Friday, July 01, 2011

Last night I did a workshop in our studio on layered underglaze/colored slip surface decoration. It's a technique I learned when I attended The Surface Decoration workshop through the Potter's Guild in Temple, TX a couple of months ago.

I've been playing with the technique all week and have become incredibly inspired by the process. I'll walk you through the workshop so you might become inspired as well.

Here's the initial setup for the workshop. From the left side: slab prepared for platter demo, tile prepped for technique demo, sample stencils/sample patterns/heat wire, plaster molds, samples of finished pieces using technique. Please ignore the soft drink in the photo. It's not mine.

This is the stencil I used for the platter. It's adapted from a Judaica papercut. Papercuts are, for all intents and purposes, stencils. After sizing it correctly, using Picasa software, I traced it onto my .010 Lexan and cut it using a stencil heat wire. I'd say the stencil took me about two hours total, from printing to finished piece.

First I did a demo on a tile I had prepped earlier. (Everyone had two tiles to play with -- everyone only had time enough to complete one.) The prep involved painting black underglaze on the surface of the tile and allowing it to dry to matte consistency, while keeping the tile itself moist and pliable.
 I began by carving a series of angled lines as a backdrop. The lines will fire the color of the clay which, in this case, is low fire white.

You could just as easily make swirls, geometric patterns, or not carve at all. But the technique is about layers, so I carved.

 Being a little bit OCD in the studio, I used a ruler for my lines.

Then I took a stencil (a commercial one in this case) and used a rolling pin to embed it into the clay. 

The idea is you want the clay to come up so its surface is level with the top of the stencil. This will prevent your underglaze or slip from bleeding, giving you a crisp, clear image.

Because I used a black foundation color, which muddies overlying colors, I put a base coat of white underglaze. This acts the same way a primer does, helping your lighter colors pop. If you're going from light base to dark, this step is probably not necessary.

Then we had to "hurry up and wait" for this base layer to dry to matte. When the tiles are done, and dry enough, they'll be placed on a plaster slab and rolled over, to flatten the design side. It's important to compress the layers, leaving a smooth surface. This decreases your chances of cracking along stress lines created by carving and raising clay through the stencil/s.

At this point I had everyone base coat their tiles with the color of their choice.

While all the tiles dried I moved onto the platter demo .

Remember the stencil in an earlier photo? I used it for this platter. Since the stencil would block the pattern, I used Fossil Gray Amaco Velvet underglaze, which would give me a stonelike effect. It's fires gray with tiny black spots. 

When that dried to matte, I rolled on my stencil and used Medium Blue over it. This was the result when I peeled off the stencil.

I placed my "Shabbat" (in Hebrew, since I do Judaica) stencil over the centerpiece of the slab, trying to center it correctly.

Then, just as on the tile, I used a roller to fix it into place, again making sure the clay came up level with the top of the stencil.

Using black underglaze, I painted on a couple of coats and waited for it to set.

It doesn't need to dry completely before removing the stencil. It just needs to set enough so it won't smear.

Here it is, with the stencil removed.

Throughout the process, it's important to make sure your slab remains pliable. I do this by spraying plastic and laying the slab over that. Then, periodically, I pick up the slab and spray some more. Since the slab is about 1/2" thick, this keeps the clay pliable, while still allowing the surface colors to dry.

Once my underglazes have dried so they're no longer tacky to the touch, I cut out my platter.


Now let's backtrack a couple of steps. While I was waiting for my underglazes to dry, I took a plaster hump mold and centered it on a foam bat. I'll be using this to shape my platter.

Here I've begun shaping the slab against the mold using a rubber rib. You could just as easily use a wooden one. The idea is initially to use lighter pressure, molding the clay to the shape of the mold.

I slowly increased pressure on the clay, both compressing the piece and trying to flatten out the textured layers from the carvings and the raised stencil parts. This is to prevent cracking from multiple sources: not enough compression of the slab (especially on a larger piece), stress from the carvings and raised lines from the stencil. This also gives a nice, smooth surface to the inside of the functional piece.

Compress, compress, compress.........

When I feel I've finished compressing, I take a serrated rib and score the bottom where I want to place my foot. I do this while the wheel is moving, making it simple to be sure the foot will be centered. The step missing here is that I trimmed the rim of the platter with the pointed tip of a sculpting stick. Then I used a damp sponge to smooth off the sharp edge. Then I just trimmed up a little along the inside. I smooth that off when the platter is removed from the mold.


Then I put slip over the scoring. I'm using slip made from my clay body with water and a little vinegar to act as a flocculant.

I've made a coil using a handle cutter. You could just as easily roll one or use an extruder. I've scored the coil, slipped it, and joined it to the bottom of my platter.

I laid the ends of the coil one over the other and make an angular cut through both, to create a joining edge. I set the wheel to spin and work with the foot, centering it and bringing clay down to join it seamlessly to the body of the platter. I work on this a bit, making sure the foot is compressed, centered, and well joined.

Here's a photo of the finished platter (note the cleaned up edge), and a bit of the tile with Amethyst having been painted over the white base.

 The technique has all sorts of possibilities. I encouraged my students to play with it, telling them I'd love to see where they take it and how they make it their own.


Handmade in Israel said...

So interesting. Final piece looks amazing and I really like your stencil! Did it really only take two hours to create from scratch?

april said...

More or less. I had a pattern to work from, so it just involved tracing and then "cutting" with the heat wire.

Good music always makes things move along.