Wednesday, July 8, 2009

Behind the Wheel: Glazing

Sorry it's been so long between posts, but it's been a busy few weeks. The last few posts showed my mom's studio and a few different ways of working with clay. Once a piece is finished on the wheel or pressed into a mold, it has to air dry for at least a few hours, if not overnight. The wet clay is allowed to dry to a leather hard state. At this point, she can choose to carve a pattern like this

carved goldenrod serving bowl

She also trims the base of the piece to give it a clean edge and sharpen the lines. She centers it on the wheel (upside down) and holds it in place with a few pieces of clay. Then she can use a few different tools to trim the edges.

Once dried and trimmed, the piece is ready for the first firing. This stage of "bisque firing" is done at a lower temperature and the result is called bisque ware. This first firing removes all the moisture and gets the piece ready to take glaze.

Here is some of the bisque ware at the studio....

Next, she melts wax and dips the bottom of each piece to coat. This forms a barrier so glaze won't cover the bottom. The glaze would melt and stick to the shelf in the kiln during the next firing, so it's a good idea to keep the bottom clean!

Then it's time for the heavy artillery. She uses this compressor to spray or airbrush glaze onto each piece. There are about a thousand ways to put glaze on bisque ware, but she's quite fond of spraying. We've dipped and sponged and painted, too.

She rests the piece on a bat (kind of like a lazy susan) so she can spin it while spraying.
And then starts spraying...
Glaze is simply a mixture of silica, oxides, and colorants suspended in water. Because bisque ware is so porous, it practically soaks up all water from the glaze and you're left with layers of what feels like chalk on your piece. This is where I think it's safe for me to say it takes a lot of skill to glaze well. It's not like you're seeing the bright, shiny colors that will be on the final product. You have to know exactly how much is enough and what the colors will do when mixed without being able to see them during the spraying process.

Hard to believe this already has at least two coats of glaze on it....I wasn't kidding when I said bisque ware soaks up glaze like a sponge!

Heavier pieces will "stay put" while sprayed, but jewelry tends to be so light, she has to carefully hold them in place while spraying : )
You can also layer glazes on top of each other and create new combinations. Below is a picture of some rings glazed in black (on top) and black mixed with gunmetal (on bottom). The black ones are easy to see the dark color glaze in its "powdery" form, but the bottom ones with gunmetal layered over the black are a little trickier. Most glazes look more like whitewash on the porous clay, so it's all about knowing what works and learning how much glaze to layer.

Here are a few other bisque ware pieces with glaze from the studio. Here you can see some of the darker colors stand out, but most of it is just pale whitewash. I keep pointing this out because I was shocked the first time I saw this process. It's just amazing to me how much you have to do by feel and with practice.

Once glazed, the pieces are ready for the second and final firing. This time at a much higher temperature (about 2000 degrees). The glaze firing step is rewarding and challenging. Sometimes a piece comes out cloudy or the detail of the carving is obscured because you put on too much glaze. Other times it's washed out because it wasn't enough glaze. Sometimes the color combinations look muddy rather than blended. Sometimes glaze can "jump" from one piece to another if they are sitting too close get the idea. This final step is the most rewarding, but also quite challenging!

The two pieces shown as examples (the small bowl and trivet) are now finished pieces and will be in the shop soon. I will do a before and after post just to show the striking difference once I take pictures of them!

And the rings are all but gone...
The two black ones sold already...

But this gunmetal one will be in the shop soon...

And the other gunmetal ring?!?! A certain potter may or may not be wearing her first ever piece of fashion jewelry. So proud!

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