Cone 03 Glaze Results | Slipware Glaze Results | Glaze and Clay Body Tests | Back to Earth Pottery

Testing various clay bodies and slip at cone 03. Pots were bisqued to cone 06. Most pots in this kiln were glazed with Pete Pinnell Clear, some with added colorants to create translucent glazes that are tinted. Most pots slipped with Jason Bige Burnett slip. Recipe in this book: www.amazon.com...

[@pottersjournal]

That is some serious clay, glaze and slip testing, an entire kiln load. Nice test tiles with trees, cactus and more. Do you sell your testers, janicethepotter laughed at me but I did manage to get a few, yours would make a nice addition.
My white slipware, I've never mixed a proper white slip from a recipe. Started by using an O4 casting slip, that was just sitting here on, O6 stoneware but was occasionally coming up with problems. Switched to an O6 white clay, randomly picked, mixed from powdered form and all has been OK. Van Gilder did the same but probably and educated choice by what was in the body.
Again, great imagery.

[@BacktoEarthPottery]

Thanks!
Unfortunately I don't have another kiln. I have really wondered if a test kiln would be a good investment. I have no choice but to fire an entire kiln load. I try to fire some pieces that will most likely work, like the white fritware that I have tested already.
I was wondering about using a low fire casting slip. I guess I thought that low fire white clay is always porous now matter how high the firing is, so it would be weak at best. Maybe that isn't true??? I'm surprised it works on stoneware. I use a porcelain slip for stoneware and that works without issues. Making slip from a recipe seems easy enough, but has turned out to be a little bit of a nightmare. At this point I don't really think I would be confident that the slip would hold up over time even if it looked to be successful. Low fire is very difficult. I think the materials that we have now must be different enough that it doesn't work as easily as it appears to have been... I'm not really sure. I've fired a lot of ugly pots over the past few months 🤣
Haven't considered selling my testers... but whatever it takes to make up for the all the testing 🙃

[@micheledickey4066]

Okay so let me try to help you. If you want to make functional ware such as mugs plates bowls or things that are going to hold food or liquid please use stoneware clay. Also if you don’t want to glaze the bottoms this is a must and I totally agree that it cheapens the look. If you fire your clay to the top temperature and then try to apply a glaze it the pot is already vitrified, that’s why it’s hard to get the glaze to stick. You may be well aware of what I’m saying but I want to make sure so the rest makes sense. I’m not sure why you are firing your bisque and glaze backwards but these are kindof hard rules to stick by. Definitely be sure to get a broader range of witness cones especially when you’re testing. That would really help to narrow things down. First try and choose a clay that you like and then go from there with the glazes. Or the other way around. Find a clay that vitrifies to less than 2% to make sure your pots are able to be used for dinnerware and vases etc. I feel like you are going around in circles with all of these clays and glazes. May I suggest you NOT buy a test kiln! There is so much wrong with having a test kiln. For one even if the kilns are exactly alike and the same brand the size makes a BIG difference. A smaller kiln will heat up much faster and cool much faster. The elements in each kiln are going to be different as well. You get totally different results with test kilns. Also one thing I noticed is that you have flat things on shelves with tall things. Try and pack your kiln more evenly. To get the most out of the room in your kiln put the pots in by height. So if you have a bunch of flat pieces put those on one shelf, making sure that at least 2 elements are showing on that shelf. Put your 3” piece on the same shelf etc. Of course you can use half shelves. If you stagger the shelves you may get more even heat through the kiln. To get more durable clay got and sand will reallly help!! Most terra cotta clays do not vitrify at all. I’m still watching and trying to comment as you go. There are several places you can buy clay from in much smaller quantities. I’ll try and make a list for you. I absolutely love your decorations and your carving. Be sure to test the slip for viscosity. It looks like the piece at the end that was chopping off don’t fit eachother. Usually that causes crazing but if it’s really bad it can shiver. My feeling here is that if you don’t like something about one of the clays just stop using it, I know you spent a lot of money on it but continuing to invest time energy and other materials on them is such a waste. I really hope this was at least somewhat helpful. I’ve been making pottery for almost 30 years, and much of it well before the internet so testing was the only way to learn. I hope you can narrow things down so you can come to a conclusion and start testing with the things you know you like. Best of luck to you.

[@BacktoEarthPottery]

@@micheledickey4066 Thanks for the reply. I have been making stoneware pots for 13 years. I'm experimenting with low fire, more or less for my own "fun". I'm not able to pack the kiln efficiently due to the fact that I make stoneware mostly and to fire a entire load for a cone 03 glaze is still experimental at this point. So, I don't have the variety of low fire ware yet. I'm hoping to be able to fire to cone 1 eventually. It is possible to make functional pots with terracotta as some clay bodies will vitrify similarly to stoneware when fired high enough. I do realize they can become brittle too though. Another option is using terra sigillata on the bottoms. It isn't impermeable, but it helps to lower the absorption rate. I'm not really looking to make functional pots in low fire, but I do include some in each firing during the experimenting process to test the durability. I have tested some at cone 04 with EM 106 clay. They have held up as good as stoneware and the feet are not glazed. It really depends on the clay body. I have heard that about test kilns, but it would be more efficient to test clay bodies and glazes just to get an idea. I have seen low fire potters bisque low and glaze higher. It works ok for thrown pots, but hand built pots can warp. I have found that the glaze I make works fine. Commercial glazes seem to have an issue with off gassing and can come out cratered, but I had the same thing happen when I bisqued to cone 03 and glazed to cone 06. It seems like most low fire glazes are mostly just for low fire white clay bodies, with a few exceptions. Bisquing high and glazing low can be done by floucculating the glaze (dippable). I have tried that with EM 106, but that clay body seems to be quite vitreous at cone 04. I have not tested the absorption rate, mainly because it is a clay that warps too much and I don't plan on using it. It does have a lot of potential though. Inevitably I will be making mostly nonfunctional pots in low fire... that is the goal. I will have some Earthen Red clay (Highwater) in the next firing. I have used that in the stoneware range for years. There's been a lot of changes in raw materials over the past few years and it has really affected low fire claybodies and glazes. I think it is much more difficult now than it used to be as a result. The issue with slip is one of the most difficult parts of it. Just glazing alone is fine and I have had very few issues with that. I have made two new slips to try from clay bodies as opposed from raw ingredients. I'm using a stoneware body and a raku body. I am trying to match the shrinkage rate of the commercial clay bodies. I won't keep making slipware if it doesn't work. That is mostly where all the testing and experimenting has been. It would be great to make my own clay with frit in it to make a very durable and vitrified clay body for low fire, but it's not that practical without a clay mixer and pug mill. Thanks for the help!