Darkoshi

The last two firings, cone 9 has started bending before cone 8, contrary to the natural order. I mentioned it in the shop, and Jon and Linda said they'd seen it too. I noticed that the cone 8's are a new box, while the 9's are an early generation, probably inherited from another retiring potter. I wonder if Orton has changed the formula?

Doesn't really matter that much to me, as cone 10 is the goal. It's just unsettling to see my nicely organized line of cones fall out of sequence.

Last week was... challenging.

It's always stressful when we roll around into this time of year. Two big shows coming up, needing lots of work. Work that, as it happens, I'd already sold a lot of in August. There's also the issue of fitting in my committee responsibilities around the making and glazing of pots. I'm Graphics chair for both of the aforementioned shows, so have to save some energy and creativity--not to mention time--to design posters, postcards, ads and billboards. It's a lot.

But I felt for once I had a handle on things. I even finished the production run a little early, so I had a couple of extra days for the glazing. What could go wrong?

I first noticed something weird about my glaze the day I started glazing. There were some lumps of unmixed glaze, odd because I screened the whole works when I mixed up the new 20,000-gram batch in August. Didn't feel like getting my screen out, so I grabbed one in the kiln room and ran a bucket of glaze through it. And found a residue of speckled yellow sand in the screen.

This should not be there! Our raw materials are industrially processed, ground to powder and air-floated. Also, I'd screened the glazes once already. What the heck?

I briefly considered mixing an entire new batch of glaze, but we were out of one of the crucial materials, Zircopax--an opacifier, without which, my white glaze... isn't. So I started glazing.

When I got to the second bucket of glaze, I ran it through my usual screen with no residue, but it still felt weirdly gritty. Rescreening with the finer-mesh shop screen once again caught sand. I checked the bins of raw materials and didn't find anything amiss.

It wasn't until midweek, when I decided to fill up unused space in my last bisque firing by calcining more ball clay that I found the culprit. The top layer of the ball clay bin was a different color, yellowish, and when I rubbed some between my fingers, there was the grit. I scraped off as much as I could to get to the white clay at the bottom of the bin, and scooped out as clean a batch as I could.

I still couldn't mix up another batch, but realized I could maybe make do with Tin Oxide instead. It's much more expensive, but you only need half as much. I mixed up a 1000-gram test batch, glazed a bowl. Also glazed another in the suspect glaze, for comparison, took them home to fire to cone 9 in my electric kiln. The color would be wrong, but I could at least check whether things fused properly. At this point, I'd already glazed two-thirds of my bisque, and I was really hoping I wouldn't have to wash it off and start over. (Besides, there wouldn't be time--kiln is booked solid for the rest of the month.)

I spent all day Thursday either on the computer or catching up on errands while waiting, for the results. Of course, that would be the time my kiln errored out without reaching temperature. Twice. It's been taking longer on bisque firings lately, and using more power. Looks like it's time to replace the elements, but that's no help for me now.

One bit of good news, though--our order of Zircopax had finally come in, so I mixed up a 10,000-gram batch of glaze using the--hopefully--pure batch of calcined clay. I also dipped two more test bowls and fired them to cone 6 in the little test kiln at Club Mud, one with the new glaze, one the old. Glazed up my dinner plates, and a couple of special order pie plates. Washed off enough glazed pieces to redo the special orders, so at least those were likely to turn out. Went home around midnight and crashed.

Friday morning brought good news. Even three cones under-fired, both tests were smooth and vitreous. The suspect glaze had a lot of fine speckles, probably from iron in the sandy particles, but in reduction-fired stoneware, iron spots a feature, not a bug.

So I glazed all my remaining pots, the re-glazed orders, the soup bowls, toddlers, about half of the stew mugs and a few cat foods. Finished right at 5:30 pm.

What was going on? I suspect we had a donation of raw materials from a closing studio, and someone put fire clay in the ball clay bin, either mislabeled or through carelessness. I'm hoping that 8% of one clay is enough like another that it will all work out.

Fingers crossed.