THE CRAFT OF FIRE

Well, I had a chance to do a firing before the Thanksgiving weekend and grabbed it. The plan was to re-fire the wood ash glaze objects from the previous firing which had been under-fired by about 300° C. Since this time I had to reach 1263° C, it became a great opportunity to test the limits of the kiln, to see how high it could get. 10:15 - start 11:30 - 400° 1:30 - 800° 2:30 - 970° (temp increasing much slower now) 3:30 - 1120° (vent now totally open) 4:15 - 1147° 4:30 - turned off fuel and plugged up the kiln to let the temperature decrease slowly. As you can see, we maxed out at 1147° - and it took an entertaining hour to get those last 27 degrees. Since we were still a ways off from Cone 10, I figured the glaze wasn't going to work. But when I took out the pieces I found to my surprise... ...they have a delightful glossy shine to them. what a difference 300 hundred degrees makes I'm not sure why the one mixed with woo...

Well, I'd been planning to do a firing to test some things out again since April, but it's taken until this weekend to be able to do it. And it was a great firing, with just enough going almost right as well as totally wrong... I fired up a bunch of pieces, including another try at Terra Sigillata , and new experiments with Egyptian paste (using the homemade copper carbonate), and Wood Ash glaze. I sifted the wood ashes through a simple kitchen splatter screen (not sure what mesh it is, although the chunky bits sure got left behind), and didn't bother washing them as some suggest. I then mixed up three different batches... Recipe 1 Wood Ash       38 Feldspar          36 Clay               18 Silica               8 Recipe 2 Wood Ash      50 Feldspar         50 Recipe 3 was Recipe 1 with 2.5% of copper carbonate added, ju...

When working in the Crafts, we talk about developing a certain internal placement or attitude having to do with Permanence , Care , and Tone . In the old Notebooks of School (#8), I found some comments which expanded my reflections on these three points, and I thought I'd translate and post them here. Permanence A plan of work to be carried out should be developed before any activity. This plan should not be altered by other works which may be suggested while carrying out the activity. When other possibilities arise, one can take note and develop them in a future plan of work. Working simultaneously in different activities is fine, but all of that should be foreseen in the plan of work for the day. One should not go on to another production before having finished what one started. Care The workspace, tools and equipment should be ready for use for the work to be done. Tools and materials should be classified and ordered. Tools should be put back in their plac...

We did another firing on the weekend, some raku and some not. This was the firing where I was going to test out my new copper carbonate and get some rudimentary colour on my pieces. It turns out I got more colour on my head than my pieces did. J. checking out the burner It was a sunny 17º outside, warmest March 11 on record, and I actually got a slight sunburn. It's what happens when you're bald and the sun hasn't really shone all winter. I prepared a tin saggar with a bisqued piece inside, with wood shavings at the bottom, a layer of salt in the middle, and then sawdust for the rest, and 8 g of CuCO3 sprinkled throughout - experimenting with a reduction environment, and the copper powder and salt all in one tight space. It came out at 750º, dark grey on the bottom, a heavy black line where the salt met the sawdust, and then black above - and that's it. No copper colouring anywhere. I had also painted a small dish with CuCO3 mixed with water, and sudden...

Bless the internet, because it turns out that by entering something like "making copper carbonate" into Google, you get a bunch of hits including YouTube videos with 12-year old kids explaining how you can make  CuCO 3  at home in a few easy steps. Thus continues my ongoing investigations into colouring clay and ceramic bodies with stuff around the house. Step 1 in making Copper Carbonate involves making copper acetate (affectionately known as [Cu(OAc)2] to some, not me) because you need this stuff to make the carbonate later. It's as easy as mixing vinegar with hydrogen peroxide in a 1:1 ratio, dropping a piece of copper into it, and waiting. Within minutes, the liquid begins to turn blue, bubbles form, and hydrogen gas drifts out (you could actually see it like a smoke, although it was too faint to photograph). No smoking or lighting matches when you do this because hydrogen is flammable - I don't know how much hydrogen was produced, but I wasn't about to exp...

Another simple way of affecting the surface of a clay body is with terra sigillata (latin for "sealed earth"). It's basically a very thin liquid slip, i.e. tiny particles of clay suspended in water through the use of a deflocculant. The deflocculant is an electrolyte that ends up changing the electrical charge on some of the clay particles so that they are not attracted to each other and therefore don't gather together in clumps or "flocks", and instead they float individually in the water. What you end up with is a liquid that you can paint on your greenware and then polish to get a shiny surface on your fired piece. For a lovely example, see this shiny Greek vase: Most terra sig recipes I found called for clay powder, water and a deflocculant like sodium silicate or "old-formula Calgon" (the kind with lots of phosphates) but since I had neither, I found some heavy-duty tile cleaner at the hardware store which is trisodium phosphate, and use...

We did the inaugural firing of our garbage can kiln on Saturday, and fired some clay pieces raku-style. It all worked amazingly well.  Well, some of the clay pieces weren't hot enough to ignite the sawdust because it took too long to put each individual piece in the can, so they didn't turn all black, but as far as the kiln goes and the raising of the temperature with the weed-burner, it worked perfectly. Only one piece cracked, and sure, looking over the schedule it's clear we went way too quickly from 400 °  to 800 ° , but we kept it pretty slow and steady from start to the crucial 400 mark anyway. And besides, it's always interesting if something goes wrong - otherwise it's hard to learn what you're doing right. Start - 12:10pm 100° C - 1:20 200° C - 2:10 300° C - 2:45 400° C - 3:15 800° C - 4:15 900° C - 4:30 915° C - 5:15 I had a few pieces that I had prepared with different iron oxide formulations, and I also f...

I've been wondering how to colour the clay and ceramic pieces I have, and of course I could go to the pottery supply store and pick up some glazes, but a) it's very far away and I don't have a car, and b) it seems more interesting to do something more 'primitive'. What could I use from around my house that would make an interesting mark? A few days ago I was out on the deck and noticed some rust stains on the wood beside the legs of a metal chair we have. Rust... iron oxide... of course! The theme then became how to get iron oxide. So I put some steel wool in a can with a bit of water and let it sit for a while. I also scraped some rust flakes off the lid of a metal can that coincidentally we're going to use when we do our raku firing next week. And lastly, after doing some internet trawling, I burned some steel wool because that apparently produces iron oxide.* The whole week long I saw rust everywhere. Everytime I walked my dog was a chance to find some ...