My goal is to have made at least one tiki mug for my home tiki bar, by the end of the year. I’ve been poring over Tiki Central’s forums to learn more about the process. I have also picked up a couple of books on it, and have been creating a big workflow list of all of the tips and tricks I’m finding so far.
Yesterday, I finally rented a car and drove down to Seattle Pottery Supply, to try to get my brain around slip casting materials. It was… a little overwhelming. After asking a couple of other employees, eventually one lady there, more experienced in slip casting, gave me some pointers to get going. (Sadly, I didn’t catch her name, or I would thank her again here. That said, everyone at SPS was very helpful.)
- She recommended creating my master sculpt with water-based clay, because the wax and oil from the Monster Clay (that I was going to use) will clog the pores in the plaster mold, causing it to take much longer to soak up the water when casting. Seems like the speed of casting isn’t really a critical thing at this point in my learning (I’ve certainly seen other people on Tiki Central use oil-based clays for this), but I’ll give it a shot. Sculpting with water-based clay seems different enough from the oil-based that I was using, that I suppose I should get used to doing it “the right way.”
- Reading this the day after, am I supposed to wait until the clay is dry to mold it? Make sure it’s still wet? Forgot to ask this question, and I’m afraid that if the clay is dry, it’s going to stick to the plaster.
- For this same reason, she recommended against using mold soap on the master positive. Only if there’s a multi-part mold, and then only on the plaster-to-plaster seams. While the mold soap can be washed off to some degree, some will always remain in the plaster pores and cause extended slip casting times.
- She recommended working in stoneware slip for the tiki mugs, as they will chip less easily than earthenware. She sold me their “Swan” casting slip, which fires at cone 04-6 (I assume that means cone 04 for bisque and cone 6 for glaze (glost?) fire? I should have asked.)
- She also recommended National Artcraft Co. Casting Rings for determining when to dump the slip from the mold. These rings come in 7 different thicknesses (she recommended #4 for mugs). You set the ring on top of the plaster mold (number side up), just next to the pour hole, and fill the ring with slip. When the button of slip inside the ring becomes leather hard, the mold is ready to dump. She said differences in humidity and plaster density (not to mention moisture from casting multiple items in a row from the same mold) can change the amount of time required for the slip to build to the thickness you desire, so this “button” method is more reliable than setting a timer.
- Once I get to doing multiple castings at once, she gave me this tip: instead of buying many copies of these $5 casting ring sets, find washers at the hardware store with the same interior diameter, and glue them together to match the height of the ring number I want to pour to. All you basically need is a little ring-shaped dam to keep the test slip on top of the mold.
- The rings seem to be in roughly 1.5mm increments, with a 14.5mm average interior diameter. (All of the rings are a little sloped so they have a larger diameter at the bottom; the shortest ring has a 14mm inner diameter.) Ring #4 is 6.05mm tall, according to my micrometer. That means two glued-together washers of USS size 1/2″ (which actually have an inside diameter of 9/16″ / 14.29mm) will be close, if a little thin (5.54mm height for two washers). Maybe the glue will make up the difference. 😉
- I picked a single glaze for the test medallions: Duncan RG722 Sea Glass, which says “fire to cone 5-6”. The sample there showed it coming out as this aqua green sand-tumbled Coke bottle kind of finish, though a bit more glossy. Should look nice on what I have planned for my test medallion. She recommended a fan brush with a rounded ferrule to evenly distribute the glaze, if you’re not doing small areas of different glazes. Water cleanup. “Everything’s water cleanup with clay,” she said.
- I also grabbed a couple of Kemper sculpting tools, including one with soft rubber tips, which seemed useful for smoothing the edges of relief elements onto a mug/medallion surface. These wood handles are way nicer than the unfinished ones that came in my $10 beginner’s kit from Amazon. I already feel the Kemper lust forming in my heart.
- For plaster mixing, she recommended a Jiffy Mixer drill attachment, which she said would help prevent air bubbles from getting into the plaster. “Submerge mixer into materials to be mixed before starting motor; shut motor off before allowing mixing unit to reach surface of the mixed materials.”
So, of course, I came home with more clay and plaster and glaze and other assorted tools. I plan to start with some small medallion/pendants first, just to get a feel for the process. Wish me luck!
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