Borax spray on plaster molds - WarmGlass.com

Borax spray on plaster molds

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Jenna
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Borax spray on plaster molds

Postby Jenna » Wed Jun 06, 2012 10:40 am

I am about to load up another round of molds with frit and am hoping to use a borax spray to prevent any devit. Some of the spray will undoubtedly end up on the plaster (R and R 101). Will this degrade the plaster in any way or have some kind of reaction?
Also, everyone describes devit as "white, scummy, cloudy" however the 'devit' or whatever it is that I'm trying to prevent that has showed up on my recent pieces is more like a oily sheen, sort of like gasoline in a puddle. Is this devit or something else?

Valerie Adams
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Re: Borax spray on plaster molds

Postby Valerie Adams » Wed Jun 06, 2012 12:36 pm

What kind of glass are you using? Bullseye's Marzipan for instance will often self-iridize. If you're using float or tempered, could it be the tin side showing?

Jenna
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Re: Borax spray on plaster molds

Postby Jenna » Wed Jun 06, 2012 2:18 pm

I'm using Uruboros 96 coarse and medium frit. All transparent. I use it straight out of the container without washing or rinsing it and am not looking to add this step to my process unless a bunch of you swear by it. I do realize the importance of clean glass however, and have thought that maybe its coming from my fingertips when I pack the glass. I don't wear gloves.

The sheen i described feels very smooth, sometimes has a mottled pattern, sometimes only covers half of a piece (my pieces are on the small side 2"-8") and seems to be mostly on the darker colours. It doesn't effect the clarity of the glass, it can only be seen when there isnt light coming through the glass, but I would like very much to cast my pieces without this. Cold work or fire polishing are not options.

Does anyone have any pictures of classic, textbook devit they can post?

Valerie Adams
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Re: Borax spray on plaster molds

Postby Valerie Adams » Wed Jun 06, 2012 2:51 pm

I can't comment on Uro glass, sorry.

Here's a photo I found doing a Google search for divitrification:
Devitrified_surfaces_bottlesW1.jpg

rosanna gusler
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Re: Borax spray on plaster molds

Postby rosanna gusler » Wed Jun 06, 2012 4:49 pm

borax will cause mondo sticking of the glass to whatever the borax touches. rosanna
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Bert Weiss
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Re: Borax spray on plaster molds

Postby Bert Weiss » Wed Jun 06, 2012 5:22 pm

rosanna gusler wrote:borax will cause mondo sticking of the glass to whatever the borax touches. rosanna
this is my experience, although I never used it with investment molds. It does stick to kilnwash and fiber board.

I suggest you try rinsing your frit. Get a fine enough strainer, rinse away the fines, then put it in a clean bowl in a 350 oven until dry. See if that stops your scumming. Fines are not pretty.
Bert

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Morganica
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Re: Borax spray on plaster molds

Postby Morganica » Wed Jun 06, 2012 5:55 pm

So...Where is this occurring? On the side against the mold? On the top (away from the mold?) On the edges? What kind of schedule are you using and, in particular, how are you drying your mold? In my experience with casting soda-lime into a mold, the worst scum/devit occurs with opal powders wet-packed into a still-moist plaster (50/50 plaster/silica). I get the cleanest, clearest results with pieces made from a single billet, dripped into a pre-fired mold containing little or no silica flour.

Very slight devit can look sorta like your description, i.e., a satiny sheen on shinier glass, but as Val pointed out it could be a characteristic of the type of glass you're using, too. Rinsing frit to remove fines isn't a bad idea, but I don't think it really does much for your problem, and it takes longer, tends to lose some glass along the way and might make things worse, if the problem is related to water in the filled mold and the frit isn't all the way dried before using.

A wet refractory mold outgasses all kinds of crud when the water evaporates during firing, and that stuff deposits on the glass, particularly the glass inside the mold and on the edges. I can reduce that significantly simply by pre-drying the mold in the kiln, removing at least the mechanically held water before firing. That means putting the mold into a vented kiln without glass, heating it to between 240F and 300F, and keeping it there until about an hour after you're not getting any water vapor from the kiln. (A mirror held up to the vent doesn't fog). Turn off the kiln, let it come back to temp, and then fill and fire. (It takes longer than you think. )

I've never tried a borax spray on a mold, mostly because there's already such a chemical soup in the mold and I don't like to add to it. I'd agree with Rosanna that borax might make it harder to remove the refractory from the glass. What can help is a very light application of a good kilnwash. I make it slightly runnier than usual, pour it into the mold, wait about 30 seconds, then pour it out. Then I run through the drying cycle..
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Jenna
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Re: Borax spray on plaster molds

Postby Jenna » Wed Jun 06, 2012 11:07 pm

I do dry my molds thoroughly before loading them with glass. Luckily they are one the small side and dry fairly quickly: 3-7 days on a drying rack, on top ( outside) of the kiln during a firing, and then in the kiln for 2 hours at 290 deg. This is all before the first shard of glass comes anywhere close them. They are no longer cool to the touch and are 'featherweight' by the time I load them with glass. I also refire most of my molds a second or third firing so I'm thinking all the moisture and gunk is well out by then. Of course, sitting around the studio, waiting for the next firing, they can re-absorb some ambient moisture but unless it's really soggy and wet for days ( like the past few weeks here in vermont) I don't consider this a major consideration. Also for anyone using MR-97 as a release: this stuff works great but really doesn't like moisture so if you need another reason to thoroughly dry your molds, keep this in mind.

The sheen/ devit is mostly away from the mold surfaces. It is very subtle and hard to photograph as you can only see it in certain light. I will post a picture tomorrow (camera not compatible with my beloved iPad) once I fire up the old laptop. I will also post my most recent firing schedule.

Thanks for all the replies.

Jenna
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Re: Borax spray on plaster molds

Postby Jenna » Fri Jun 08, 2012 9:59 am

Here is a picture of what I have been trying to describe. The clear glass around the blue is only a background I used for the photo and is not part of the piece. So is this Devit or something else?
Attachments
DSC03980.JPG
devit or something else

Joe Pfeifer
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Re: Borax spray on plaster molds

Postby Joe Pfeifer » Thu Jun 28, 2012 5:29 pm

Here are some views of devitrification (same piece). What you are seeing is actual crystals beginning to grow. I suppose under the right temperature conditions, and enough time, you would start seeing actual crystals. You can see in the photos some large patches which are the molecules starting to line up and select growth planes. If you had a plate full of bb's you would see patchy patterns as they bb's find resting places. Hope this helps.
Attachments
DSCN0250.JPG
DSCN0249.JPG
DSCN0248.JPG

Morganica
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Re: Borax spray on plaster molds

Postby Morganica » Thu Jun 28, 2012 7:32 pm

Nice shots. And yup; I've had them go all the way to crystals. Looks like whiskery rock candy--had that happen with pate de verre in a plaster/silica mold once and I was surprised at how large (maybe 3-4 mm) the crystals can actually become.
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Peter Angel
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Re: Borax spray on plaster molds

Postby Peter Angel » Thu Jun 28, 2012 7:41 pm

I used to get much devitrification using R&R 101. Always on the top (air) side of the glass.

I then switched to a 1:1 plaster:silica with a scoop of R&R 910 thrown in as a reinforcement to prevent cracking and I've had neither cracks nor devit ever again.
Peter Angel
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