Archive | October, 2008

Pottery Pigs

28 Oct

I just finished teaching three separate 6-week pottery classes. One of our favorite projects was these Piggy Banks:

The kids did a spectacular job . . . don’t you think? And some of them were very young. The boring one with the “normal” eyes is mine. I was going to teach the kids to do eyes like that, but they got way out ahead of me, and I’m so glad they did! They required a lot of help inputting the bodies together, but they figured out on their own how to do the embellishments such as eyes and noses and tails. The pigs’ legs are coil-built and were added to the bodies along with the eyes and such.

To make these pigs, I had the kids pound thick clay slabs over some bisqued bowls I had made earlier. (I had trimmed the bottoms of the bisqued bowls round so that they could be used either as slump or hump molds.)

They each made two bowls.  We hardened the clay in our little cheapie microwave oven for one minute at a time, a total of two minutes per piece, with a waiting period between hardening sessions. The first time in the microwave, you can leave the clay on the bisqued bowl, but you should take it off the bisqued bowl the second time, or it might shrink too much and crack.

Once both bowls are hardened, you can scratch and slip and join the two pieces to make one hollow form. This is where the kids needed the most help. It’s a tricky operation, especially for little hands. Adding the features is the fun part. Mostly, we did that at a second session (our classes are an hour and a half). When the pigs’ bodies have set for a week, even wrapped in plastic, they will be stiffened up a little and a lot easier to work with.

Be sure that any hollow enclosed spaces (such as the pig’s nose) have a hole in them. Nostrils are a good place for this. Also, if your kids use any thick pieces of clay, poke some air channels in them with a needle tool to allow moisture to easily exit the piece. I try to do this in a spot that won’t be visible, but really, these tiny holes seldom show through the glaze.

The piggy banks have a slot in the top for coins and a hole in the bottom to let kids get their money out. You won’t want to break these pigs! You can get stoppers at most ceramic suppliers. For cone six stoneware, the total shrinkage of the clay will be usually around 12-13%, but ask your clay supplier. You need to know for sure. Measure the circumference of your stoppers (make sure they’re large enough to let quarters fall out) and add 12-13% or whatever your clay shrinkage percentage is, then make a hole that size. Don’t make it too big–if it’s a wee bit small, that’s okay because the stoppers have some give to them. I gave the kids a patern to cut around.

When you make the slot in the top of the pigs, be sure to allow for shrinkage there, too, and make it wide enough as well as long enough.

Oh, and when figuring out how big to make the coin holes, you need to keep in mind one more thing. Cone 6 clay has accomplished half of its shrinkage when it has reached firm leather hard stage. Therefore, if you have allowed your banks to reach leather-hard stage before cutting the holes, you need to add half the shrinkage percentage instead of the total shrinkage. So if your supplier tells you that your clay will shrink 12.5%, and your clay has reached firm leather hard stage, it has already shrunk 6.25% (or thereabouts).

If you find that some of your kids have cut their holes a little large, you can get a larger stopper or a tapered stopper like a natural cork. If you’d rather not do that, you can add a bead of silicone around your stopper’s rim, and smooth it to a taper and let it dry. This will most likely be sufficient to fix any loose stoppers.

This isn’t my usual detailed tutorial, and if you have questions that I haven’t addressed here or covered in an earlier post, feel free to ask. I had really intended to only publish the photographs, but this is such a fun project, I thought you might want a few more details.

God bless,


Glaze Firing Pottery

14 Oct

You’ve got your pottery all covered in promise–that is to say, glaze. The glaze will either make or break your piece, so be sure to follow my suggestions in the post on glazing as well as reading and following any instructions that might have come with the glaze, stack your kiln carefully (nothing touching anything else, no glaze touching shelves or walls), pray, and stay within reasonable proximity to the kiln.

We’re talking about electric firing here, btw. Choose a day in which you don’t expect the power to go out. That might sound obvious, but starting your glaze kiln on a dark and stormy day could have unfortunate complications. First, the barometric pressure does make a difference in the outcome of your firing. Second, if you’re using a computer controller, lightning is not your friend. You’ll be biting your nails until you’re able to turn both the kiln and its breaker off (or pull the disconnect switch). Third, even if the power just peacefully dies without a surge, it’s better not to interrupt a firing. Doing this can have permanent consequences to your wares–sometimes good, more often bad.

Read my precautions about kiln venting given in my post on bisque firing. In fact, read the whole post again. There’s a lot of stuff there that applies equally to glaze firing. Directions for firing differ from kilns controlled by a sitter to kilns controlled by a computer device and its requisite pyrometer. (If you don’t know what I’m talking about, read the bisque firing post.) I’m going to put the instructions for the sitter in black and those for the computer controller in italic.

One caveat: make sure your glazed ware is dry. If you think your ware may have residual moisture left over from glazing, start your firing on low power for an hour or so.

  • I often start a glaze kiln on high power and leave it there for the whole firing, but the sitter kiln I use is at the art & science center where I teach, and I’ve made it a point not to have any sensitive glazes there. If you have glazes that need a soak at the peak temperature, you might want to turn down one or two of the elements when the firing is nearly done. You’ll know this from your past records and from the behavior of the cone packs you have placed in the kiln.
  • Some people do recommend a slower start, even for a glaze kiln, but I typically start my kiln out at full power–that is, I tell it to heat at 500 degrees Fahrenheit per hour. It will be able to do this at first, but soon it will have to slow down because it can’t deliver enough power to rise that fast. The speed at which your kiln is able to heat depends on the elements, power available to them, size of the kiln, ambient temperature, and probably the phase of the moon.
  • If you’d like to soak your sitter kiln, wait until the target cone (in my case, 5 or 6) just begins to bend, then turn one or more elements down to medium. Leave them like this for the duration of your desired soak (usually about 30 minutes or less), then, if necessary, turn them up again. Ideally, you shouldn’t have to turn them up. You should learn, by experimentation, to turn the elements down just enough so that you will slow the rise of the kiln, but not stop it.
  • If you don’t yet know what temperature will cause your target cone to bend, you’ll need to watch the shelf cones closely as the kiln approaches peak temperature. A thermocouple may read 2260 degrees F. and yet the cone 6 on your shelf may show that the firing has achieved cone 6 temperature/heat work. Set the controller to slow your firing down when it reaches about 50 degrees below your target temperature. I tell it to fire at 50 degrees an hour at this point. Then, if you like, you can also program a soak at peak temperature of 15-30 minutes. You don’t want to soak too long, or your glazes will be in danger of running off onto the kiln shelves, even if you haven’t overfired them. At these temperatures, they will have become a viscous liquid, like molasses or honey, and too much time allows them to flow into places you’d rather not have them go.
  • For all practical purposes, you are done firing if you’re using a sitter kiln. Leave the vents turned on and keep an eye on things until the kiln has cooled enough not to present a danger of fire, then just allow it to cool naturally. When it is no longer warm to the touch, you can check to see if it has cooled enough to unload. Ideally, you should wait until ware and kiln furniture can be held in the bare hands for any length of time without discomfort from heat. Once you’ve been doing pottery for a while, you can think about turning the kiln back on at around 1900 degrees and thus slowing down the cooling to encourage microcrystaline matte glazes, but that’s a very advanced technique without a computer to help you and requires knowledge you can only gain from experience.
  • If your glazes are all glossy ones, you, too, can just turn the kiln off and let it cool at this point. If you have microcrystalline matte glazes in the kiln, set it to fire down. It should be allowed to cool naturally (just program in a high number–say 500) until it reaches 1900 degrees. You should then have it cool at 100-200 degrees an hour until it reaches 1700 degrees. At this point, you can allow the kiln to cool naturally. Just don’t program another ramp, and it will end the firing. As above noted, it is best to allow the kiln to cool until ware can be easily and comfortably be handled with bare hands. You’ll have to learn by experimentation how fast to cool the kiln during the 1900-1700 phase, and it will likely differ from glaze to glaze. A longer cooling makes a more matte glaze, but you can cool so slowly that normally buttery mattes will become almost dry, and that may or may not be what you were after.

A quick word about unloading a hot kiln. I confess that I have unloaded kilns that were so hot they made my welding gloves smoke and I had to take them off and let them cool before I could continue. This is considered bad practice, but after being patient for about so long, it’s sometimes more than I can do to be patient for another six hours or so. So . . . if you choose to ignore my good advice (as I sometimes do) . . .

  • Be sure to set your hot pottery on a suitable surface–like the lid of another kiln or a fire brick or a fairly warm kiln shelf.
  • Remember that thermal shock (sudden change of temperature) is the mortal enemy of pottery and glassware. Do not allow your pottery to contact a cold surface. If you have a history of Raku, know that raku clay is especially formulated to withstand thermal shock, and it sometimes breaks anyway.
  • Do not remove pieces with large flat bottoms from the kiln–plates, platters, etc.–because they will break. They’ll crack right in two. I promise.
  • Do not set hot kiln furniture (or hot pottery) on a vulnerable or a cold surface.
  • Wear protective clothing. The best heat-proof gloves you can afford, long-sleeve, natural fiber shirt, and tie long hair back.
  • Finally, really–don’t do it. You can wait. The pottery isn’t going anywhere.

So, I’m afraid this last bit of advice is like handing a kid a condom and telling him not to have sex, but you’ll make your own decisions about this sort of thing. I did. So, you might as well learn from my mistakes so that you can go on and make new mistakes of your own. 😉

Your pottery is out. Some of it is beautiful; some of it disappointing; and some of it may even (God forbid) be stuck to the shelf. Most of it will need sanding on the bottom so that it won’t scratch your furniture. Just use regular sandpaper from the woodworking section of the hardware store. I like 80 grit, but any coarse grit will work. If you have a power sander of any kind, you can use that, but be careful and follow appropriate precautions given by the manufacturer of the tool.

If you have glaze drips on your pottery or on your kiln shelves and furniture, you can use an angle grinder with a masonry disk to clean them off. Again: thick leather gloves, goggles, long sleeves, tie back your hair, use ear plugs, dust mask. Really! Especially the goggles and the gloves and the hair tie.

Making pottery well requires a long and patient learning process (or at the very least, a helpful teacher/mentor.) I know all of this sounds complicated, but it’s no more so than any other skill and a lot less than many. It’s a lot easier than building a house, for example. Enjoy the process; don’t get too attached to any individual piece; remember it’s just mud and you can make another one. 🙂

God bless,


Pottery Photos II

5 Oct
I’ve been doing a lot of talking lately about technical stuff. My next post will be on conducting the final glaze firing using an electric kiln, but I thought you might like to see a few photos of finished pottery for a change–get an idea of what you can expect from that glaze kiln (if it turns out well). If you click on the photos, they’ll either take you to my Etsy site (if the piece is for sale) or to my Flickr site (if it’s not).

This jar was wheel thrown and is intended to hold jewelry or
homemade lotion or such. I painted wax resist on the gallery and the
lid ring and fired the lid in place on the pot. If you fire the lid
separately, it will sometimes warp and not fit the pot after glaze
firing, but if you fire the two together, you have to make absolutely
sure there are no traces of glaze anywhere the two pieces will touch.

I first threw this bowl on the wheel, but I didn’t like it. So I
fiddled with it until it looked like this. I really love it now.
This is not to say you should never give up on a pot, but don’t give
up too easily. You never know what you might make of it.

After the first glaze firing, I didn’t like this fellow’s
shiny skin. Sometimes, if you refire a pot to bisque
temperature (just put it in with a bisque load), it will
give the glaze a chance to “devitrify” or form micro-
crystals, matting the glaze. In this case, I was really
happy with the results.

This vase makes me think of something Snow White
or Briar Rose might use for a bouquet of beautiful
wildflowers–hence the name: Forbidden Forest Vase.

And here are the wildflowers themselves. 🙂 I carved them
into this cup. The dark brown unglazed bottom is colored with
an iron oxide wash–that is, an unspecified quantity of
red iron oxide mixed into a bucket of water. If your pieces
come out too dark, mix in some more water. If they’re not brown
enough, add more red iron oxide (RIO). You want maybe a cup or less
to a gallon of water, and you’ll notice that you need to stir it a lot.
My daughter made this little guy, while she was teaching a bunch
of kids to make them, too. I was teaching wheel, so I was glad to have
her taking care of the kids who couldn’t get on the wheel (we have only
four wheels and in this class there were 8 kids). They all made cute
puppies and kittens, but of course, non as cute as my little girl made.

I made this mask during a class teaching, guess what? Masks! I sort of
thought he looked like Pan, so that’s what I called him.

Well, that’s it for now. I’ll try to get back to you with instructions and tips for the glaze firing sometime next week. Then you’ll be all set to go! 😉

Until then, make lots of pottery!