Wax Erosion

I've been demonstrating this technique in my classes this week: wax erosion. The short of it is, you apply wax in an image or pattern to bone-dry ware, then wipe with a sponge. Wherever the wax is will not erode, wherever the wax is not will. This creates a low-relief surface. You can do several layers - foreground, middle ground, background - for an illusion of depth.

Starts with a porcelain greenware cup

First layer of wax

I want to say a word about wax, here. I've used paraffin in the above picture, but the cup at the top of the post was made using water-based wax. The paraffin is harder and doesn't rub off as easily, but it has drawbacks too (besides fire danger) which we will see in a minute.

After rubbing with wet sponge

I wipe the surface of the pot with a wet sponge. The wax resists the eroding action of the water, while the clay around it gets worn away, leaving a raised pattern. Careful not to use too much water! If your greenware absorbs water too quickly it will crack.

More wax, on top of or around the first wax

More wiping...

Now, waaay over do it & wipe right through the wall of the pot!

You can skip that step if you don't feel like being a giant fuck-up. This, though, was the disadvantage of the paraffin wax; because you can wipe away a lot of clay before it starts to remove the paraffin, wiping all the way through the porcelain is possible. That would be a lot harder to do using water-based wax, because you either have to create a much shallower relief, or stop every minute or so, examine the pot, and re-apply wax where it has begun to erode.
Here are the two side by side! Water-based wax on the left, paraffin wax on the right.

 The wax - either kind - will of course just burn away in the bisque. I'm thinking celadon or clear glaze, or maybe just let the soda vapor do its thing.