Yesterday I read an interesting article on how to think like Leonardo da Vinci. It really resonated with me and got me thinking about how I could apply it to my pottery.
I read a post over on Deborah Woods’ blog about throwing in cold weather and it got me wondering….
She said she uses a crock pot in cold weather to keep her throwing water warm so her hands don’t freeze, which I actually think is kinda brilliant.
Are there any others out there that use warm/hot water in cold weather? I guess whats bothering me is that I’ve actually tried it a few times, sometimes by accident, pushing the lever more toward warm, sometimes on purpose when it was cold. It took me a while to put it together, but I seemed to have a lot of trouble throwing with warm water. When I mentioned it to a more experienced potter, they said ‘Oh, yeah, you don’t want to throw with warm water, always use cold.’
For you warm water throwers, do you have challenges? Or is it something I’d eventually adjust to? I’d also imagine it’s probably dependent on the clay body.
I’ve got to get back into the studio soon…. WAY too much time to think lately…..
So where am I headed from here?
Being on injured reserve these days, I have plenty of time to think.
What my experiments have shown me is that I definitely want to explore this direction further, maybe take it somewhere no one else has. I’ve already had some happy accidents with streaking, I’m wondering what else is waiting out there.
For starters, I want to go ahead now and get some proper equipment and materials and see if I can make an even better terra sig using Vince Pitelka’s instructions.
I’ve been using sig on my saggar pieces, and I really like them that way. I’d also like to try it on raked raku, although I’ve heard mixed results of getting the resist slip to adhere properly to a smoothly burnished pot.
The high shine of low-fired sig is lost when the pot is fired up to stoneware temps, but I want to experiment with that anyway. The more satin finish might be just what I’m looking for.
In part 1, I talked a little about proportions of clay and water and basic clay prep.
Deflocculants will definitely improve your results over mixing only clay and water. What they do is help separate all the individual clay particles and keep the smaller particles of clay suspended until the larger particles settle out. What to use is a whole other matter.
By far, the most recommended deflocculant for terra sig is sodium silicate. It’s very effective, and only a few drops are needed. Other choices include soda ash and tri-sodium phosphate (TSP).
For my first experiments, I used TSP since it was readily available at the local building store as a cleaning agent. Make sure you get actual TSP, and not TSP substitute. I used about a teaspoonful in a gallon or so of slip and it was plenty. Later I used about a tablespoonful in a 3 gallon batch of red sig slip.
So then you mix well – I used a paint mixer attachment on an electric drill for a few minutes.
Depending on the clay you’ll usually see an almost oily appearance to the surface when you stop stirring from the fine clay on top of the water.
Then walk away. Let it sit. 24 hours minimum. My first try didn’t sem to be separating into distinct layers, so I let it sit for 3 days.
You’ll either get layers or not, but either way you’ll then want to carefuly siphon off either the top 2 layers, leaving the heavy third layer behind, or siphon off the top 1/2 to 2/3 of the liquid if there isn’t distinct layering. This is the terra sig you’ve been after.
You’ll need to experiment with the consistancy. As I said earlier, my first batch used WAY too much water, so I had to evaporate some of the water away to get a usable product. I actually poured it into an old bisque bowl I had laying around which let it evaporate and also absorbed and wicked away water through the bowl.
Next time – Future testing
I’ve been looking at all my various notes on all the variations of terra sig. I thought I could put it all together and maybe make sense of it all.
Up to this point, I’ve just been trying to see what kind of results I could get without a whole lot of trouble, gram scales, deflocculants, and measuring specific gravities. I think I did pretty well, I even surprised myself a bit on my first tries I suppose. But comparing notes, and sitting down and doing a bit of calculation and comparison, I probably could have done a bit better.
This first time, I used about 2 pounds of dry clay to a gallon of water. From what I’m looking at, that’s probably way too much water to start. It made the slip easier to mix, but was probably overkill and all that water has to be evaporated back off. The trend I’m seeing is something more like a little less than 1 cup water for every 100 g dry clay. What I used was 16 cups to 1000 g, it should have been about 10 c.
And do yourself a favor, use dry clay, it will mix a lot easier. I busted up some scrap throwing clay in a heavy bag with a big hammer. Don’t do it in the open, because 1) you REALLY don’t want to breath that fine dust, and 2) that fine dust is actually what you’re after, so don’t waste it.
If your clay is still moist, just use a sur-form tool or cheese grater and shred it into a bucket and let it dry. Then add it slowly, a little at a time, to the water, then let it sit for 20-30 minutes or so. then use the power tool of your choice to give it a good mix. I used a paint mixer attachment on a drill.
After going over the test results of the experimental pieces I did at the last saggar fire, I learned a few things. Some are probably obvious to those more experienced than I.
For any color at all besides black, some kind of metal salts/oxides are required. I probably should have realized this, but I was hoping perhaps some of the trace minerals in certain organics would be strong enough on their own, trapped under the aluminum foil. They weren’t. Their main function seems to be to influence the colors/shades of any major metals already present. Ferric chloride, copper carbonate, and copper sulfate are all good starting points.
Pieces of broken off pinecones give a nice dark black. If you want good blacks, pinecones and needles are a good bet. It also doesn’t take much, start conservative.
Brushing on ferric chloride works just as well as spraying. And it’s a LOT safer, in my opinion. Airborne ferric chloride is just bad news. You still want to wear plastic gloves and be very careful. It’ll also ruin your brush, so use a cheap one, foam works well. I want to experiment with building up varied layers of diluted FeCl in the future.
Tinfoil saggars are the way to go, in my opinion. Comparing with other work from clay saggars, and pit firings where some was wrapped in foil the same way and some not, the colors just seem to come out more intense. You can also achieve good results with much less raw material since you don’t have to fill the space between the saggar and the pot. That’s just my personal taste. Some people like more delicate, muted coloration and that’s cool too. And despite reading in several places warning about not firing past the melting point of aluminum (1100F), I’ve never seen or heard of a problem with it. The aluminum foil doesn’t melt, it simply burns away. I think the regular weight stuff works fine, but experiment with some heavy duty and see what you like.
Terra Sig takes the color just as well as burnished or unburnished clay. I thought that maybe since it is a tightly packed surface of smaller platelets it would be less permeable to the smoke and fumes, but it didn’t seem to be a problem. Your clay, however can make a big difference. Earthenware bisqued to cone 06 is much less permeable than a mid/high fire stoneware bisqued to cone 06. The colors are still very nice, but are lighter and more delicate. Again, lots of room to experiment.
More detailed instruction is available in Alternative Kilns and Firing Techniques by Watkins and Wandless. It’s chock full of ideas, many of which can be mixed and matched between the different techniques. This one will really get your imagination flowing.
For more posts about saggar firing, click on the SAGGAR tag below.
Deborah Woods had a good idea regarding my recent clay challenges, thinking it could be the clay hadn’t aged sufficiently yet.
I hadn’t considered the aging factor. But now that I think of it, it could be contributing to the problem. The clay I got was ‘fresh off the truck’, so it hasn’t really aged. However, so is the white stoneware I’ve been using, as well as all the other clay available at the center, so there’s some sort of baseline usability there that the buff clay doesn’t seem to have.
The instructor that used that clay also had multiple bags in various states of age, with trimmings and reclaim constantly being wedged in, so that probably improved things a lot. And as I mentioned, he throws very dry. The first thing I think I’m going to try is cutting way back on the water.
For me, an idea clay would be serviceable ‘off the truck’ and any improvement with age would be a bonus… That probably isn’t very realistic, and it make sense to age your clay, I’m just not in a situation where I can age clay right now.
I’m having a much more difficult time adjusting to the ‘old’ clay I used to throw with than I thought I would. Even though it’s supposed to be good for beginners to learn with, I’m finding it a lot more finicky than I remember. It’s soft, yet stiff at the same time. And STICKY. It doesn’t want to move when doing a pull, instead preferring to carve off in my fingers and on my sponge. And yet, I somehow keep putting thin spots in the wall at random, which later either collapse or tear. aaaaaaaahhhhhhhhhh!!!
I did manage some small 1.5# bowls Tuesday, but the misbehavior seems magnified on larger amounts. I tried a 4# vase tonight which took an hour of finessing to get into shape. Then it collapsed when I put the plastic over it to dry. And then there was a good pound at least in the bottom of my slop bucket when I cleaned up. — not happy.
Not giving up, but definitely frustrated. I’m going back to small bowls and mugs until I get a handle on this sticky stuff. I remember my begining wheel instructor throwing VERY dry with this clay. I’m thinking that’s the only way to battle the stickyness.
About 2 years ago I made the decision to concentrate my efforts on learning to throw the white stoneware clay as well as I could. Until then, I’d been switching between 3 or 4 different clays, all with drastically different feels, and I felt I was not making much progress with my skills.
I’m still no expert with white stoneware, but I do know my skills have improved farther and faster than they would have had I kept changing clay bodies every time I threw.
So now with the saggar firing behind me, I’m considering a change. I’ve had some requests for bowls, and I’m thinking I might give some functional glazed ware another try for a change. I just used up the last of my white, divided it up into 3 1# balls and did some quick pieces. It was fun to throw some quick one-pounders.
To get the requested glaze colors, I’ll need to change back to the grogged, buff stoneware we have at Pullen. It’ll be a fun change, but I’ll be back to white stoneware soon. I can’t help myself.