Sunday, 28 April 2013

Kiln fillers

When we fired the Manor Stokes wood kiln in February, there were little gaps left between vases and bowls where we could have sneaked in quite a few small pots. It seemed such a waste, I vowed to make a stack of little pieces for next time, and today I set out with the intention of making a series of egg cups. I've never made an egg cup before in my life, and soon realised that I couldn't quite remember exactly how wide an egg is, and how much space I'd need to allow for clay shrinkage. So for the first hour I made shot cups instead:

Eggs for lunch and now I have a hard-boiled egg to use as a measure. My design will be nothing complicated..just a small cup with a flared rim to accommodate the egg.

I'm starting to glaze other pieces for the wood firing too. This is a carved sake cup, which I cracked deliberately by pushing out the sides. Actually the crack is rather bigger than I intended, but it could be filled half way without it leaking. And half a cup of this size is probably enough for most people!

Several pieces made of the pink grogged stoneware have been slipped and bisque fired. I test fired a small sample the other day to 1300 degrees C and it survived okay, so I'm hoping wood firing won't present any problems (namely, the dreaded bloating). These two cups will be fired with a transparent glaze which should reveal some of the darker clay beneath:

I've produced quite alot of textured pieces this week without a clear idea about how they will be fired or how they should ideally look when finished. Most likely, they will be fired unglazed..I think adding large amounts of ash or glaze is likely to obscure the texture..but on it's own, it may come out a little dull. Actually, making the surface itself look interesting before firing is the most difficult part..

Back to the egg cups. It's hard to resist making the top section into a rounded form, partly to allow for different sized eggs ..the ones I threw today ended up looking a bit like chess pieces:

I made six and I'll measure one of them to see how much the diameter shrinks after firing. Making alot of small pieces is quite's rewarding to be able to see a finished piece on the wheel in a few minutes, and you get into a nice rhythm of throwing.

Friday, 26 April 2013

New texture and a new saggar

Yesterday I bought four kiln shelves, some shelf supports, a saggar and some shelf off-cuts to act act as fire-grate bars in my mini wood kiln. Everything apart from the saggar was second-hand, and I had the kiln shelves cut to shape so that three of them can become the roof of the kiln and the firebox. Remains to be seen whether they crack..they're not really designed to be used in that way.

Here's the new saggar, it's just deep enough to contain three to four cups, but hopefully it will last for many firings. The top should be perfectly even so, provided the shelf is flat, it should make an air-tight seal, although it doesn't matter if a bit of oxygen gets in:

In the old days in Stoke-on-Trent, every bottle kiln used saggars to protect the ware from smoke and debris, and they were two a penny, practically disposable. Now the ceramics industry has declined and technology has moved on, they are as rare as hen's teeth..and as far as I know, no company makes them in the UK any more.

Playing around with rough textures again too..this is the latest concoction:

The clay is only half-dried in this photo. Not sure how it will fire (that is to say, whether bits will erupt and fall off!), but at the moment it makes me think of toad skin.

And finally, I took a picture of these pots mainly so I can remember which glaze I put on them. This is a matt ash glaze with an addition of rutile:

I can't wait to see what colours these will fire to, in oxidation and reduction. One of them will be fired in the smokeless wood kiln in Sheffield next week and the other two in the electric kiln.

Monday, 22 April 2013

Anyone for sake?

Really, I should be spending more time making cups for coffee rather than cups sell much more easily here in the UK. But I can't resist making them, I enjoy the process so much..and very often, when throwing off the hump, I end up with a ball of clay which is just the right size for a little cup, rather than a big mug!

Sunday, 21 April 2013

Hurray, warmer weather at last!

It's been lovely and warm the last few days..still a bit chilly first thing in the morning but I can't complain. Don't you find a good dose of sunshine really increases one's creativity and energy no end? I had a sudden creative spurt this week and I put it down to the sun causing endorphins to swirl around in my brain. Well, that's my theory, anyway.

A few of the things I'm working on at the moment: 
Large tea bowl in pink stoneware.

A bit of fun: "tortoise" coffee bowl

Texture experiment on two inch tall vase

Texture experiment on 4 inch vase
Yunomi 4.5 inches tall


Sunday, 14 April 2013

Massive carbon trapping?

This sake cup has been fired twice in a sealed container to cone 10.. both times it was fired on shells, the second time with charcoal and dried banana skins. Unusually, this saggar seems to let barely any air in..only a small amount of combustible is needed to achieve complete reduction. The evidence being that much of the charcoal remains unburned after the firing.

The glaze is raw wood ash over shino..there seems to have been a huge amount of carbon trapping which has produced an almost pure black in the shinier parts. There are some nice dark purples going on in there too. What do you think of the colours? I'm tempted to re-fire this piece in oxidation which will remove much of the carbon again..that might produce some interesting effects.

Update: did a low bisque firing to 800 degrees C, so popped it back in the kiln, but in a sealed saggar with charcoal as I didn't want to lose the dark colours completely. Here's the final result..maybe not easy to see on these photos, but the reddish purple hues have come out a little more, especially on the inside:

I don't usually go for very dark colours in a big way, but I'm very happy with this piece now..and having expended so much time and effort on the making, I've grown quite attached to it.

Saturday, 13 April 2013

Orange and black

sake cup, 3 ins tall

sake cup, 2.5 ins tall

Fired to cone 10, 1300 degrees centigrade.

Thursday, 11 April 2013

Ash glaze test results

Opened the electric kiln this morning and was pleasantly surprised by the "Ki-Seto" glaze tests I did. They all came out quite dark and not terribly yellow, but I can see potential in all of them. First up is the fake ash glaze plus yellow iron oxide on the left:

I expected this would be runny, so it was placed on a broken bit of kiln shelf..and run it did! Less iron oxide next time may reduce the fluidity of the glaze a little. The Leach Old Seto Yellow (on the right above) came out very nicely, if a little thin in places. The glaze ran but stayed on the edge of the foot, luckily. Here is the test piece with Old Seto but only half the amount of ash: 

Still fairly runny, this glaze produces some yellowish hues where well as patches of translucent, amber-coloured glaze.

Finally the Nami-Jiro glaze with additions of yellow iron oxide: 

I like the rich, matte yellow hues produced on these pieces where the glaze is thicker, but overall, the brown tones are not very exciting. The problem with many of these heavily ashed glazes is making the slop thick enough, and then preventing the glaze from deflocculating. (Update: having read a piece about Hamada's glazing technique, I've realised that for this type of ash glaze, I need to bisque much lower, perhaps only 800 - 900 degrees C. That should allow the clay to take a thicker coating of glaze, but of course one then needs to consider how to deal with bigger potential glaze runs..)

This last piece was coated with a matte ochre-ash glaze I've used many times. It also produces lovely yellow tones where thicker, but this glaze slop was made with mainly pine wood ash, so it turns a kind of blue-green  when applied very thick. The shiny patches are splashes of Oribe, turned amber by the iron in the ochre ash glaze: 

Torn vase, approx. 5 inches tall

Sunday, 7 April 2013

New clay, slips and glazes

I'm going through another experimental phase, trying out some new things and refinements of old things. First is a new clay from Potclays (new to me that is) called pink, grogged stoneware. I'm hoping this high-iron clay will be able to withstand wood firing and give interesting results under a white slip, and possibly under shinos. This tea bowl was been made with it, and I also tried out a different way of carving the footring, using a loop tool:

In my continuing search for the perfect black slip, I've also prepared a Gosu slip, based on one of the recipes in John Britt's "Complete Guide to High Fire Glazes". It's made with manganese dioxide, red iron oxide and cobalt oxide plus a little red clay. In John's book it says that the Japanese often mix their Gosu slip with a little green tea to aid application, so in the absence of green tea I tried it first with stewed, British tea. And I must say, brushwork with this mixture is a doddle due to the fine particle smooth it's wonderful, with nice sharp, dense lines. This slip is designed to produce a greyish colour (hence "gosu", meaning mouse in Japanese) under a thin layer of shino, and is most likely unsuitable for use under a transparent glaze with such high oxide content.

Another current area of interest is Japanese, Ki-Seto glaze, a kind of satin-matte, yellow glaze containing wood ash and iron oxide (this page from e-Yakimono provides a summary of Ki-Seto terms) . So far, I've been unable to find a definitive Japanese recipe for this glaze, or establish whether one exists..many of the Ki-Seto pieces I've looked at online seem to vary alot in terms of the yellow colour, and the texture and transparency of the glaze. There is this well-known recipe called Old Seto Yellow (from Bernard Leach, I believe) which may be an approximation of the traditional Ki-Seto:

cone 8-10 /Leach:

Feldspar 25
Medium ash 50
Ochre 25

I will try the above recipe, although I suspect the material I have here is a pure yellow iron oxide, much stronger than yellow ochre which is normally an earth pigment with a high clay content. In fact I just read another blog where a potter said they tested the Leach glaze and it came out matte purple, which I think  may have been caused by an excess of yellow iron oxide. 

My version will probably look something like this: 

Potash feldspar 25
Oak wood ash 50  (I will also do a test with 25 of wood ash for comparison)
Kaolin 25
Yellow iron oxide 5

I'm modifying a Nami-jiro recipe and a fake ash glaze as well, to see if I can create an acceptable, similar version rather than an exact copy of Ki-Seto. But if anyone happens to know exactly how Japanese potters prepare it, and you'd like to share your knowledge, I'd love to hear from you!

Glaze test pieces

Above photo:  left is fake ash glaze with y.i.o., middle two are Nami-jiro with y.i.o., right is Leach Old Seto, altered as above. These will be fired to cone 10 in oxidation.