aug 07, 2012 9:49 am

You will have to get creative. Remember that the mold doesn't have to be perfect, the glass won't fall in to small anomalies, on the edge of the flat spot. You could use fiber paper supported with powder (like dry kilnwash, sand, or a mixture of refractories. Or a piece of 1/4" fiber board, or that ceiling tile stuff, Brad sells.

I'm not practiced in slumping the soft fusing glasses, so I don't know how hard it would be to make some feet happen with dimples in a mold. You would have to get hot enough to get the glass to go in to the dimples, but not be so hot that the bowl falls in to a puddle.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Morganica » Tue Aug 07, 2012 10:35 am

Sift some dry kiln wash into the mold, level it out and tamp it down. Dry plaster of Paris works, too. The glass will slump down onto it. The powder will be more forgiving (and a lot less mess) than a poured mold mix.

You can also cut fiber paper rounds to fit, put them in the bottom of the bowl and then dust with dry kiln wash or plaster to level and smooth it out.

On the feet, yes, absolutely but it can be tricky. I like to prefuse the base/feet in the mold while I'm firing the blank. Then I coldwork both, put the base back in the mold with fiber paper cutouts to keep its shape, set the blank on top and do a cool tack fuse with a very long anneal. The blank will come down on the base and stick, giving you a bowl with feet.

This is a tack fuse and prone to stress--experiment with doing the shape you want in clear first and check it for stress before you do the real thing; some designs will take a lot longer than others. I wrote about an experiment in this a few years back:
http://www.morganica.com/bloggery/2007/glasswork/fusingtack-fusing/bad-glass-day/
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Re: how to create a flat bottom on the slump with a ball mou

Postby Bert Weiss » Tue Aug 07, 2012 11:32 am

Morganica wrote:Sift some dry kiln wash into the mold, level it out and tamp it down. Dry plaster of Paris works, too. The glass will slump down onto it. The powder will be more forgiving (and a lot less mess) than a poured mold mix.

You can also cut fiber paper rounds to fit, put them in the bottom of the bowl and then dust with dry kiln wash or plaster to level and smooth it out.

On the feet, yes, absolutely but it can be tricky. I like to prefuse the base/feet in the mold while I'm firing the blank. Then I coldwork both, put the base back in the mold with fiber paper cutouts to keep its shape, set the blank on top and do a cool tack fuse with a very long anneal. The blank will come down on the base and stick, giving you a bowl with feet.

This is a tack fuse and prone to stress--experiment with doing the shape you want in clear first and check it for stress before you do the real thing; some designs will take a lot longer than others. I wrote about an experiment in this a few years back:
http://www.morganica.com/bloggery/2007/glasswork/fusingtack-fusing/bad-glass-day/
Question, Cynthia. Given that any 3 low points will create stability, wouldn't it be more effective to fire to a tack fuse temperature, but just create the dimples, and not worry about annealing a tack fuse? The shape would have to be such that the dimples exceeded the depth of the bottom of the sphere. I've never tried this, but I think I will.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Morganica » Tue Aug 07, 2012 12:01 pm

Bert Weiss wrote:Question, Cynthia. Given that any 3 low points will create stability, wouldn't it be more effective to fire to a tack fuse temperature, but just create the dimples, and not worry about annealing a tack fuse? The shape would have to be such that the dimples exceeded the depth of the bottom of the sphere. I've never tried this, but I think I will.

Sure, as long as there is enough glass to make both base and feet (otherwise the inside of your bowl will also have dimples), and you have perfectly level dimples. To do that I'd just cut holes in fiber paper. The issue will be making sure the dimples slump all the way to the mold so the bowl doesn't wobble but the bowl sides don't sag. You wouldn't want to do a lot of grinding on those feet.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Dairy Queen » Tue Aug 07, 2012 1:23 pm

Dry plaster cannot be used in that ball surface mold with out leaving some sort of marks on the bowl. The slumping glass will pick up the texture of the powder by pressing and leaving a small lump in the bowl's bottom, at the touchdown spot.

Very wet plaster poured into the bottom of that mold will self level with a little shimmy, shimmy (mold to big and heavy to tap for tamp). The wetter the mix, the easier it levels, and the smoother the surface when dry.

If you need your bowl shim to be removable, use vaseline or mold soap on mold before pouring in very wet plaster. Either will fire out of the mold.

Good luck.

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Re: how to create a flat bottom on the slump with a ball mou

Postby Dairy Queen » Tue Aug 07, 2012 1:26 pm

CORRECTION:

The slumping glass will pick up the texture of the powder, AND it will leave a small lump outward in the bowl's bottom at the touchdown spot.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Morganica » Tue Aug 07, 2012 1:58 pm

Dairy Queen wrote:Dry plaster cannot be used in that ball surface mold with out leaving some sort of marks on the bowl. The slumping glass will pick up the texture of the powder by pressing and leaving a small lump in the bowl's bottom, at the touchdown spot.

Very wet plaster poured into the bottom of that mold will self level with a little shimmy, shimmy (mold to big and heavy to tap for tamp). The wetter the mix, the easier it levels, and the smoother the surface when dry.

If you need your bowl shim to be removable, use vaseline or mold soap on mold before pouring in very wet plaster. Either will fire out of the mold.

Good luck.

Rose

Have you actually tried any of this? First, dry kilnwash or plaster of paris has less texture than applied kilnwash, especially when sifted in and tamped down. Unless you've really screwed up the surface, it won't leave a mark. You can also do this with talc--any fine powder. It's my preferred method for altering the base of a slumping mold. I've done perhaps 60 of these in various sizes, probably 10 or 12 with the largest size ball mold that Bullseye sells. None have "marks." Nor do they have "small lump outward in the bowl's bottom at the touchdown spot," whatever that means.

Second, the more water you add to plaster, the weaker it gets, and the more prone it is to cracking, especially if it's dried rapidly. Really wet plaster of paris in a slump firing may resemble a dried lake bed by the time it gets to process temps, not exactly a great slumping surface.

Third, most of the plasters out there are automatically "removable" after firing, because they degrade at processing temps and crumble apart--they'll be even easier to remove if the mold had kilnwash on it to begin with. Vaseline is problematic in a glass mold, since it tends to leave a black-brown sludge when it burns out. Mold soap will be gone with the steamout. Neither will facilitate removing fired plaster.
Last edited by Morganica on Wed Aug 08, 2012 10:24 am, edited 1 time in total.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Jeff Wright » Tue Aug 07, 2012 2:04 pm

And now for something completely different...

I have a smaller version of this mold (mould for the rest of the English speaking world). Rather than deal with it in the mold, I do a very simple coldworking exercise after the slumping. A small amount of 80-100 grit and a few drops of water on a flat glass plate make a great grinder and it takes about 2 minutes to grind a very small flat exactly where I want it. I usually want to do some touch ups on the rim anyway. This way I get the piece to sit exactly where I want it. I've even ground off-center just for effect.

Your mileage may vary.
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Re: how to create a flat bottom on the slump with a ball mou

Postby The Hobbyist » Tue Aug 07, 2012 2:32 pm

I have flattened the bottom of rocking bowls by putting the bowl on the shelf and bringing it to slump temp. As the temp rises and nears the target temp I open the kiln a little and see if the bowl will still rock. As soon as it is stable I crash cool and proceed to the anneal cycle. The bowl does not deform because all its weight is centered on the bottom spot so it will move first. The key is peeking, testing and stopping the slump before it can get out of control.

Jim
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Re: how to create a flat bottom on the slump with a ball mou

Postby Bert Weiss » Tue Aug 07, 2012 2:50 pm

One of my signature pieces, is a rectangular platter, that has dimples. It is true that these leave a dent on the other side. These dents don't bother me. I wouldn't consider grinding the dimples. The theory is that any 3 points will create stability. So, yes it depends on your aesthetic. Certain stuff really doesn't bother me, while other things do. I don't care for texture that looks like it shouldn't be there. My solution is not to try and make it disappear, but to create texture that is intentional, and improves the look.

Jim, I like your solution, but for anybody trying to earn a living, an extra firing is not part of the design picture. If efficiency and time are not particular concerns, you have an interesting plan.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Babette (Shawn) » Tue Aug 07, 2012 2:54 pm

Thanks Jeff but this blank has quite a bit of design on the back side, done with powders and I hate to grind any of that off. Also because this bowl will be pretty large wouldn't I have to create a large flat area to get it to sit well?

Regarding mold vs mould...I just got back from a road trip to BC Canada and I have new respect and some across-the-border envy...the Canadians are so relaxed and polite! I was up in the islands off of Victoria and it was...heaven! So I came back saying "cheers" and an occasional "aye?" And I just had to spell mold as mould. I'll get over it soon enough aye? :wink:

PS Northern California is burning again, we have an out of control 15,000 acre fire just a few miles away. Our home is safe from flames right now but I may start wearing my respirator.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Stephen Richard » Wed Aug 08, 2012 4:36 am

Babette (Shawn) wrote:.......
Regarding mold vs mould...I just got back from a road trip to BC Canada and I have new respect and some across-the-border envy...the Canadians are so relaxed and polite! I was up in the islands off of Victoria and it was...heaven! So I came back saying "cheers" and an occasional "aye?" And I just had to spell mold as mould. I'll get over it soon enough aye? :wink:

.......


Och aye th noo (translation: oh yes, soon)
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Re: how to create a flat bottom on the slump with a ball mou

Postby Morganica » Wed Aug 08, 2012 10:31 am

The other thing you can do, btw, is leave your bowl intact but put it on a ring stand. It doesn't have to be big--I've used a one-inch glass ring on the big honkin ball molds. Just set it on the table and put your bowl on top, or glue it on. You can also grind a flat place on three store-bought marbles and glue them on as feet.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Valerie Adams » Wed Aug 08, 2012 12:22 pm

This is just one reason why I love WG so much!

I've never even used my ball mold but I know when I do, I'm armed with all sorts of great to-dos and not-to-dos!
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Re: how to create a flat bottom on the slump with a ball mou

Postby Jeff Wright » Wed Aug 08, 2012 6:33 pm

Another option - and one I use for my glass marbles, ordinary O-rings that you get at the hardware or automotive store. I use half-inch black or clear rings to keep large 3+ inch diameter marbles from rolling around. I was at an art fair a week or so ago, and everyone was amazed and that solution. I'm positive it's not original with me, but like many things I "discovered" it on my own. I haven't tried it, but larger automotive O-rings in the 2-3 inch range should work if you don't want to cold work the bottom or put some appendage onto the piece.

The small size ones give a nice shadow line and lift the marble slightly off the shelf to give an impression that its floating. I choose the color depending on the marble and it's coloration.

They tend to slightly "stick" to the glass which I find is actually a good thing. There isn't a mark left and a slight nudge moves removes them from the glass. This keeps them in place if someone bumps the shelf or table accidentally.
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Re: how to create a flat bottom on the slump with a ball mou

Postby Morganica » Thu Aug 09, 2012 1:47 pm

Bert Weiss wrote:One of my signature pieces, is a rectangular platter, that has dimples. It is true that these leave a dent on the other side. These dents don't bother me. I wouldn't consider grinding the dimples. The theory is that any 3 points will create stability. So, yes it depends on your aesthetic. Certain stuff really doesn't bother me, while other things do. I don't care for texture that looks like it shouldn't be there. My solution is not to try and make it disappear, but to create texture that is intentional, and improves the look.

Jim, I like your solution, but for anybody trying to earn a living, an extra firing is not part of the design picture. If efficiency and time are not particular concerns, you have an interesting plan.

I think it just depends on the end goal--sometimes an extra firing is more efficient than any other method, sometimes it's more efficient to coldwork. I have done projects where I wanted the bottom shapes to telegraph to the inside of the vessel, others where I want sometime entirely different going on.

I think creating a texture to disguise potential issues is one good way to solve the problem. Another is to just control the slump firing very closely so the glass never picks up the unwanted texture in the first place. I learned that from somebody on this board (don't remember who) a long time ago, and it really jumpstarted my ability to modify a commercial mold. (so thanks to whoever)
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Re: how to create a flat bottom on the slump with a ball mou

Postby Thomas Decker » Thu Aug 09, 2012 5:40 pm

I have the same mold I solved the problem by putting the bowl on a 6" bonsi stand . ( you can find tham on line )it gets the bowll up so light can go through the bowl , protects the glass and the table and gives it some nice feet. and I lreally like the combination of the wood and the glass.
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Re: how to create a flat bottom on the slump with a ball mou

Postby seachange » Fri Aug 10, 2012 10:37 pm

Thomas Decker wrote:I have the same mold I solved the problem by putting the bowl on a 6" bonsi stand . ( you can find tham on line )it gets the bowll up so light can go through the bowl , protects the glass and the table and gives it some nice feet. and I lreally like the combination of the wood and the glass.


Hi Thomas

just made a google and lycos search for bonsai stands, but only found flat timber disks...is this what you use?

Many thanks, seachange
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