Glass casting (or: what I've been doing on my summer^H^H^H^H^H^Hfall vacation)

[Arcy]

Hi all,

I haven't been around for the past while because I've been back in the glass studio, taking a glass casting class which has been seriously monopolizing my time.

Jerry made me promise to post pictures, so Jerry, here they are:

I've been doing a few types of kiln-based work (not blowing in the hotshop): fusing (more or less where flat pieces of glass are cut, assembled into a pattern, and then heated up until they fuse in to a single sheet. they can then be further "slumped" in a mold) and kiln casting (where a mold is created and glass chips is melted to fill the mold).

Here are a few pieces I've made with the fusing process.

The plaque is glass frit (very small bits of crushed glass) with cut glass overlaid and all "tack fused" together at a temperature hot enough to make the pieces stick but not to melt completely into a flat plate.

The bowls are also frit, tack fused into a circle and then slumped into a bowl forms.

[Arcy]

Casting is more complicated.

We start out with a model, then create a plaster mold from the model.

In my successful examples, this was made of clay, but (obligatory scrollsaw material) I did attempt to make a plaster mold of a small 3-piece puzzle I had cut. Unfortunately, when I poured the plaster I couldn't release the model from the mold and so ended up with a brick.

Here are the clay models in a mold form ready to have the plaster poured.

The bodies are ready to have plaster poured for a one-piece mold. The limbs are half dammed off with more clay to prepare to make a two-part mold so they can have undercut curves (plaster around the top, then remove the dam and plaster around the other side). The ring has the first half a a two-part mold poured and is ready for the second. The extra clay sticking off the ring is to create a pour-spout so that the mold can be filled what whatever we're casting (in this part of the process: wax).

[jim_mex]

Hey Rob - you have been busy!
I like the bowls, particularly the spiral one. It reminds me of Bassetts Liquorice Assortments, one of my favourite sweets as a kid, Don't know if you get them in your neck of the woods but they were basically made from sheet liquorice wrapped around brightly coloured soft sugary candy - yummy. I also like the fusion technique you used to give the globules effect. Neat!

Thanks for sharing - its great to see what else scrollers get up to!

update cos we were cross posting!

Unfortunately, when I poured the plaster I couldn't release the model from the mold and so ended up with a brick.

Been there and done that many times! Enough mistakes and you either get better or give up! Stick with it pal!

[Arcy]

The plaster molds can't stand the heat, and so can't get the glass directly. Instead, we pour wax into these pattern molds and then clean up and assemble the wax into a second temporary model (one can also work directly in wax without the initial pattern mold).

Since I was aiming for shapes that were too complicated to create a reusable mold in, I made molds of the various parts to assemble afterwards. I used a fairly pliable wax, so I could bend the pieces into shape and pose them.

[Arcy]

Most of the mold making happened in various levels of outside: the wax pouring was in the garage, but the plaster (and the upcoming silica-plaster) was done outside. Silica is nasty stuff (Silicosis - Wikipedia, the free encyclopedia) which you don't want to breath. Even with a dust-mask, I didn't want it inside. It's getting a bit late in the year for outside, and since I'm new at all this many steps took longer than I had planned. I ended up working until (in at least one case) past dark and in winds. Fortunately, I managed to get in before the rain started!

I assembled the wax pieces into the actual models inside, which ran into other hazards:

[Arcy]

The black marks on the wax models are carbon from the candle I used to heat my tools. It's a bit ugly but won't make a difference in the final product. Ideally I'd use an alchohol lamp for a cleaner burn rather than a candle, but I didn't have the right stuff on hand. I definitely wasn't using my Don Julio (at least for the burning - it did help my mood!).

The cones they are standing on are feed tubes for the glass to enter the mold through later. The bamboo sticks in the dancers are air vents, so that bubbles won't form in the areas that the glass will have to flow up into.

[Arcy]

We can then make a one piece plaster-silica mold around the wax model. By using a mix of plaster and silica the mold can handle the heat of the kiln. Surrounding layers add sand and grog (pre-fired clay granules) to add strength.

Since these were the first I made, and since I missed the class where the instructor would have helped, they aren't great. I definitely made a few mistakes here, but that's how one learns!

[Scrolling Days]

Hey, Rob! I was just thinking the other day that I haven't heard much from you since National Talk Like a Pirate Day!

It's good to see you're doing well and just having fun getting into other stuff. I can tell you're enjoying it. Please keep us up to date on your projects.

Love the cat pic, LOL!

[Arcy]

Of course, now that we have a mold with wax in it there isn't anywhere for the glass to do. Fortunately, wax melts: setting up the mold over a steamer lets it all empty out. It can then be inverted (hence the flat "top") and glass added through the feed tubes.

[Arcy]

Through a complex mathematical process we can calculate the amount of glass needed (ok, not so complex: measure how much water fills the mold and multiply by 3.76 to get the weight of glass to fill the same volume) and put that much glass in clay flowerpots placed over the mold in the kiln.

The kiln is closed up and brought slowly up to temperature so the glass melts and can flow through the hole in the pot and into the mold. We hold at that temperature long enough for the glass to fill all the nooks and crannies of the model, and then very slowly (over several days - longer for very thick pieces) lower the temperature. This needs to anneal slowly enough that the entire piece can equalize temperature and relieve stress as it goes: if the inside is hotter than the outside it will crack later.

The blue in the center back of the kiln are my rings. The rest belong to others in my class.

The dancers didn't make it into the kiln. After discussing it with my instructor, we decided that they'd be better as separate pieces. The attachments between them would be too fragile and they would be extremely difficult to coldwork (grind & polish) later without breaking.