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Wednesday, May 28, 2014

GAGU Casting at Spectrum Studios, Salt Lake City

Detail of my finished piece
As I've mentioned before, one of the benefits of membership in the Glass Art Guild of Utah is the opportunity for the guild to bring in instructors for group classes. Not only are we able to attract some of the best teachers in fused glass, but we also have a wealth of knowledge under our own roof.

Last week I had the chance to take a two-day, open-face casting class led by GAGU member Jack Bowman, assisted by Stephen Teuscher (also with GAGU) and "guest lecturer", Ann Cascarano. The open-face casting process uses clay to create a form over which plaster is poured. Once the plaster is dry, the mold is hardened in the kiln and then filled with glass and fired. 

I thought I would provide a few pictures of the process. Unfortunately, the only piece I have finished pictures of is my own piece (I couldn't make it to the final "unmolding"), but hopefully, you'll find the process interesting and informative, nonetheless.

We started with an 8"x14" slab of clay, that was roughly 3/4" thick. We could add to or take away whatever we liked, as long as we stayed within a few size guidelines so they all fit into the kiln. Following are a few of the initial clay pieces. The first one is mine, with pre-fired fused glass "fishes" I had made out of iridescent glass. 

Andie and Connie, working on their pieces
After the clay was prepared, it was time to encase the molds in plaster. As one person poured the plaster, another gently agitated the mix to keep bubbles from forming on the surface of the clay and to make sure the plaster was evenly distributed. 

Laying out the frame
Pouring the plaster

When the plaster was dry, we removed the clay (with the help of a few forks and knives to get it started, and then clay tools to finish digging out the fine details). The pieces were then taken to the wash station for a good rinse.
Amber, trying not to get too wild with the water!
Here are a few of the pieces cleaned, and ready to be dried in the kiln overnight.

Back the next day, and ready to fill the molds with glass. But before we can start, Jack shows us how we will unmold our piece once it is complete. 

The plaster breaks away quite easily.
The filling begins!
Filling (frit for the rocks)

Filling (more frit for rocks and river bed)

Filling (larger frit and glass)

Filled! (and ready for the kiln)
Here are some of the other pieces filled and ready to fire -- We're a creative bunch!

Little by little, the kiln was loaded with our pieces.

All in and ready to fire!
Steve, loading the kiln

Because of other commitments I wasn't able to join the rest of the group for the unmolding a few days later. I'm sorry I missed it -- all of the pieces were unique and I'm sure beautiful. Here's the result of my finished piece, however.

I'm very happy with the results. The rocks look like rocks and my "fish" sparkle. The rocks were a mixture of coarse brown frit, some medium terracotta, black fine, gray powder, and green fine. I knew I would end up either with great looking rocks or a muddy mess, but I wasn't certain which. Thankfully, I ended up with good results!

It was a pleasure learning from Jack, with the help of Steve, and also meeting and working with Ann. Ann is a warm person and fantastic artist. She created this wonderful piece while at Spectrum Studio.

Ann Cascarano, with her glass doors

If you are interested in learning more about open-face casting, you can always contact Jack at Spectrum Studio about his next class! If you can't make it to Salt Lake, there are also some great resources on the web:

Gerry Newcomb Casting Tutorial

Bullseye Education Video (subscription required -- their tutorials are well-worth the $39/yr)

Uroboros Kiln Casting PDF

Glass Art Magazine, May-June 2014 (part 1; part 2 in a future issue -- subscription required)

I hope this information has been fun and informative, and just the inspiration you need to get working with plaster and clay!

Happy fusing,

Learn more about Bullseye Glass Educational Videos!
Bullseye Kiln-glass Education Online


  1. Wow! this looks like so much fun, I am interested to know more about the plaster you have used and its ability to be placed in the kiln, is it a special refractory plaster? I am in NZ so would love to know if it is possible to purchase it down here?? Ang =)

    1. We used a 50/50 mixture of "US #1 potters plaster" and 325 mesh silica. Here in the US, the low-fire white clay, plaster, and silica can all be found at ceramic pottery supply houses. The plaster molds were dried at a low temp in the kiln overnight -- 200 deg I think (it hardens so the clay can be removed and the mold cleaned after 30 minutes).

    2. Thanks Dana for posting this. Though I only do small pieces, this gave me some good ideas. the blog is so clear and well illustrated.

    3. You're welcome, Barry. I would love to see what you do with this, if you try it out.

    4. Thank you so much for your generosity and efforts to share with us! Everyone's design looked terrific and fun. I am inspired to get busy with kiln work again. Much prosperity to you all! = )

      Reynal Art Glass Studio, Mesquite, Tx.

    5. You're welcome! I see you do a lot of beautiful stained glass as well!

  2. Hi I'm in the UK and came across your fab website.

    I am new to fused glass, having bought my first kiln as a Christmas/retirement present to me! I'm also new to your site and think it is really, really good and extremely useful. Great tutorial on cast glass which I'd like to progress to when I have more experience.

    Can anyone advise me? I've been searching everywhere online but can't find anything that tells me if I can use stone slabs on which to put my glass in the kiln: I particularly want a rough, natural and organic surface underneath my glasswork. I think I may know the answer; that it's not possible because of ... but can anyone help me with this?

    I've also been told that clay molds can only be used once, as I've considered using this. A source at a clay supplier here in the UK also told me that plaster of paris will explode in the kiln, so I feel that I'm going round in circles... or I am I over-complicating things?

    Can anyone help a novice?

    1. I don't know about using stone... I think you would have to worry about the stone exploding from the heat (I have no idea how much moisture it might hold...). However, clay molds can certainly be used more than once if they are coated with kiln wash. Some people also use paper clay, though I have not tried it. What little clay work I have done I have used low fire white clay.

    2. Good evening

      Thank you so much for your help on this. I'm determined to get to the bottom of this. I know that using stainless is the best, and most economic, way of using moulds but it would not give me the textured surface that I want.

      Interesting comments about the clay; I'll look further into this.

      Thanks again.


  3. I'm not certain who would even suggest that clay will not work. The majority of commercially-available molds for fusing are made from clay! You can make your own molds using low fire white clay, as I mentioned. As long as the molds are fired to 1500-ish (deg f) or so, they will be suitable for fused glass use. In general, as long as the molds are fired higher than the temperature for which you will be using them with glass you are OK. You might want to look at this post in

  4. Will do, cheers. I'll have a look at the link. I've bought some 6mm blanket wool fibre paper. This may give me what I need as I don't want substantial depth.

    Thanks again.