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Monthly Archives: March 2012

After digging all the investment from inside the male figure, and realizing that the female figure would keep her solid core of investment- it was back to the pressure wash to clean the sulphur smelling black charr from inside the figure. Next I welded the arms, or what remained of them, and the one surviving window for the female fig’s calf. The day finished out with more than two hours of sandblasting, removing all the hydrocal-plaster tucked into every flashline, as well as the dark metal scale/carbon.

At this point we can really see what nice things occured in the casting. The male figure underwent a much harsher experience, attested by his surfacing and complete losses. The female figure poured nearly perfectly, with great crazing patterns augmented by the new idea of dribbled wax I added over the hydrocal layer.

Maybe I should let go of the idea of being able to dig out the core investment. This is how it is done for normal casting, but I should see how much more I can minimize that and still have the casting come out. For example, if I had removed her arms, the back of her head, and put more windows in her, then the flashing would not be cohesive and organic.

The goal of this process is a cohesive effect from the potential destructive/creative process inherent to casting, and pushing the destructive powers of molten metal and mold failure into a creative potential. The finely sculpted figure and the entire casting process are integral to allowing complete loss, or if all goes well, something unique that encompasses creation & destruction in one expression.

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The molds sat overnight to cool down, but were still piping hot. After hoisting the smaller form out of the sandpit, I rolled her out to the loading dock with the dumpster positioned below- and the restrained smashing began. Xmas smashing- with the investment as wrapping paper. The female figure came out well, with nice dense flashing honeycombing her head and tapering in intensity on down her body. Then it was back to the sandpit for the big fellow who poured with the fire-jet-eruption. He has very little flashing, as the bronze poured so hot it shrank back into itself making a wonderful pocked surface. He came out more intact than I expected. He is missing half his sphere and one arm- I think that area was too turbulent and the gasses won out over the bronze. One of his feet is partially missing as well. They are still full of investment, although I have removed most of it from the surface.

The superheated investment was charred and sulphurous. I have never poured bronze at that extreme of a temperature, and though the wax had burned out completely there was still carbonized wax in the mold. Next time I will only use the inner burners of the kiln, and close the vents down further- I’m certain I was getting a false read on the kiln temps from the outer ring’s heat jumping up the wall and out the vents. This is what compromised the larger form, as it had 4 more inches of girth than the smaller mold- so she burned out fully, and he was just under what he needed.  On a future casting I would like to ensure the molds are fully burned out, then let them chill down further so the molten bronze shocks them harder- and pour the bronze at least 100 degrees cooler.

Then I spent quite awhile putting the foundry back in order.

The figures are both out in my shop now, waiting for me to break out the chasing tools.

This post follows the process of three days: Saturday’s investing the 1/2 life size wax sculptures into tubes plastered to the floor with a mixture of plaster & sand & water, then loading them into a large kiln for burnout of the wax, prepping the sandpit, then a gap in the action while the big molds come to temperature and cool incremetally back down (46 hour burn); Monday we unload the molds while they are still around 500 degrees and bury them in the sandpit, fire up the foundry and begin melting bronze including two arms and a leg (but not the legs/torso!), and pour molten bronze into the mold (the largest form had a flaming jet, but the smaller form poured perfectly: we’ll see how it all turns out tommorrow when I dig them out of the pit and break away the molds.

The local supplier of Silicon Bronze (873 alloy) ran out a week ago, and finally today yesterday’s special shipment arrived. With no bronze in-hand I would have had to wait to burn out the waxes into next week, so I was glad the shipment finally came in. There was another issue: Bronze is running stupid-expensive at the moment. Just the bronze to cast two figures would have been close to $1,000. The last time I cast metal it would have been around $250. I was expecting prices to have doubled, but it was way out of the realm of justification. So I picked up enough to cast the smaller female figure, she is about 1/3 the mass of the male figure, and figured I would just have to leave it at that. Then I thought about the reject castings from my Orpheus and Eurydice commission for the Utah Opera/Symphony, partial bronze figures that I have dragged across the country with me for years . I had hoped to pull another two pair of legs to form a triptych base structure for a larger work this spring, but that can never happen with bronze prices so high. Instead I will cut these pieces down and re-melt them for the large male figure.

Also pictured are the investment forms for the two figures, created from chicken wire and tar paper. Tommorrow, with the help of a student volunteer, I will interr the wax figures with the investment slurry and load them into the burn-out kiln, starting 50-odd hours of baking to melt out the wax and vitrify the molds. I’ll be driving up to check on the kiln every few hours the entire time- if the temp bumps up from 975 up past 1100 as the molds dry out, then the molds will weaken or fall apart, so temps must be held constant, and must be lowered incrementally or the molds cool too fast and split or shatter.The bake times out at 10am Monday, and guestimating it will be cool enough to remove the molds for a noon/1ish bronze pour.

 

As I am teaching up at the University this semester, I have an opportunity to cast again. It has been more than 10 years since I have cast my own work, and in that time I have created two figures that I liked enough to pull molds from- the woman and man with heavy ball that I finally cast in bronze at the foundry last spring. That was done in ceramic shell, and ensures a perfect cast. At the University I will cast them using Investment Molds, which allows me to cast the full figures at once instead of cutting them into little pieces as must be done for Ceramic Shell. Both arms of the male figure, and one arm of the female are cast separately, as they are molded separatley- and the holes in the figure allow investment slurry to flow inside the figure. I will push these figures as I did with my MFA work, setting up a condition to create crazing and flashing over the entire figure.

The past few millenia have been dedicated to pulling these two 1/2 life size figures in wax and prepping them for bronze pour. The first step is painting layers of wax into both sides of the mold. When casting with the industrial foundry I have them pull the wax figures, which they do by pouring wax into the molds and having a few guys roll the wax around inside the mold as it chills to a consistant 1/4-3/8 inch thickness. I can’t heat up that much wax, or coat the inside as evenly- so I paint in the wax for each side of the figure, slowly building up to thickness, then pop each side out of the mold and seam them together. This method takes a whole lot longer, and the outcome is never as good because the wax seam issue.

Once the wax figures are chased out and pretty, I cut windows as minimally as I can to ensure the mold fills the interior of the forms. Next I sprew them for casting (the little red-wax connections). Sprew Gates allow the path of molten bronze, while Sprew Vents allow air displaced by the bronze to escape- this ensures that the entire form will cast evenly.

Next I drill tiny holes all through the figure and seat finish-nails half in / half out. These will act to pin the interior investment mold to the exterior investment, keeping the core from shifting.

Then I do something out of the ordinary for Investment Molding and flick-coat the figures with plaster. This time I also drizzled some hot wax over the plaster. This layer will shatter when the molten bronze hits it at 2,000 degrees, and jump toward the small spaces of the wax drips, allowing spontaneous and unique surface crazing and flashing. This captures the fleeting crucial moment when the figure shifts from a delicate hollow nothingness, to molten bronze.

The last step is adding on the pouring cup with multiple legs of sprews to channel bronze into the figure, and a smaller secondary wax cap for vents to collect at (also acting as a back-up pouring cup, inverting the vents to gates in the case of a fail).

If all goes well, I will invest them on Saturday and put the forms into a large kiln for a few days at 1,000 degrees to burn out the wax and vitrify the molds. Then I’ll pull the molds while they are still incredibly hot, flip them over and bury them in a deep sand pit, heat up aournd 120lbs of bronze and pour it down the hole. If that all works out, then 12 hours later I pull the forms out of the sand pit and smash away the investment and see how things turned out. If it went well, then on to cutting off the sprews & gates, then welding things together.