I thought I'd have a first go at filming myself throwing today. Must say, I did feel quite conscious of the camera, and it was more difficult to concentrate and lose myself in the process. I chose the first clip as I had a couple of problems with an air bubble in the clay and the bottom starting to sag, which maybe makes it a little more interesting to watch. Apologies for the noisy wheel (bearings are going) and my noisy stool..it's one of of those weeble-wobble Ikea stools with a base wider than the seat. I'm always tripping over the thing!
Sunday, 11 March 2012
Saturday, 10 March 2012
Making lidded jars
Last week I made several of these lidded jars or urns. I was inspired by images of ancient megaliths and I wanted to create some vessels which communicate a similar kind of heft and gravitas. I don't know how far I've succeeded..it's difficult to achieve that with small pieces, so at some point, I'd like to make these on a much larger scale. Making the lids is challenging to say the least, and I'm still trying to work out the best way of doing that from a closed form.
At the moment, I'm adding the inner lid flange by hand, as a coil, then pinching it out, letting it dry a little, and then trimming and scraping it down to fit. It's quite a fiddly and time-consuming process.
I'm already thinking about how I should glaze these jars..I will probably fire them with the lids in place, so I need to use a glaze which definitely won't run. Traditional shino is one possiblility or perhaps some black slip decoration covered with the matt ochre-ash, which I might try pouring over one or two of them. The two pieces below have this matt ochre-ash glaze:
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| Lidded jars drying, approx. 6 inches tall. |
At the moment, I'm adding the inner lid flange by hand, as a coil, then pinching it out, letting it dry a little, and then trimming and scraping it down to fit. It's quite a fiddly and time-consuming process.
I'm already thinking about how I should glaze these jars..I will probably fire them with the lids in place, so I need to use a glaze which definitely won't run. Traditional shino is one possiblility or perhaps some black slip decoration covered with the matt ochre-ash, which I might try pouring over one or two of them. The two pieces below have this matt ochre-ash glaze:
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| Beer cup, six inches tall |
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| Bowl, approx 3.5 inches tall |
Tuesday, 6 March 2012
Feels like spring at last!
Today feels like the first proper day of spring. Started off quite misty this morning but this afternoon the sun was really bright and warm, and I even put some pieces outside to dry. Daffodils are blooming and trees are starting to bud, including my Japanese larch bonsai, which has pine cones on it for the fist time in sixteen years.
And then I just took this shot for the colours:
Now I really must get back to throwing those pots I was supposed to make this morning!
And then I just took this shot for the colours:
Now I really must get back to throwing those pots I was supposed to make this morning!
Friday, 2 March 2012
Pots can definitely grow on you
I made this little pot some time ago now, and I've glaze-fired it three times..once in reduction and twice in oxidation. Each time I wasn't really satisfied with the finish and brushed on another layer of glaze, and even when I took it out of the kiln last time, it didn't strike me as being particularly attractive. It's been knocking around in my workshop for several months, and I kept picking it up, turning it round, putting it down, wondering whether I should bother to put it in for a fourth firing.
Then the other day I took it outside and looked at it more closely. In the bright daylight I could better appreciate the subtle sheen of the ochre-ash glaze which contrasts with the harsher mottled areas of burned-out iron. I began to like the way this glaze shows every detail of the clay surface, every single mark left in the making process, and the way it pools in the crevices into darker shades of grey-green.
Pots can slowly grow on you...or maybe as with people, it becomes easier to accept their imperfections once we have lived with them for a while..
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| Carved pot with ochre-ash glaze, 3.5 inches tall |
Then the other day I took it outside and looked at it more closely. In the bright daylight I could better appreciate the subtle sheen of the ochre-ash glaze which contrasts with the harsher mottled areas of burned-out iron. I began to like the way this glaze shows every detail of the clay surface, every single mark left in the making process, and the way it pools in the crevices into darker shades of grey-green.
Pots can slowly grow on you...or maybe as with people, it becomes easier to accept their imperfections once we have lived with them for a while..
Tuesday, 21 February 2012
Blistering black slip problem..a possibe solution!
I've just found a very interesting article by Vince Pitelka at the Appalachian Center for Craft, Tennessee Technological University, which goes some way to explaining why my black slip is bloating and blistering at cone 8 and above:
http://iweb.tntech.edu/wpitelka/syllabi-handouts/handouts/decorating%20slip.htm
This is what he says about slips (or engobes) which contain 10% iron oxide:
"There is a fundamental problem with any all-purpose base slip recipe, arising whenever making black and brown slips, which might contain 10% iron oxide. Red iron oxide is refractory (melt-resistant), but any reduction firing and all high firing will convert it to black iron oxide, a very powerful flux. A slip base formulated from a standard porcelain body might contain 25% potash feldspar, and the addition of 10% iron oxide will produce a serious flux overload, often resulting in boiling, blistering, and crawling at high temperatures. To address this problem, we use two versions of the base slip recipe. One contains 20% potash feldspar, and is intended for all colors except black and brown. The second version, intended for black and brown slips, contains 12% potash feldspar in order to compensate for the addition of the iron oxide."
So, as well as decomposing above 1232 degrees C and letting go of oxygen molecules, red iron oxide also converts to black iron oxide, which has ten times the fluxing power of r.i.o.!
I haven't used porcelain slips (or engobes) but I was using a red clay as the base for my slip, which may contain around 5% or more r.i.o. and then adding an extra 4% r.i.o., so the slip may have become overloaded with it. Both manganese and cobalt also act as fluxes, thereby adding to the problems. As a next step I plan to make a dark slip (probably more dark brown than black) using a stoneware clay plus 6% black iron oxide, 4% manganese dioxide and 2% cobalt oxide. I'm hoping that the use of black iron oxide (FeO) will avoid the release of oxygen under the glaze, and the lower concentration of iron will reduce the likelihood of the slip layer blistering.
The other interesting point made is that thin applications of slip can be made opaque by adding zircon, something I'd only used previously to make pure white glazes.
Here's one of my bottle vases from the last firing, with poured black-slip decoration..this one came out with no faults:
http://iweb.tntech.edu/wpitelka/syllabi-handouts/handouts/decorating%20slip.htm
This is what he says about slips (or engobes) which contain 10% iron oxide:
"There is a fundamental problem with any all-purpose base slip recipe, arising whenever making black and brown slips, which might contain 10% iron oxide. Red iron oxide is refractory (melt-resistant), but any reduction firing and all high firing will convert it to black iron oxide, a very powerful flux. A slip base formulated from a standard porcelain body might contain 25% potash feldspar, and the addition of 10% iron oxide will produce a serious flux overload, often resulting in boiling, blistering, and crawling at high temperatures. To address this problem, we use two versions of the base slip recipe. One contains 20% potash feldspar, and is intended for all colors except black and brown. The second version, intended for black and brown slips, contains 12% potash feldspar in order to compensate for the addition of the iron oxide."
So, as well as decomposing above 1232 degrees C and letting go of oxygen molecules, red iron oxide also converts to black iron oxide, which has ten times the fluxing power of r.i.o.!
I haven't used porcelain slips (or engobes) but I was using a red clay as the base for my slip, which may contain around 5% or more r.i.o. and then adding an extra 4% r.i.o., so the slip may have become overloaded with it. Both manganese and cobalt also act as fluxes, thereby adding to the problems. As a next step I plan to make a dark slip (probably more dark brown than black) using a stoneware clay plus 6% black iron oxide, 4% manganese dioxide and 2% cobalt oxide. I'm hoping that the use of black iron oxide (FeO) will avoid the release of oxygen under the glaze, and the lower concentration of iron will reduce the likelihood of the slip layer blistering.
The other interesting point made is that thin applications of slip can be made opaque by adding zircon, something I'd only used previously to make pure white glazes.
Here's one of my bottle vases from the last firing, with poured black-slip decoration..this one came out with no faults:
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| Bottle vase, approx. 3.5 inches tall. Oxidation firing, cone 9. |
Friday, 10 February 2012
Tetsuya Kowari, Ceramic Artist
I recently acquired this oribe bowl by Japanese potter, Tetsuya Kowari. Isn't it wonderful? The glaze combines so beautifully with the rough texture of the clay, and inside the dark glaze has pooled, creating these amazing crystals and rainbow-like colour effects. I had no idea that crystals could form like this in a copper glaze. I'm guessing it requires very slow cooling to create them.
Kowari-san also produces fabulous anagama-fired, ash-glazed pieces. More of his work can be seen here at the Naganawa Gallery: http://shop.yumetenpo.jp/goods/goodsList.jsp?st=naganawa.jp&category=11:5&action=category
Kowari-san also produces fabulous anagama-fired, ash-glazed pieces. More of his work can be seen here at the Naganawa Gallery: http://shop.yumetenpo.jp/goods/goodsList.jsp?st=naganawa.jp&category=11:5&action=category
Experiments with shino, oribe and under-glaze slips
Well, I just about managed to get a firing ready last weekend, despite the sub-zero temperatures. I tried out several new approaches to decorating and glazing, some of which worked really well, others much less so. For the shino-glazed pots I was using a new saggar, the rim of which turned out to be slightly uneven. Some air must have leaked in between the rim and the kiln shelf (which I use as a lid), making a few of the pots oxidise and the glazes bubble and blister very badly. I'll have to go back to sealing the gap with kiln fibre.
The two pots below have crawled quite alot, but I still like them:
Another experiment was to apply oribe glaze over an iron oxide slip. I wanted to leave some areas of the clay body exposed, so on this small jug I brushed the glaze on:
I'm very pleased with the outcome and will use the technique again. I think maybe the glaze needs some extra copper oxide to make the green darker, and so it will flux and run a bit more..just need to be careful it doesn't end up all over the kiln shelf! With the sake cup below, I masked sections with a polyurethane varnish (instead of using wax), then dipped the pot in the glaze as normal. This worked very well, except when the pot was fired, the varnish burned, peeled off and took some of the (unfired) iron oxide slip with it. Note to self: always apply the iron oxide before the bisque firing.
Finally, I made a few vases and coated them with black and then white slip while at the leatherhard stage. After bisque firing, a transparent ash glaze was applied. These pieces really have me puzzled since one came out perfect..
..while two other pieces were covered in tiny blisters under the white slip, like the bloating one would get in over-fired earthenware. I figure that the bubbles were caused by gases being expelled from the black slip layer, and the white slip and viscous glaze have formed an impermeable barrier. Hmmm, that's my theory anyway..and I'm not sure how to solve the problem, except by experimenting with different formulations of black slip.
I was wondering if using black iron oxide (Fe0) would help as it won't decompose, releasing oxygen as red iron oxide does. If anyone has any advice or thoughts on this one, I'd be really interested to hear them.
The two pots below have crawled quite alot, but I still like them:
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| Sake cup, approx. 2.5 inches tall |
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| Chawan, approx 4 inches wide |
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| Chawan with clam shell marks |
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| Jug, oxidation firing, cone 9 |
I'm very pleased with the outcome and will use the technique again. I think maybe the glaze needs some extra copper oxide to make the green darker, and so it will flux and run a bit more..just need to be careful it doesn't end up all over the kiln shelf! With the sake cup below, I masked sections with a polyurethane varnish (instead of using wax), then dipped the pot in the glaze as normal. This worked very well, except when the pot was fired, the varnish burned, peeled off and took some of the (unfired) iron oxide slip with it. Note to self: always apply the iron oxide before the bisque firing.
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| Sake cup, oxidation firing to cone 9 |
Finally, I made a few vases and coated them with black and then white slip while at the leatherhard stage. After bisque firing, a transparent ash glaze was applied. These pieces really have me puzzled since one came out perfect..
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| Bud vase, approx. 4 inches tall Oxidation firing to cone 9 |
..while two other pieces were covered in tiny blisters under the white slip, like the bloating one would get in over-fired earthenware. I figure that the bubbles were caused by gases being expelled from the black slip layer, and the white slip and viscous glaze have formed an impermeable barrier. Hmmm, that's my theory anyway..and I'm not sure how to solve the problem, except by experimenting with different formulations of black slip.
I was wondering if using black iron oxide (Fe0) would help as it won't decompose, releasing oxygen as red iron oxide does. If anyone has any advice or thoughts on this one, I'd be really interested to hear them.
Never give up..the best is yet to come!
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