Sunday, 28 July 2013

Experimental gas kiln project

Recently I've become very interested in black glazes and the Japanese technique of Hikidashi, where pots are pulled straight from the kiln at top temperature and allowed to cool extremely rapidly in the air, or immersed in water. I wanted to find a way to fire tea bowls quickly outside, with a view to designing a small kiln with a removabe roof or wall .. I could then use (very long!) tongs to grab the bowl at over 1200 degrees C and place it in water or a reduction chamber, as is done with raku pots.

As I've not fired with gas before, I set up a little test kiln yesterday. The kiln has a very small chamber with only enough room for three small pots or maybe one large tea bowl. I was over-optimistically hoping I could fire it to cone 10 in less than 2 hours, in the event it took 4 hours but still pretty quick compared to a large gas kiln.

I was really happy to get cone 10 to bend (1285 degrees C on the pyrometer) since the kiln design was rather ad hoc, rule-of-thumb, and quickly assembled. Surprisingly, the results were very pleasing .. I would have liked a little more reduction but I need more practice and knowledge of how to create heavy reduction in a gas kiln.

Here are some photos of the firing and two of the pots:


Thanks for reading.

Saturday, 27 July 2013

First Nuka glaze is a big surprise!

I fired the electric kiln to cone 10 on Friday and tried out a few more new glazes on trial pieces. The biggest surprise was the Nuka glaze recipe which I put over a dark iron glaze, made with the earthenware clay from the Cambridgeshire fens (huge thanks to fellow potter and friend, Dameon Lynn for supplying me with some of his locally dug fen clay).  I wasn't expecting alot as Nuka is a very high silica glaze, difficult to melt even at 1300 degrees C. But this was the result:

Not only has it melted fully, it's even started to run down the pot! The blues in the glaze were also completely unexpected, as there is no material in the glaze to produce this. I think the Nuka glaze must have picked up iron oxide from the dark fen glaze and it's become reduced under the sealed surface. The iron will also have acted as a flux, helping the glaze to melt fully. Amazing! By the way, the white specs are unmelted chunks of flint (the source of silica in this recipe) .. I didn't realise how coarse this material is, so ideally the glaze needs to go through an 80s mesh sieve.

Another test was this little container:

This glaze is a mixture of a matte ash glaze containing rutile and an orange slip made with a commercial glaze stain, ball clay and china clay plus a little red iron oxide. The high clay content has produced a very matte surface but one which is very smooth to touch, almost like egg shell. The rutile and iron oxide have created subtle variations in colour .. I have a feeling this will be very good under reduction.

A few more pots from this firing .. the pieces below have the Leach, Old Seto Yellow glaze with around 35% raw wood ash:

Medium jar/vase approx 6 inches tall

Bud vase, 3 ins tall

Sake cup, approx. 3 ins tall
The Old Seto glaze works very differently on the smoother clay in the last photo. The finish is shinier, and the glaze hasn't run as it has on the coarser clay body. The glaze was applied very soon after mixing, and although I like these results, I think this recipe may work better once it has deflocculated a little. A thinner coating may produce more dark tones and greater variation in texture.

Thanks for reading!

Tuesday, 16 July 2013

Too hot to pot?

It feels that way at the moment! We're well into our second week of very hot and sticky (by our standards anyway) weather, and we're just not used to continuous sunshine without regular downpours of rain. Certainly not complaining though, this is the first dry and sunny July we've had in many years.

The heat is making me rather sluggish, but I am potting on, and I even did a bisc firing yesterday. This little pot was re-fired in the bisc to 950 C .. it's the one I already fired to stoneware in the saggar, when it came out a rather insipid beige colour. Usually when I re-bisc a saggar-fired piece it goes from dark to light, but this time the opposite happened:

The differently coloured patch underneath is still there, and has turned a very strong reddish brown, still with a metallic sheen to it. I think I'll call this the Meteorite pot.

Also from the bisc, a pot with experimental cracked texture:

The effect is interesting, but the technique involves applying texture and then throwing the pot from the inside only (i.e. pushing the clay outwards), which rather limits the forms you can make with this method.

I've also been throwing some taller, slimmer pieces like this simple Iga-style vase:

(Photo taken with Retro Camera)
And a form made in two parts and joined together:

Quite a tricky process joining the two sections when you can't get your hand inside the pot. Next time I may throw the base section with no floor and add it after joining. That would also allow me to create more of an oval form.

Time for a cold beer I think. Thanks for reading.

Wednesday, 10 July 2013

Throwing larger pieces

I'm making a conscious effort to throw larger pots at the moment, and doing it with much softer, wetter clay than normal. It's been alot easier than I expected, but I think the intense heat we've been experiencing really helps in keeping the clay upright. It could be a very different story on a damp, cold autumn day!

The height of this jar is only 8.5 inches, but to me it looks alot taller:

A fairly large tea bowl, about 6 inches wide:

And a rather "wabi sabi" chawan:

I'm fairly pleased with the form of this bowl but not entirely sure I like the curves of the rim. The footring or "koudai" (as it's called in Japan) was hand carved.