In my first soda firing, I learnt a lot about the kaolins and other clays in the magic cave of materials at USU. On the basis of my test tiles, which you an see in my last blog post, I was able to make some educated guesses about which materials I wanted to include in test clay bodies.

I set about making 50lb batches of 8 white (or at least pale) stoneware blends, and 10lb batches of 11 different porcelain blends. Making the stoneware bodies was easy in the little bluebird mixer at USU; I was able to make all 8 of the stoneware clays in an afternoon and bag them up to sit a week or so before I threw them.

The porcelains were mixed dry in separate 5 gallon buckets. I added water and let them sit to absorb without mixing overnight. I added water until they were the consistency of thick cream, throughly blunged them and set them out to dry in plaster beds lined with clean sheets. They took maybe 3/4 days to dry to the point that I could take them out and make them into coils to finish drying up. This process was fairly time-consuming and I had to be really on top of how the porcelains were drying. Keeping track of which blend was which was also a challenge. I marked the plaster beds and sheets but there was some head scratching nonetheless.

Next I decided to make several yunomi (cups) with each clay and a couple of wide open bowls too. The idea was to make forms with trimmed feet in order to give me more information about how the clays operated and looked. I also decided to set the bowls on their sides in the kiln to encourage interesting soda flashing, and more importantly, to see if the clays would warp. Again, keeping track of the 19 different clays as I was making was a challenge; I had a very technical system of torn slips of paper reading “14” or “3” that sat on my ware boards next to the thrown forms.

The system worked, but was not foolproof. Unfortunately, I am a fool. Once or twice, the little slip of paper got shisked off my board of pots by a gust of wind or a stray corner of a sheet of plastic. At these moments, I had to use my limited powers of logic to figure out what the clays were and re-label them. Shockingly I managed to get all the pots trimmed and labelled without major confusion or tears.

I had more of each of the stoneware clays so threw some extra pots with these, and experimented with a few slips on them too. This helped fill the kiln. I packed the kiln looser this time, trying to put larger pots in the center of shelves with smaller pots towards the edges.

From my first firing, I did not know how much of an impact the reduction cooling had, so this time I aimed at an oxidised firing. I wanted to see if my slips/new clays would be totally bland without any reduction. It felt kind of wrong to be firing in this way, just ignoring body and glaze reduction, and cooling the kiln naturally in oxidation. But it was an experiment.

Alright, here’s the results… (I will discuss the results below the pictures).

RESULTS

First thing of note was that the pots were not oxidised. This is what I had been aiming at, so it was a little confounding at first. In retrospect I didn’t pay enough attention to the level of gas entering the kiln. I kind of thought that if I did not intentionally reduce the atmosphere then it would be oxidised or neutral. This was clearly not true. I think to truly oxidise the kiln I would have to fire over a longer period with less gas and more air throughout.
However… the results were pretty nice, even though it did not go as planned. What did I learn? It is way easier to reduce pots in this kiln than expected. I think body reduction is unecessary, but will further investigate this to make sure.
In general the colors were brighter than in my first test firing but there was less drama on the surface of the pots. There were less deep red tones, but also perhaps less distinct flashing lines. Somewhat softer flashing and softer surfaces in general.
I used 15lbs of soda. The first 5 went in as spray, but I got fed up with how long it was taking and my nozzle was acting up (I partially melted it haha), so decided to make some burritos and shove them in. I mixed damp soda, baking soda and rice hulls and wrapped them in newspaper to introduce them.
The soda went in over 3/4 hours this time instead of 6 hours in the first firing. Not a much different sodarisation level on the pots… I think because the gas and air pressure was pretty high and I didn’t crank the damper in as much. Also less carbon trapping. And less blue glassy drips off the shelves onto pots. Had a lot of that in my first firing. Could have been partly due to the shelves not having been cleaned as thoroughly before I fired that first time.
The clay tests proved very interesting. There were significant differences in how they flashed, how glassy and vitrified they were, how much they shrank. Some excellent information. Some of the test bodies clearly were not going to work; a couple of them warped really badly or cracked.
It was clear from having at least a cup and bowl of each clay that the placement in the kiln was crucial to the resulting surface of the pot. This leads me to realise I need to put these same test bodies in several more firings to see how that affects the results.

Below are a few examples of a few of my clay body tests. The first had some strange cracking on the bottom. I think it was from not having wedged the clay thoroughly enough. You can kind of see it on the base here. I was perhaps a little fast and loose when prepping and making this particular bowl.