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Plaster mold

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osnat
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Plaster mold

Postby osnat » Sat Mar 15, 2014 1:14 pm

Hello everyone,
I made my mold from Plaster and
Quartz.
I looked You Tube video about Pate de Vere artist Kmiyaki Higuci .
http://m.youtube.com/watch?v=ivTt2Uc6zew
i saw their when the artist brook the mold , the glass was very clean from the mold matrial.
I tried firing 1500 f and also 1310 f and is stick.
Do you know which materials are mixed to creat the mold?

All the best
Osnat

Jenna
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Re: Plaster mold

Postby Jenna » Sun Mar 16, 2014 10:29 am

I watched the video and indeed there doesn't appear to be any kiln wash on the mold (no coloring). I have no idea how they get such a beautiful finish on the glass without. Can't wait to hear from the forum about this.

I have tried many different plasters/ refractory mixes and have yet to find one that does not stick to the glass without some type of separator. Most of my pieces are small, open face molds with very fine detail. I use R&R 101 for my molds and Hotline primo as my separator. The glass comes out of the mold without any sticking (usually). I fire to 1470 deg.

Heres what works for me...I pour the kiln wash into my molds, swirl it around a little then pour it back out. The kiln wash is in the mold for about 10 seconds. This is much quicker that brushing it on and leaves a very smooth surface without any brush marks and doesn't obscure any of the detail. I usually get two firings out of each mold and just lightly brush out the old kiln wash and pour some new wash right on top.

Hope this helps some although it is not exactly the answer you're probably hoping for.
Cheers,
Jen

Morganica
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Re: Plaster mold

Postby Morganica » Sun Mar 16, 2014 4:49 pm

The Higuchis use a special mix that's available (in the US, at least) through Corning. My understanding is that it's typically used in Japan for low-temp metals casting. I've talked to the Corning order desk about it a couple of times (it's not on their store site, you have to call) but as I recall it was some horribly expensive price, i.e., $150 for a bag plus shipping, so I've never actually purchased it.

Overall, plaster molds shouldn't require a release; that's one of the reasons you use plaster-silica in the first place. However, like Jen, I do use kilnwash with some commercial mold mixes (R&R 910, for example), and I use the same technique: Mix up a thinnish kilnwash, pour it into an uncured mold--I like to fill mine all the way to the top, then immediately pour it out. If the mold has already cured and dried, I find that too much kilnwash will get sucked onto the mold and lose detail, so the mold should be dampish. It'll give a satiny finish to the glass and release completely.

I use two or more different mixes when I make my own refractory. The surface mix, the one touching the model, is usually a combination of alumina and dental stone, such as Garreco Tecstone or USG Ultrastone. I've found (and I think a couple of moldmaking books also talk about this), that silica next to the glass can exacerbate sticking, even though the silica has a much higher melting temperature. And--at least in pate de verre, where you've got moisture and abrasive glass particles being pressed into the mold--#1 pottery plaster tends to bleed a bit into the surface frit and produce scum, so that the glass has a greater tendency to stick to the mold. So I eliminate both from any part of the mold that touches glass.

I've also found that the thinner the mold, the less tendency there is to stick to the glass. Or so it seems--I haven't actually figured out why yet.
Cynthia Morgan
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osnat
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Re: Plaster mold

Postby osnat » Mon Mar 17, 2014 2:38 am

Thanks .

S.TImmerman
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Re: Plaster mold

Postby S.TImmerman » Sat Apr 19, 2014 4:29 am

I dont mean to hijack this but is all hydroperm the same? I bought some recently and 5 pounds was 14.00 and i just noticed sheffield pottery has "hydroperm " 50 lbs for 29.00. I ended up buying 10 lbs for 28.00.

http://www.sheffield-pottery.com/U-S-Gy ... drop50.htm

Thank you!

Shereen

Morganica
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Re: Plaster mold

Postby Morganica » Sun Apr 20, 2014 12:00 am

Hydroperm is trademarked, so if something is labeled "Hydroperm" it's either violating that trademark or it's the same USG plaster. Does yours bubble a bit, and make a very hard, aerated plaster? It's most likely the same Hydroperm.

I generally pay a bit more than $29 for the 50-lb sack, but $14 for a 5-lb box? You mean $140 per BAG?

Wow.

Like most gypsum plasters, Hydroperm has a limited shelf life at its peak performance so if you only used a tiny amount in a year I suppose buying it by the 5lb box would be appropriate. But you'd be much better off going in on a 50-lb bag with a few friends for THAT price. Whoa.
Cynthia Morgan
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S.TImmerman
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Joined: Wed Nov 25, 2009 9:23 am
Location: San Diego ,Ca

Re: Plaster mold

Postby S.TImmerman » Mon Apr 21, 2014 1:52 am

Im kicking myself i didn't shop around like i usually do. I ended up doubling my order too.
https://www.fusionheadquarters.com/Sear ... =Hydroperm

nbobb
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Re: Plaster mold

Postby nbobb » Thu Apr 24, 2014 6:12 pm

Fenton and Kerwin's book, Pate de Verre and Kiln Casting of Glass, gives a lot of information about different kinds of investment mixes. One of their mixes has kaolin clay (or EPK) included, which acts as a property modifier and, according to them, helps the mold seperate from the glass. Their proportions are: 4 parts plaster, 4 parts silica and 1 part EPK. This proportion of EPK is quite a bit higher than the amount we used in Alicia Lomne's pate de verre class - I believe she added 1 cup per 10 pound plaster/silica mix. I used that mixture in class and at home and it stuck horribly. But, the pate de verre process of compacting the frit against the mold may have also added to the sticky-ness, I'm not sure.

I recently did some casting and used the higher proportion of EPK from the book but I was chicken and also used a little kiln wash too. My mold hardly stuck at all. But, that being said, I ran it up to 1525 F for 4 hours, much higher than a pate de verre firing. At higher temps this mold mix becomes somewhat soft so that may have been the reason it was so easy to remove. I believe the Higuchis cast around 1600 F in their firings and that may be another reason the mold seperated easily from the glass. The plaster investment that they use can keep its strength at such high temperatures better than the formulation I was using, but I've got what I've got and it worked fairly well for what I was doing.

Your mileage may vary, of course, and will probably depend on what you're doing and how high you're firing.
Nancy Bobb
Firewalker Studio
http://www.firewalkerstudio.com

Morganica
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Re: Plaster mold

Postby Morganica » Thu Apr 24, 2014 7:39 pm

nbobb wrote:Fenton and Kerwin's book, Pate de Verre and Kiln Casting of Glass, gives a lot of information about different kinds of investment mixes. One of their mixes has kaolin clay (or EPK) included, which acts as a property modifier and, according to them, helps the mold seperate from the glass. Their proportions are: 4 parts plaster, 4 parts silica and 1 part EPK. This proportion of EPK is quite a bit higher than the amount we used in Alicia Lomne's pate de verre class - I believe she added 1 cup per 10 pound plaster/silica mix. I used that mixture in class and at home and it stuck horribly. But, the pate de verre process of compacting the frit against the mold may have also added to the sticky-ness, I'm not sure.

I recently did some casting and used the higher proportion of EPK from the book but I was chicken and also used a little kiln wash too. My mold hardly stuck at all. But, that being said, I ran it up to 1525 F for 4 hours, much higher than a pate de verre firing. At higher temps this mold mix becomes somewhat soft so that may have been the reason it was so easy to remove. I believe the Higuchis cast around 1600 F in their firings and that may be another reason the mold seperated easily from the glass. The plaster investment that they use can keep its strength at such high temperatures better than the formulation I was using, but I've got what I've got and it worked fairly well for what I was doing.

Your mileage may vary, of course, and will probably depend on what you're doing and how high you're firing.

The Higuchis don't have pottery plaster in their mix, which has something to do with it. Actually the higher the temps with standard plaster/silica, the more likely it will stick; it's another good reason to keep your temps down if you can. And you're right, the action of pushing abrasive little particles of glass up against damp refractory doesn't help the situation at all. Unlike billet (or dripped-in glass), the frit pack is right on top of the slightly dissolving refractory so the runoff gets in between the particles and kinda blurs the interface. It not only exacerbates sticking, it also contaminates the glass and increases the chances for hazing and devit. (And, with all the surface area it exposes, frit is far more likely to devit anyway).

EPK gives you a little better detail than standard plaster/silica, and it also makes release a little easier. I've tried a number of refractory formulations, though, from talc to dental stone. So far the best facecoat combinations I've used substitute alumina for silica flour, and use about 10% EPK. Then I toss in a couple handsful of a good kilnwash while I'm at it. Since doing that I get no sticking at all with pate de verre castings.

HOWEVER...I still get some scum, probably from the packing action. I'm not sure if it's truly devit, or simply haze created by embedding plaster residue in glass. Doesn't bother me much because all my pate de verre pieces are extensively coldworked anyway. But if I ever get back into test mode I'll see if I can resolve the scum with dental stone.
Cynthia Morgan
Marketeer, Webbist, Glassist
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"I wrote, therefore I was." (me)

Geo
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Re: Plaster mold

Postby Geo » Fri Apr 25, 2014 10:57 am

Cynthia, do you happen to know what is in the Higuchi's mix instead of pottery plaster?

I hope you report back with your experiments. For me, with pate de verre specifically, my main focus right now is properly packing my molds. Some of those molds include fine details on walls which are quite vertical. Is there something about the wettish plaster in pdv molds having contact with the glass that contributes to successfully packing the mold? I always assume that cold working will be involved.

Morganica
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Re: Plaster mold

Postby Morganica » Fri Apr 25, 2014 9:13 pm

Well, Richard Whiteley once said something about the piece you take out of the kiln being only half-finished, and coldworking takes you the rest of the way (or words to that effect) and I think that's almost a given with casting. There are times (almost always smaller billet-cast pieces) when I can break the piece out of the mold and I'm done...but that's pretty rare. And (for me, anyway) the post-firing grinding, shaping, and polishing are as much a part of sculpting as making the original model or tooling the wax.

I don't know which plaster/cement is used in the Higuchi mix. I've been told by Higuchi students that it's an industrial refractory intended for casting aluminum car components. If you Google around, you can find companies that make such refractories for aluminum foundries and some of them share their formulations.

Glass powder (especially) will stick to damp plaster beautifully--the problem is what you do when the water's driven out of the mold and there's nothing left to hold the the particles against the refractory. The stickiness of the plaster is only important in the actual packing process. The trick is to use varying particle sizes with a binder so that the pieces lock together, then hopefully they stabilize against the bottom and stop moving. If that doesn't work, it's inert filler time!
Cynthia Morgan
Marketeer, Webbist, Glassist
http://www.morganica.com/bloggery
http://www.cynthiamorgan.com

"I wrote, therefore I was." (me)

S.TImmerman
Posts: 235
Joined: Wed Nov 25, 2009 9:23 am
Location: San Diego ,Ca

Re: Plaster mold

Postby S.TImmerman » Wed Feb 04, 2015 4:20 am

I found a place that does aluminum casting and sells the investment. I have contacted them to buy some. I'll let you know!

http://www.avalon-castings.com/investme ... g/aluminum


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