challenges making a glass mask - WarmGlass.com

challenges making a glass mask

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roykirk
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challenges making a glass mask

Postby roykirk » Wed Jul 01, 2015 3:21 pm

Hi All - I've been chewing up days upon days of kiln time trying to make a glass mask and I'm just not quite getting it right. I was hoping for some advice that might save me some time.

What I did was make a 3D scan of my wife's face, printed it out on my 3D printer, then used the mask to make a concave clay impression that was then fired. So what I'm trying to do is get the glass "inside" the face sort of akin to slumping. I'm using a Kingpin 88 kiln and simply using their pre-programmed settings (sorry, I don't have the breakdown of all the program settings at hand right now). I first tried to get a flat piece of glass in to the face mold using the slumping program. This worked reasonably well, but I couldn't get the face to fill in completely despite multiple attempts and manual tweaking of temperatures. I could just never get the glass to slump fully in to the nose. When I tried to use the casting program, all the glass simply melted in to the front of the face and I lost all the other features. The next thing I tried was filling the inside of the face with crushed glass frit and then running the casting program again. This resulted in a nicely filled mold, but the glass cracked in several different places upon cooling (using tested 90 COE glass). This happened several different times trying the frit method.

If anyone has any ideas or recommendations that will save me some trial and error time, I'd appreciate it.

Bert Weiss
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Re: challenges making a glass mask

Postby Bert Weiss » Wed Jul 01, 2015 3:29 pm

Mold material, glass, and shape must all be compatible for a casting to come out intact. Generally, glass shrinks more than ceramic, so I thought you would be OK. Perhaps the shape of the mold is such that it gets in the way of the glass's contraction?

The way I had success with casting, was casting a sheet of glass over a plaster refractory face mold. The mold shrunk more than the glass and it survived well. Casting over ceramic is hit or miss, depending on the shape. If the glass has somewhere to go as it contracts, it can live. If shrinking glass encounters not shrinking mold, and has no where to ride up, it cracks.
Bert

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rosanna gusler
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Re: challenges making a glass mask

Postby rosanna gusler » Wed Jul 01, 2015 3:53 pm

lots of issues including annealing. first off do you have air holes in the low parts of the mold? you need those. in order to get help you need to state the thickness of the glass and your exact schedule up and down. r.
artist, owner of wanchese art studio, marine finisher

roykirk
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Re: challenges making a glass mask

Postby roykirk » Wed Jul 01, 2015 5:50 pm

Thanks, Bert. Those are some good things to think about. You've intrigued me with the idea of a plaster refractory mold as opposed to using ceramic. I actually have a lot of plaster refractory around since I do bronze and silver casting. Maybe what might make the most sense is to print the mask, then fill the inside of it with plaster investment. Once hardened, throw it in the kiln to burn off the plastic mask (it's PLA plastic, so not hazardous). What should be left would be a plaster mask I could drape glass over instead if trying to slump it. I'm going to give this a try. :D

Tony Smith
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Re: challenges making a glass mask

Postby Tony Smith » Wed Jul 01, 2015 8:33 pm

Why don't you just print a negative image of the mask? Then you can pour the refractory into it and not worry about burning out the plastic.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Kevin Midgley
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Re: challenges making a glass mask

Postby Kevin Midgley » Wed Jul 01, 2015 8:36 pm

Graham Stone's firing schedules for glass are needed for a project like this to be successful over time.
the book itself will not give you a schedule, you will have to factor in all the variables to anneal properly.
Read it cover to cover several times to let it sink in.
This glass stuff is not the same as metal to work with.
:-k :-k :-k because you don't want it to crack a year later.

Dick
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Re: challenges making a glass mask

Postby Dick » Fri Jul 03, 2015 1:22 pm

silly question but did you kiln wash the mold first? If so, then probably a firing schedule problem

Morganica
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Re: challenges making a glass mask

Postby Morganica » Fri Jul 03, 2015 3:47 pm

Hate to say this, but what you're trying to do really is a challenge, and if you've never worked with glass before it's a bit farther down the road from a beginner's project. Certainly doable, but let's take this step by step.

First, kudos on the 3D printer making a positive that you used to make a ceramic negative mold. Exactly the right thing to do...but your first snag. Every part of that ceramic mold needs a negative draft to both accept the glass as it slumps down, and release the glass when it's time for removal (i.e., when you turn the mold upside down the glass should fall straight out without getting caught in an undercut anywhere).

Faces, though, usually have undercuts, so that may be part of the problem. (nasal passages, eyelids, etc) If your mask does, and you're going to continue using a ceramic mold, you'll need to eliminate those undercuts by filling them in or trimming them off.

When the glass covers the mold, it can trap air. If it does, the air expands underneath the glass, cushioning it and pushing it up, making it preventing the glass from dropping and filling in detail. You fix that by first drilling small holes in the lowest/most inaccessible points of the mold and, second, slightly elevating the mold in the kiln to allow air to circulate underneath the mold so the air can escape out the bottom.

As Dick mentioned, ceramic is a permanent refractory, i.e., it doesn't hit an inversion temperature and come apart with cooling. Permanent refractories need to be coated with a release or the glass will stick to them as it softens. Once stuck, uneven expansion/contraction rates between ceramic and glass will cause the glass (and sometimes the ceramic) to crack. So...you need to put a barrier of some kind between the mold and the glass. Typically, you paint the mold with several layers of kilnwash. Done correctly, you won't lose mold detail.

If you're worried about this, though, then you use the other option, as Bert mentioned, a refractory plaster mold. It will degrade with firing, doesn't need kilnwash, and takes detail perfectly. The downside is you need to make a new one for every piece--not a problem since you have your 3D printed mastermold.

The PLA burnout might be a problem--the residue from the burnout tends to leave deposits on the glass that can cause devitrification (crystallization), which leave a whitish, powdery surface to the glass. I'm with Tony; I'd just invert the model and print it that way. Or, depending on the 3D printer you have, and whether or not your hotend is interchangeable, you might try swapping out for one that prints with wax (there are some of these on the market; I'm futzing around with this now). The wax is fairly easy to steam out, which eliminates the devit issue.

Schedule-wise, it's going to depend on what you finally choose to do: Slumping or a thick casting. Either way, I usually have more control and get better detail in faces when I stay at low temperatures for longer process times. (And when I say "longer," I mean longer as in 3-4 hours). Would really need to see your schedule to be able to advise you.
Cynthia Morgan
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