Tuesday, July 30, 2013

Material World

This month I have mainly been testing glaze materials and porcelain clay bodies:

Every colourant, opacifier, some fritts, ashes, salts, ochers,engobes and some unknown glazes from my lab. This is what they look like before they've been fired

The shelf on the right contains materials collected from potters past, some I won't bother testing because there's not enough to be worthwhile, but I do like the eclectic collection of glass jars and materials.

Some of the materials from the shelf that I will be testing including a bag of 'Sunset Orange'. Looks like something from the 1950's.  The large bag of Smith & Smith glaze turned out to be a nice old school oatmeal glaze.

Side-handled teapot, teabowl and small breakfast bowl, along with some porcelain beakers from a recent firing. Glazed in celadon.

Cutting some shelves to size for the small kiln from old broken shelves discarded from an old pottery studio

All that remains of one of the bags of materials, I could just make out things like 'nepheline syenite' and 'kentucky ball clay'

Shrinkage and warpage bars after firing 1300 degrees C. The shrinkage bars were all under 15% shrinkage, made from throwing-consistency clay. The warpage bars all warped except the pipe clay. It was surprising that the commercial stoneware clays warped about the same amount as my own homemade stoneware and porcelain clay bodies.

These are some recently acquired materials that had been left in unlabelled bags. To get a better idea of what they all were, I had to fire a small amount of each one to see how each one reacted at 1300 degrees C. They all looked like white/grey powder but fell into four main categories: Nepheline Syenite, Silica, Kaolin and Ball Clay.

The main materials for clay bodies and glazes eg: silica, clays, fluxes, calcium carbonates, feldpars, fritts, etc.

These are the main colourants after firing to 1300 degrees. I added a strip of clear glaze down the left side of each example. Some of the colours burnt out at this high temperature but others didn't look too bad.

Unnamed materials test results. 1. is unknown pink stuff from Glenfalloch Pottery,  fired to an opaque white glaze, most closely resembling the Zircon Fritt, which you can see in the picture below. The Zircon Fritt was resourced from a retired potter. I haven't had any experience with these materials, as this is the first time they've been tested. 2 looks like Nepheline Syenite and 3 Silica.  7 is Kaolin.

Zircon Fritt is top left, pink stuff second from bottom right

Homemade porcelain clay. Throws well, vitrified with a good glaze fit. Glazed in my own clear glaze with no crazing. Not bad for a first attempt at porcelain, very simple, compared to the literature I've read that made it sound so complicated, ie, porcelain being not very plastic for throwing, prone to warping, 'glaze shivering' etc. etc. etc....

Kitten in a terracotta pot:  'My Cat Likes to Hide in Potses'

Thursday, July 4, 2013

Shades of Clay

Recently I was lucky to get my hands on some very old clay and pottery materials, but unfortunately nobody remembers exactly what they are.  They were stored for thirty years underneath a pottery which is now closed. Rumour has it that they originally came from the clay factory at Benhar, and could be materials such as kaolin, ball clay, and feldspar...and then there is some mysterious pink stuff.  This could be a fritt, a glaze...or even a fertilizer, who knows! To anyone who doesn't know it just looks like dirt. Excavating them was a mission, as a few bags had split open over the years spreading clay dust everywhere, and I had to cart them along a muddy goat track above a steep drop to a creek. Some of those bags weren't exactly light either.

Various shades of clay ranging from yellow-white, white, grey-white, to grey. Some could be feldspar, silica or kaolin clay?

To test my clays, I'll add a little bit of water to see how it reacts. If it's a clay, it'll be sticky, plastic, buttery, waxy - and feel like clay - but if it's a feldspar or a silica it'll pack down hard like a rock in the bottom of a test container. Preliminary tests have shown that some of these materials could also be a glaze. And then there's still the mysterious pink stuff...

Some fire bricks intertwined with roots of the 'paper tree' (fuschia?) Reminiscent of a scene from Tomb Raider.

Breaking up bags of rock-hard pipe clay (?) under flourescent light, at night. This clay has a beautiful waxy feel - it could even be a fire clay. To test this, I'll fire it in a kiln to 1300 degrees Celsius to see if it vitrifies. If not, I might add some feldspar and try to construct a workable clay body.

Midwinter is a good time to clean up the tools that I've made and collected over the years. Seems like a lot but I only ever use half a dozen at a time.

Buckets of pipe clay (originally intended to make sewage pipes?) and our new kitten. I found him in the middle of the road a couple of months ago on the way out of the local 'Refuse Recycling Centre' and took him home. He's quite a character and full of curiosity, he's always on the go.

Making my own porcelain clay body - and I'll do these tests with the other clays as well. They are a warpage bar, a shrinkage bar, a small thrown beaker and a test tile to test glaze fit and vitrification. From this I should be able to formulate a throwable clay body, in porcelain and South Stone (stoneware).

I am also planning on testing everything in my glaze lab so I have something to compare these results to. A couple of years ago I got some glaze materials that also need tested so I might as well do that while I'm at it. But that will have to wait for the next blog post.