Friday, 17 August 2012

Testing, testing.

Just a quick post to show some of what came out of yesterday's firing. I fired a few test pieces with the fen slip as a glaze and took them to cone nine. The result was a rather horrible dull, blacky brown, but in oxidation I wasn't really expecting much from it. More exciting was this white ash glaze I mixed up last week..I placed this over a normal off-white stoneware (left) and over a 50/50 mix of the fen clay and raku.

Sample on left has black and iron underglaze decoration

Above sample on right, close up

The glaze on the right has turned a kind of granite-like pink-grey and the black underglaze a dark bluey green..quite remarkable! There are also yellow-brown spots coming through from the clay body...I like this finish very much.

Here are a few of the pots:

Carved sake cup with ash glaze

Carved sake cup (no glaze but soaked in soda ash solution) with fen slip inside

Sake cup (no glaze) with fen slip inside

Sake cup detail

Sake cup. Ash glaze over iron decoration

Oribe cup, or yunomi
Oribe cup, or yunomi

I was getting tired of finding the odd burst bubble in the oribe glaze, so I added a tablespoon of frit to the mix, hoping to make it less viscous. It does seem to have helped with bubble and crater formation, but perhaps it also made this last yunomi's glaze crawl. It was on the top shelf whereas the non-crawled glaze was on the bottom where it may well be cooler. Also the carving pattern on the crawled pot is less vertical, so the glaze may have pooled more. (Actually, I think it's crawled in a way which adds interest, rather than making it really ugly as crawling sometimes does) So I'm not sure whether adding frit was a great idea or not..I think I need to find a new oribe glaze.

Thursday, 16 August 2012

Throwing jars, lidded and unlidded

I joined facebook recently, and it's proving to be a wonderful place to find and view ceramics from all over the world. I'm currently throwing some small and medium sized jars which have been inspired by pottery from countries such as Japan, China, Taiwan, South Korea. Here is an example of a small jar I threw the other day, which has been bisqued:

There is something about this form which really appeals to me..sturdy and vaguely anthropomorphic, it has what you might call "presence". I was already making bottle-vases with this kind of shape, but taller and narrower..this form is more relaxing to make..easier to get fingers inside to refine the outline. I'm thinking that some of these will make very nice tea caddies, perhaps with wooden lids. The larger ones will have ceramic lids, rather like Chinese and Japanese ginger jars.

Tuesday, 14 August 2012

Mini wood-fired kilns..a possibility?

Two questions I'm seeking answers to at the moment:

- is it feasible to build a mini wood-fired kiln?
- if so, what is the highest temperature it could be fired to?

I'm exploring the possibility of designing a very small kiln for use in a suburban environment, so ideally it has to produce no more smoke than a household barbecue. Last week I created a simple up-draft prototype using normal house bricks to build a firebox and a kiln chamber and chimney made from cylinders of kiln fibre. The chamber was large enough for around nine small-to-medium pots placed on two layers of shelving.

The kiln was stoked with charcoal and wood for around five and a half hours (that is to say, until I ran out of fuel!) and temperatures in the firebox were high enough to make the metal grill slump. The 5-inch high ember pile turned pale yellow and the flames a beautiful lavender-blue.

I was hoping to get to high earthenware temperature in the chamber, but we didn't get there...even cone 05 didn't go down, but the temperature was high enough to sinter the fen slip I'd applied as a glaze to the inside of a few of the pieces. By the end, the kiln fibre was glowing a bright orange and you could watch waves of flames surging up the walls of the was worth five hours' hard labour just to see that.

One thing I was pleased about was the low level of smoke produced..generally, the fuel burned very efficiently and smoke only became evident when a damper was placed over the top of the chimney. Once things got toasty in the chamber, seven inch flames would shoot from the chimney as wood was piled on..pretty impressive for a kiln less than five feet tall!

This design was just cobbled together using stuff I had lying time I plan to build one using H.T.I. bricks and a second layer of one-inch kiln fibre. I will also reduce the height of the kiln chamber and make the chimney taller...hopefully that will make much higher temperatures achievable.

I've yet to find much on the web about mini wood-fired kilns. If anyone has any ideas or links, I'd be glad to hear about them. I do remember a chap demonstrating a tiny, portable kiln at a ceramics fair back in 2007. It was fired with charcoal, and he reckoned it could reach stoneware temperature. The chamber was miniscule though, as were the pots he put in there.