Glazing

Warped mug (The one with the handle)
Originally uploaded by TimsPottery.

I started doing pottery at a community studio in Oak Ridge, TN when I worked at Oak Ridge National Lab. The glazes there were mixed by the instructor and some of his assistants. Firing was done in electric kilns equipped with kiln sitters. Results were mixed.

When I moved to Oregon, I bought various ^6 commercial glazes a couple didn't work to well, and a few did. A couple of years ago, I bought a Skutt kiln with a computerized controller. I also started using a variety of Laguna clays. I got to a point where I thought I had several glazes that worked pretty well.

And then I did the Christmas present mugs. For each of my siblings, their kids, and spouses I made a mug from Laguna ^5 Morrocan Sand. I attatched a variety of images cut from slabs of the same clay onto each mug. I glazed the insides by pouring and the outsides by hand application onto the applied images.

After firing, I had cracked mugs, runny glazes, and crazing. A lot of work down the drain.

That's when I decided to learn how to make glazes. I found Mastering Cone 6 Glazes by John Hesselberth and Ron Roy. I cannot recommend this book highly enough.

The first thing I did was to mix up the glazes they recommend for testing coefficients of expansion. These are used to get a handle on the coefficient of expansion for the clay you are using. This part of the process went great. I was able to get a test glaze that would not craze or shiver when doing the heat/quench test on the clays I was using.

My next step was to get a base glossy glaze. I chose their Glossy Base Glaze1 from p. 92. I kept most of it plain, but added a little cobalt to some and some rutile to some. I glazed some mugs and pots and fired them to ^6.

And got a big, rude surprise. At ^6, the Laguna Moroccan Sand clay body I liked so much warped badly (see the picture).

So then I tried firing it to ^5 with a 20 minute hold at 2185 F and a cooling rate of 150 F down to 1500 F. And the &#%* Moroccan Sand warped and slumped on several pieces. In addition, the glaze had more of a semi-matte texture.

I made a couple of attempts by adding more boron to the glaze and using Laguna Colonial white as a control. The Colonial white came out glossy, the glazes I mixed myself were still semi-matte.

By this time, I was mainly making jellyfish (see prev. posting) and was having good results with CW as a base glaze and using a couple different glazes (Laguna Regal Blue and Laguna Blackberry) as light overglazes. So I took a hiatus from making my own glazes.

Now I am preparing to make another foray. I've done quite a bit more web research and come across a couple of different things:

1) Ravenscrag slip

This stuff sounds like the best thing since sliced slab tiles. At ^10 it is a glaze by itself. For ^6, one just needs to mix it with ~20% Frit 3134. It is supposed to go on like a dream and perform well for multilayering. I've bought some and will try it.

2) Great Results from Electric Kilns

A presentation by John Hesselberth that in part discusses factors that effect glazes. Most notable for me was the section showing the effects of slow vs fast cooling.

I now have 3 possible suspects for my glossy glaze turning out semi-matte:

a) Not being fired high enough. As a result the glaze is not melting completely. This would be very bad for glazes used with food as it would lead to leaching.

b) The glaze composition is not what I think due to variations in materials. This could result in unmelted glaze.

c) Cooling too slowly. Micro crystals could be forming as the glaze cools. This would not necessarily mean a glaze that would lead to leaching, but it's still not the glossy glaze I am after.

So as I look forward to glaze development, I will be revisiting the Hesselberth and Roy Glossy 1 glaze and pay attention to the cooling rate at the same time I test glazes based on Ravenscrag Slip.

I haven't talked about glaze software, but undoubtedly will in a future post. I am using Digital Fire's Insight software on a trial basis. I'm sure that when my trial ends I will be purchasing it.

First Sale (sort of)

IMG_2715
Originally uploaded by TimsPottery.

Last fall, my neice asked me if I would donate something for her school's auction. Of course I was flattered and said I would. In January I sent her this set of 3 slab built vases (Laguna ^5 Bmix, Laguna Colonial White glaze fired to ^5). Yesterday, my sister told me that they were displayed at the auction with some silk orchids on the same same table as the Waterford Crystal (I'd like to think there's a logic beyond "just put it over there" to that placement). My sister didn't know the final selling price, but the last bid she saw on them was $100.

At least I now know I'm not the only one who thinks my pieces are worth paying for.

First Sale Display

Jellyfish for Sale
Originally uploaded by TimsPottery.

My next door neighbor, "Cedar" Caredio is a talented woodcarver as well as friendly individual. He belongs to a group called Oregon Crafted which publishes a guidebook and sponsors artitst studio tours on the first weekend of every month. Cedar was kind enough to let me display some of my jellyfish beside his carvings. So I took him up on the deal.

Am I Really a Potter?

I have been doing pottery as a hobby for eight years and have thought often when I could legitimately call myself a potter. This weekend, as I was putting prices on pottery jellyfish I made for an artists’ home gallery event, it occurred to me that if I was selling pottery I made, I was probably a potter. Now all I have to do is for someone to buy something and I will feel that I am justified in calling myself a potter.