Monday, January 19, 2009

A clever tool

I thought I would share some of the problem-solving that has gone into making Imp in ceramic. Each horse presents different production challenges. In the case of Imp, most of them have centered around his size. Just a few years ago, we thought stablemate-scale sculptures with thin legs were not feasible. That's one of the reasons there are so many draft and pony breeds in ceramic; they have relatively thick legs. (Well, that and many of us working in ceramics are Anglophiles.)

We have gotten a lot better at dealing with thin legs, but problems remain with small horses. When earthenware horses are cast, liquid clay (slip) is poured into the mold, allowed to sit until a skin is formed, and then drained back out. As a result they are hollow inside, somewhat like a chocolate Easter bunny.

The goal is to get a fairly even thickness to this "skin". Excess slip can't stay inside the body of the horse or the barrel and hindquarters suck in during the drying period. Those larger areas must drain back through the pour hole. This means that the pour hole opening has to be large enough to drain the slip even after the skin has formed around the opening.

With most horses, this isn't a big problem because they aren't poured very thick. Imp is different in that he must be poured a little thicker, otherwise the area around his throatlatch closes off, leaving an air pocket inside his head. Air pockets that don't vent to the outside can cause a piece to explode. The idea of opening a kiln to find a half-dozen Imps with their little heads popped off was really unappealing! The solution was to wait longer to drain him so the inner walls would be thick enough to make his head solid.

The problem with this was that his pour hole - the spot where the clay had to drain back out - was already too small. His belly just wasn't wide enough to hold a proper sized pour hole. Walls thick enough to fill his head closed off his pour hole, but weren't so thick that there wasn't excess slip sloshing around in his belly. I needed to be able to clear the pour hole so it could drain.

Unfortunately just sticking something up inside doesn't work well. It's hard not to push through the pour hole and on into his back. Since the mold turns upside down to drain, the damage to his back would not refill. What I needed was a special tool just long enough to clear the pour hole, but too short to hit his back.

I needed something that could scoop the clay out of the opening, rather than just push it around, so I used my round-nosed pliers to make a loop from some armature wire.

Here I've used the rubber master to determine the length needed. I want the loop far enough inside that I'm not scraping it against the plaster mold. The metal wire is hard enough to chip the plaster. I want it just a little beyond the opening, but well away from the topline.

After marking the length I need with a Sharpie pen, I bent the remaining wire into a handle.

Then the handle was covered with polymer clay and baked. This stablized the handle and allowed me to hold it a little better. (The purple handle has also make it harder for me to lose the tool, which has made me wonder if I should paint all my tool handles bright colors!)

Since making the draining tool, I've been getting a higher percentage of Imps that survive to the bisque stage. Now my only production question is if I can get them to the final glazed stage.


mel said...

Purple tools! Awesome! Makes me want to put purple handles on absolutely everything!

Joanie said...

Great idea, Lesli!I love the handle. Very fun and useful.


Becky Turner said...

I did this a long time ago on some of my sculpting I had some scraps of different colors sculpey so i twisted them up and made handles for some of my tools! sculpey can have lots of cool uses! .. good idea Lesli! cant wait to see the imps fired and glazed!
Rebecca Turner

Speiser Studio said...
This comment has been removed by the author.
Speiser Studio said...

Sorry, the Delete was mine since I cannot spell :)
Thanks for the Great posts in your Blog!I have read everything on here :)
I am one also that needs to paint all my tools bright colors!

Lesli Kathman said...

I'm glad I'm not the only one! Although really what I need are those little chirp things they put on your keys that let you find your car in a parking lot. I need one for each of my tools, my eyeglasses, and my keys. :)

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