This is one way I make slab plates. I posted the pictures to FB but am reposting here with descriptions of each step. You can adjust the steps if your clay is more or less forgiving than mine.
First cut slabs and let them rest overnight to stiffen up some. These slabs are 10mm thick.
Trim the slab with an undercut bevel, and save the trimmed edges.
Sprinkle something on your form to prevent the clay from sticking. I use corn starch.
Place the trimmed slab bevel side down on your form and paddle it THOROUGHLY, from center to edge, then once more evenly all over. You can use whatever you want as a paddle, here I used a sandbag, but I usually use a wooden paddle.
Place the trimmed edges you saved back on the paddled slab, followed by a paper towel or other cloth, and your board. Turn over the form to release the slab onto the board.
Press the center of the slab down gently and let the edge pieces support the edge of the plate. While supporting the edge with one hand, use the other to define a concavity in the bevel with a convex tool. Anything convex and with a curve you like will work. I used a little ball here. Sometimes I use a rib, sometimes a roller, sometimes a clamshell. I like rollers and balls because they compress the edge well.
Finish and further compress the edge with a damp (not wet) chamois or sponge. Done!
This firing of the kiln went too long, resulting in Orton cone 11 flat. Ideally, it would be cone 11 touching, then sagging a bit.
Upon unloading the kiln this morning, one thing was immediately apparent: the right side was far more reduced than the left. Yellower glazes and more slumping. Even on the left side there was some slumping, because of the excessive temp., and because of the clay which contained some low temp high iron clay to help seal the ware against leakage.
Chosen Karatsu came out pretty good, but the white was on too heavy, running down the pots too much. It still came out looking ok because of the clay.
Most of the teabowls warped or sagged, so I only get to keep 2 or 3 of the 15. This is why teabowls are expensive, kids…
All in all, not a bad firing, but need to adjust clay bodies, and pay closer attention to cones. Also, figure out the over reduction on the right side. It might be that one burner that sounds a bit off.
I’ve gotten pretty far behind keeping up with the blog, falling into the bad habit of making small posts to Facebook. One of my areas of increased effort over the next year will be to work more on maintaining the blog, and getting it more integrated with other forms of social media. Trying to keep track of them all is like trying to herd cats.
I had made one promise to show before/after pictures for a couple of pieces, the first of which is the slab/paddle built sake chiller w/ feet and lugs:
The other thing I’ve been working on since early this year is getting a usable kohiki/clear glaze combination, because for some reason a lot of customers have been requesting white work. They have also been requesting black, so I’ve been working on getting a reliable semi matte black glaze. Mission not quite accomplished, but I feel I’m most of the way there. Here is the kohiki I’ve come up with and I am happy with it:
Here are some of the pieces with the new black glaze. It seems to look best thin, and as with most glazes looks nicer over interesting wild clays rather than processed clays.
….is without a doubt the Peter Pugger de-airing pugger/mixer. Until two years ago I did all of my clay and stone mixing in a large deep platter by hand, and it was killing my wrists. Hearing all the wonderful things Peter Pugger had to say on their website, I took the plunge and decided to spend the money and save my hands. I figured if the thing worked half as well as it was supposed to, I would be ok.
Well, it is now about 2 years since I got it and it does everything it is reputed to do, and does it very well. My wrists are now pain free, and I have saved hundreds of hours of time processing and blending clay bodies.
Blending wet clay bodies usually takes about 15 minutes of mixing, but mostly I mix dry materials with water (sometimes blending into wet bodies), and this takes a while longer, usually around 30 minutes.
In my work, keeping the character of the wild clay is of utmost importance, and I’ve found that de-airing generally kills that character dead. However, the de-airing is necessary in getting the water to penetrate the dry materials more quickly, so that I don’t have to let the pugged clay sit for a month before using.
My solution to this is to let the clay mix, then I de-air it once completely, followed by re-mixing the batch for 5 – 10 minutes after reintroducing air. This gives me clay that is not as easy to throw, but which gives very nice trimmed texture.
Here are some pictures of some clay from the other day which I collected from the mountain behind my home. I added the dry/damp clumps of clay to the hopper (removing as many large rocks as I could find), then water, then mixed. I repeated these three steps until the hopper was full, then mixed for about 20 minutes, turned on the vacuum pump, and de-aired completely.
Next I went to lunch. It was yummy. It was sunny on the deck and there was a cool breeze. The neighbors have a great cherry tree in full bloom and the wind was blowing the petals off, and they were fluttering across the yard like giant pink snowflakes. I noticed as I saw some of them fall across the deck that the wisteria was budding out and even starting to show some purple. Nice. I imagine the wisteria will be in full bloom a few weeks early this year.
After coming back to the studio, I re-introduced air to the mixing chamber and mixed some more, then pugged it all out and made some pots. The whole process took about 2 hours. It takes even less time if you decide not to include lunch, but I recommend including it.
Getting ready to set up a whole kiln load of glaze tests to fix my misbehaving ame (iron/ash) glaze, and realize that I’m out one very important ingredient, red ochre collected from a place right here in Taku. Completely forgot that I had used the last of it in my last glaze batch mixed up a couple months ago. Doh!
So…. Delay the mixing of test glazes for tiles and cups, I had to spend the day crushing and sieving red ochre. I haven’t used my man powered stamp mill in a while, and I added too much material to the mortar. My wooden pestle (4 foot long pole) that I use to stamp the material was just not up to the task because it was too light to sink down into the material and get it circulating in the mortar. To remedy this, I retrofitted one of my wooden pestles with some 3cm diameter round steel bar left over from a long piece of bar I cut into sections for my kiln’s grate bars.
This new pestle worked really great, so great in fact, that material was flying out of the mortar from the striking force. So I proceeded to cut down a large cardboard box to keep most of that stuff from flying out or away. It is really hard work digging it, carting it around, and crushing it, I hate to lose any at all.
So anyway, here are some pictures of today’s festivities, and I did wear a dust mask, so I don’t have to worry about getting red lungs…
Lately I’ve been working on ways to bring out the crackle in my teabowls, as well as make the crackle finer (without having to use them for decades or centuries, or reformulate my glazes, so in other words: cheat).
These two bowls had big crackle ( 1cm +-) and I reheated them, then doused in cold water.
***WARNING: Ceramics generally don’t like to be heated or cooled quickly. Don’t do this if you’re going to be upset about breaking a bowl!***
For the kohiki bowl, I heated and doused once to make the crackle smaller, then reheated to open the crackle wider, and closed the damper on my stove, to get that carbon to penetrate the crackle.
Because the body and the glaze were vitrified, but the white slip in between wasn’t, spots (where the slip was thickest) on the rim separated from the body and had to be restored with lacquer and gold (*1)
The results vary, and it is high risk, but you can get an idea about how your bowl may mature over years of use, and plus it’s just fun to play around with fire…
Another common way to bring out the crackle in you ware is to boil it in a pot of strong tea for a few minutes. The tannins will then turn brown, especially if you put the piece out in the sun to dry (or any other UV light). For an even darker, quicker reaction, after the piece is dry, apply some iron acetate. The iron acetate reacts with the tannins and turns quite black over a period of 24 to 48 hours. This is actually an old woodworking technique that I applied to pottery, and it works well, in addition to being non toxic.
***Results may vary***
(*1: I didn’t use real gold for this bowl, but I would on a very nice piece. For this piece I used a brass based metal powder. For more info on this kind of repair, check out Dave Pike’s blog, or store on Etsy)