Kelly in AK

You got that right!

I’ve been using local clay for about five years, digging and mixing it. So no one gets the wrong impression, I’m not a production potter, this is a labor of love. It’s my night job and I don’t make money at it. Just enough to support my habit. I have put thought into making the process as efficient as possible though. I’m fortunate that tons of clay are available every time a new house gets built in my neighborhood. I just drive up, load up, and go. That’s step one, get the truck as close as possible to the clay. Most everything happens in my driveway (I’m not sure what the neighbors think, haha!). I dry it, crush it, then mix with water to slip using a big drill and a mud mixer bit. Then it’s sieved to 60 mesh and I let it settle for a week or two and siphon off the excess water. After that I add some Veegum (mix this up a day ahead) and pour it into drying trays. Those are made from 2 x 6 lumber with 1/4” mesh attached to the bottom and lined with fabric. I have three and they stack. After a month or two it’s ready to wedge. It doesn’t dry perfectly even, the edges are stiffer than the middle and so I stir it around once a week or so. Wedging is the biggest chore. I’m looking forward to buying a pug mill, been saving up for it. I may buy a pump to move the slip some day too. I mix around 300-400 pounds a year. Adding up the time, it takes a few days work.

I know for certain that different clay bodies shed their water at different rates. The most remarkable I’ve experienced was a body made of two parts OM4 and one part pumice (it was pumice I dug up from a deposit in Utah). I regularly fired it from greenware in a raku kiln in less than three hours. It was pretty awful as a clay body, even with all that ball clay it still wasn’t plastic and never got very strong. It melted around cone 1. Never blew up though. The large scale industrial producers definitely have their process fine tuned. I got to tour a tile factory in Pennsylvania once, it was enlightening. Their clay body had a very high percentage of non plastic material, just enough clay to hold it together. It also had an exact percentage of water and was used in powder form. A measured amount of powder was dropped into a steel mold, pressed hydraulically, then popped out as a tile. From there it was on a conveyer under a glaze sprayer then into a tunnel kiln. Nothing ever stopped moving. 180° is a good temperature to candle at, you’ve just got to do it long enough to get the water out. Digital kiln controllers make this easier than it’s ever been in the history of ceramics. We live in good times.

Strongly agree with Bill’s post. Older elements take longer to heat than new ones, but then again a small kiln is less to heat. You’ll have to discover how long it takes your particular kiln to heat up. Definitely check to see if you can see a cone through that peep. By arranging the distance and height of the cone(s) you may be able to see it, or even part of it, through a small hole. No matter what you need some cones in there to check that the pyrometer is accurate. I had a similar kiln, tiny, three switches, low medium and high. I dried things out with the lid propped 1/2” and one switch on low for several hours. If it heats too much too fast, turn off the switch and shut the lid a couple hours then repeat. 210° F is the magical place things begin to explode. My experience is 180° for 6-8 hours keeps things from blowing up. It may be helpful to be familiar with the color to expect at various temperatures too.

You need: Proper orifice sizes for lpg and proper regulator for lpg.. Natural gas is “big” and low pressure, needs a big orifice and big pipes to deliver. Putting lpg through that must have been interesting. LPG is concentrated and has loads of pressure. Smaller orifice, more pressure, narrower pipes. Vince Pitelka has an orifice chart on his website. Ward burner is a font of wisdom in this department.

Seattle Pottery Supply says they have some talc as well. Now, this next bit is information not advice, because I’ve never made kiln shelves and don’t personally know anyone who has. Alumina and zircopax are both highly refractory, much more than talc. My experience (only to cone 6, mind you) is that zircopax sinters together significantly harder than alumina. My opinion is that I would rather chop existing kiln shelves into the shapes I need or buy them than to try and make them. That is, I suppose, because I now have more shelves than I need, and a day job. When I had no money, lots of time and lots of clay, making my own bricks to build a kiln worked out just fine. That was against the opinion of people more knowledgeable and experienced. People can have different opinions and both be right. As for advice I would say first to check if Michael Cardew had anything to say about making kiln shelves in his book “Pioneer Pottery.” You can take anything in there to the bank. Next, find a video of Isaac Button loading his kiln. He made his own shelves. Finally, take a look at Tony Hansen’s Digitalfire website. He’s made his own shelves too. Please let us know how things work out, I’d like to think we’re learning and teaching together here.