Sunday, March 26, 2023

tetsubin: experiments in mold making for cast iron

This weekend I've been working on a cast iron teapot that I cast several months ago at the WNC Sculpture Center. I have been to several pours there since the beginning of the center, but I had been to one for a while. I work with Joe Bigley who teaches Foundations and the occasional sculpture class at AppState and he runs the sculpture center there. 

This teapot is an extension of some of the bronze and aluminum teapots that I have been making. Since these teapots are an extension of the design and patterning, and inspired by my interest in traditional Japanese cast iron tetsubin it only seemed fitting to do a series in iron. I have been hesitant to cast in iron, as most everything I have ever made in iron has either been too heavy or the objects themselves just didn't turn out. Not to mention the cleanup is always a pain, and I really hate the grinding dust created from iron.

This particular casting turned out exceptionally well though. I attribute this to my pattern and mold making process. First the teapot pattern was created using a 3D printer and I could really control the thinness of the pattern and not have to worry about burn in from a sand mold due to my use of ceramic shell for the initial coats of mold. I have been using traditional investment for a lot of my most recent cast work simply due to the ease of getting the materials in Boone along with the fact that I have had spotty results with the use of ceramic shell due to humidity up here in the mountains. Ceramic shell requires a lot of drying time in between coats and I was having to wait almost a full day to get a layer to dry (that said I have some ideas about solutions for this). Normally I would apply eight coats of ceramic shell to build up the thickness of the mold and insure a strong mold. In this particular case I utilized 3 coats of shell and then I poured traditional investment around the mold. Traditional investment is not suitable for casting iron at all. The plaster normally would not be able to withstand the excessive heat of the iron and would simply melt. By using ceramic shell as an initial mold facing and insulator, the iron is kept from contacting the main mold (assuming you don't have cracks in the shell) and all is well. I was dubious about pouring iron in these the day of the pour because I was not certain three coats were enough of a barrier AND I'm not able to inspect the mold for cracks before pouring since the entire mold cavity is incased in traditional investment. I will add that I burned the molds out for a few days before the pour and took the molds to the pour and they were still quite hot. I actually had to put down a heat barrier to transport the hot molds down the mountain to Joe's place. The molds were still quite warm when I placed them on the pour floor, so i believe the insulation of the investment around the shell was helpful for pouring into a semi-warm mold as we would usually preheat ceramic shell molds before pouring; something I wouldn't be able to do by hitting the traditional investment with a immersion burner. Regardless, the pour went well and I walked away for the night to return the next day to the molds. I broke open the molds and I was immediately surprised by the ease of shell removal. It just flaked off unlike some of the recent shell molds I've made. The other thing I noticed was how clean the surface of the iron was. There no signs of chilling and I after subsequent clean-up the iron materials consistency seems to be uniform. A lot of times I have noticed hard spots in iron that I cast in a similar methods, but this pieces seems to have cooled very evenly. Again, I believe this is due to the traditional investment mold mass that insulated the piece after the pour, and allowed it to cool very evenly and slowly. I also believe my patience in opening the mold also assisted in this most likely. I usually break things out too fast and I believe this effect recrystallization of the metal.

Needless to say, I have many more tests to conduct before I can confirm all of these findings, but for the time being I am now thinking more about cast iron objects in my future. I have the Sloss conference just around the corner. I will see if I have any time to make some more experimental molds for the event, but if not, I'll try to get down to another one of Joe's pours soon. In the meantime, I'll keep cleaning this piece u and working out the finishing details. I'm looking forward to seeing this one completed and documented.


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