Wax Figure prep for Casting

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.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s