I’ve got a pretty busy week going on here. Opening tomorrow, Thursday the 3rd, I’m going to have a little minishow to celebrate my signing up with Gallery IMA. This little preview show is going to be in their lower gallery, and will feature a few of my ceramics and one bronze. I’ll be around during the gallery opening from 6pm to 8pm. It’s an excellent gallery. You should come on by and check it out! They’re at 123 South Jackson Street.

The other big thing is this Saturday from 6pm to 9pm is the biannual Open House at the Pratt Fine Art Center. The open house features refreshment, good times, live glass blowing and art demos, and most importantly for me, a bronze pour. As folks who’ve been following my work recently might know,  I’ve been working on a complicated antelope style beast along with a pair of antlers for my large woodfired beast. Both of those will be cast in bronze this Saturday. There’s quite a few sculptures ready to be poured, so we’ll be doing two melts (two rounds of melting and pouring the bronze). The timing will depend on the metal itself, but we’re aiming to pour the first crucible of bronze at 6ish, and the second at 7ish. The pours themselves don’t take that long, so give yourself time to spare to park and navigate. About 20 minutes after the second pour, we’ll start breaking out the pieces, so you’ll be able to see everyone’s work, then and there!
Pratt is located at 1902 South Main Street, Seattle. The foundry is in the building next to the park, along with glass blowing, forging, and stone carving. Hope to see you there!

Awhile ago I wrote up a post about preparing for bronze casting. It tackles creating a clay sculpture, making a mold, creating a wax version, and preparing the wax for the investment process. Since I’ll be doing another bronze pour this weekend, I thought now would be a good time to follow up my first post with a talk about the rest of the process: the investment, the casting itself, and the initial clean up.

By the end of the last blog post, I’d followed my sculpture up to the point where it was this crazy chrismas tree of wax, with wax sprues existing to give the bronze a path to flow down in the sculpture, and additional wax vents where the air will flow out. There’s actually a few options at this point. There’s a process called ceramic shell casting, where you build up the mold in layers. It’s neat, but something you need a dedicated facility for.  Our class, on the other hand, went for the classic method of investment.

“Investment” can refer to the finished plaster mold, the plaster and sand mix you use to make the mold, and the act of imbedding the wax in the investment. It gets a bit messy, both in phrasing and in reality. Anyway, you make your investment by creating a cylinder of chicken wire, for reinforcement, and then a cylinder of tar paper, both a few inches larger than your wax in every dimension. These act as molds for the investment mixture. We used two scoops of sand to one of plaster for our investment, but the mixture can vary. The first step is to pour a couple inches of the mix into the bottom of the tar paper cylinder. By letting this harden before adding the rest of the plaster, you’re less likely to have liquid plaster escaping the mold and covering the whole floor. Less likely, but not guaranteed. It’s a messy process, as I said.

Once the bottom of cylinder is a bit set up, you fill the rest of the form all the way up with the investment plaster. You carefully lower your wax form down into the plaster, jiggling it to try and dislodge bubbles that might stick to it. There’s various ways of keeping bubbles from adhering to the form, ranging from spraying the wax with a thin coat of shellac, to shaking it, to raising it up and daubing at it with a brush. It sounds like each bronze caster has their own way, each convinced of its primacy. Regardless, the final step is to carefully hold the wax in place until the plaster is set and the investment is complete.

At this point we made sure to label our investments, since they all look awfully similar. You can see the pour cup in the center, where the bronze will eventually be poured, along with the red wax vents on each side.

After the investments are set, the tar paper is removed and they’re loaded into the burnout kiln. It’s during the burn out that lost wax casting finally lives up to its name.The investments are placed upside down, so that the wax flows out. However, you want to go significantly hotter than the melting point of wax. This is so that any wax that remains is vaporized, and any carbon left from that is burnt out. Here, we’re vacuuming any dust this might have ended up in the investments, before carefully setting them up for the casting. Keeping the insides of the molds perfectly clean is critical at this point. Anything in the form will end up embedded in the bronze, or causing bubbles if it’s flammable.

After the molds are lined up in the sand pit, the casting can begin. They use a crane to lift the crucible up, and then take the time to skim some impurities off of the top. Mark, the instructor, is carefully observing each mold, watching to see the bronze flow up into the vent tubes, indicating that it’s full.

Here’s another view of all the molds lined up in the sand pit. At the end, they pour the extra molten bronze into ingot trays, so they can melt it again next time. In reality, the molten bronze is a beautiful golden color, one that the camera can’t capture.

A mere half hour later, we began to remove the investment. As someone who’s used to waiting a week for the wood kiln to cool, this sort of turn around is nuts. The pieces were still quite warm, but nothing that thick gloves and some cold water couldn’t deal with.

The pieces, as they came out of the plaster, looked more like something you might expect to see in Pompeii. Next up was a mass of washing, scrubbing, and finally pressure washing the pieces at a car wash.

Even with the pieces out of the mold, the work was only beginning. Each bit of sprue and vent had to be cut off with a die-grinder, and ground smooth. Flashing, thin lines of bronze that form where the mold fractures, had to be removed with a chisel – likewise with many tiny bronze bubbles. It’s always a balance between how much you want to shape the piece post casting, and how much you want to keep the original texture.

In the post about the wax making process, I explained how any hollow piece had to have an opening, to let the investment enter the piece. This is now the flip side of that. Ever piece with a little hollow body, must now have the the lid welded back on. One of the instructors was helping out with a TIG welder, carefully doing touch ups where needed. Since we were allowed one or two investments, most folks had one or two pieces, with maybe one spot of welding. I had nine, each with tiny lids. When he was finally done welding them, I bought him a six pack of beer.

The real kicker is that even with all of that work, I’ve only really been getting started with these bronze beasts. It turns out that there is no end of possible patinas for these guys. The only ones I’ve declared finished are the first set of odalisques, which I polished to a high gloss and sealed with wax.

I’ve been working my way through The Colouring, Bronzing and Patination of Metals by Hughes and Rowe, and I have no end of experiments to try.  The most amazing thing about patinas to me is that I can simply sandblast away any I’m unsatisfied with, and start anew. I’ll be casting a dozen tiny pieces this weekend, just so I have more beasts to experiment on, and I have shipment of chemicals headed my way as well. I’ll eventually put together a blog post on patination, but in the mean time you can follow my experiments on twitter.

This summer, I decided to follow up on something I’d enjoyed in college, but hadn’t had a chance to explore further – metal casting. I signed up for a class at our local Pratt Fine Art Center, and spent several weeks building waxes and eventually casting a small set of bronze pieces.  While I’m taking my time finishing up the finished bronzes, I thought I might write up a bit about the process in the meantime.  It’s such a massive process, I decided it would make sense to cover it in two halves: creating the waxes, and investing and casting them. At some point in the future, I’ll try and write a bit about my experimentation with patinas, but I’m only getting started with that. In the mean time, I’ve collected all the pictures of the process into one set on flickr.

As the name suggests, in lost wax casting, you create a form in wax, sink (invest) that form into plaster, turn the plaster mold upside down in a kiln, cook it until the wax is all melted out, and then you pour the bronze into the void left by the missing wax. It’s a pretty straight forward method, but it means that you’ll be spending quite some time getting everything just right with your wax form. I’m OK with this, since it’s easier for me to fix wax than to fix bronze.

While you can sculpt your form directly in the wax, it’s more common to first sculpt your piece in something else, such as clay, and create a mold from it. This is because ideally, your wax form will just be a shell of 1/8″ thickness or so. Any extra wax used will result in extra metal being used in the casting, making your piece heavier and more expensive.

Most artists will sculpt their forms out of solid clay, perhaps over an armature. I decided to cast two sets of work. The first set was to be three sets of three fat, little odalisques – I decided if I was going for bronze, I’d go to the classics for inspiration. The odalisques I sculpted in my normal fashion – hollow, built up starting from two little pinch pots. The second form I went for was built solid, with metal armature in the legs. I’ve been calling him The Walker. I don’t have a final title for him since I still need to put some finish touches on him. For The Walker, I decided to create a mixed media beast – a clay egg, a leather belt holding it on, and perhaps clay feathers surrounding it. I knew bronze would give me a chance to make legs longer and thinner than I ever could in woodfire. It also was going to be a interesting to make a mixed media form where I wouldn’t have to worry about shrinkage. My clay shrinks 14% or so, but the wax will be identical to the bronze. If I fitted the wax beast with finished mixed media parts, the same parts will still fit on the finished bronze.

For the Odalisques, the mold making was extremely straight forward. There an almost no end of different mold materials out there, ranging from commercial two part rubber mold kits to old school plaster.  The material I used primarily was silicone caulk, specifically GE Silicone II (not I). It has great fidelity, is easy to use, and is quite cheap. The main downside seems to be that it stinks to high heaven. Pay attention to ventilation if you try this. Anyway, Silicone II can be applied directly to clay, and then peeled off later. If you apply it to some other materials, like metal, you might need to put a coat of Vaseline on first. By applying three 1/8″ coats of Silicone II, you can built up a fairly respectable rubber mold. For each of the three odalisques, I embedded them on a pole to hold it still, and then built up a bit of extra clay around the pole. In this silicone mold, this represented the opening through which I’d later pour in the wax. I removed the finished mold by slicing it slightly with an razor, just enough to pull the mold off the clay. Later when I poured in the wax, I could stabilize the mold just by holding it in one hand as the wax cooled.

The mold for the Walker was a bit different. Being such a large beast, I cut it into sections, and made individual molds of each leg. The body was also given a silicone mold. However, the body was large enough that the silicone mold would have been too wobbly to use without some sort of reinforcement. Therefore, I made a “mother mold” out of plaster, that would surround the silicon mold and hold it steady as the wax was poured in.

Bronze casting is interesting. The joke folks were making in the class is that is that it’s three times the work, for one third the finished pieces. First you sculpt it in clay, then you sculpt it again in wax, then you sculpt it one more time in bronze. I suspect the better you get, the more streamlined the process is. However, as a novice, that was definitely true for me. Once the wax forms were cast, I had to repair and reassemble them.The spouts where the wax had been poured into the molds had to be removed and patched over, and the legs of the tall beast reattached. It took a lot of fiddling, but eventually I got to the point where I had a finished version of each piece.

However, once you have your wax piece finished, there is still a very critical step to undertake before your piece is ready for investing in plaster. You have to sprue and vent the form. Early on, I explained how the wax form would eventually be transformed into a void in the plaster mold, one that will be filled with molten bronze. The sprues are the attached pieces of wax that will act as channels through which the bronze will flow to reach sculpture. For some reason, sprue wax is often red. It’s still wax, though. Vents are related to sprues. They’re attached to give air an exit path as the bronze is poured in. You have to consider how to sprue and vent the piece to insure that the bronze flows smoothing and evenly through out the whole form. This was fairly easy to accomplish on the Walker. The little odalisques, however were a bit more complicated.

One other aspect of the getting the pieces ready to be invested is that if the forms are hollow, you have to have an opening where the investment can flow inside of the forms. For the little Odalisques, this meant I had to cut tiny lids in their backs. You can see how each is being attached to the sprue tree, like tiny delicious brussels sprouts. The investment will flow into each opening, ensuring the bronzes stay hollow. However, this also meant I now had nine tiny lids to sprue and vent, along with all nine odalisques.  The lids will be welded back on, after casting, using TIG welding. However, that’s something I’ll cover in the second post – investment and beyond!