The Great Carbon Trap Research Project - 2
I learned a lot of lessons from the first attempt at testing my assortment of carbon trap shinos. "Surely, this next time I'll get it right!" I thought.
I did not.
But I did learn a lot (again!) from this firing... and I do think that next time I'll get it (maybe? is it hubris to think that??).
So what happened? What went wrong? What went right?
A lot went right actually. Definite progress has been made. For example, I have found the perfect spot to dry my glazed-cups in the studio. In the Fish Bowl (as some of us affectionately call it), where the second-year students and masters students have their desk space, it is very dry and warm compared to the rest of the studio. Besides the office, it's the smallest room we have and it uses side radiator-like panel heaters rather than the over-head heaters the bigger rooms have (which only sometimes work it seems). This means I don't have to let the cups dry for a week or more to get proper soda ash coverage. Here's a pic of one of the cups a day and a half after glazing:
You can see that crusty white stuff forming on the outside of the glaze. That's the soda ash coming to the surface. You can also see on the raw clay body where it's a bit more orangey - this is also where the soda ash has absorbed into the bisced clay. I had glazed this batch on a Friday morning, and taken the above photo Saturday evening. By Tuesday morning when I went to fire them, this cup was completely covered white!
So things are certainly looking up! However this is where I mess up (again). I (foolishly!) put the cups on the bottom shelf. A little background on the kiln I fire these in: this is a big gas kiln. I don't have the measurements off hand (I'm at home while I write, not in the studio), but it's quite sizable. Over the past year, Rob and I have had to do some adjustments to it to get the reduction working properly. There was a bit of time mid-to-late last year where only the very top of the kiln was going into reduction. We cleaned out the burners and had a gas guy come and adjust the pipes a bit. After that it was almost too-easy to go into very heavy reduction and a successful, well-reduced-throughout firing would take around 5-6 hours.
As more firings have gone one though, it's seeming like it's reverting to its old ways. I now have to keep the damper quite shut throughout the firing to get heavy reduction, and even then the bottom shelf is not getting hot enough nor is it reducing as heavily as the rest of the kiln. The firing for this batch took eight hours, and then it wound up not even having put the cone 10 over fully!
As you can maybe see in the above image, the cone I had on the bottom shelf (a cone 10), didn't even start going over. So these shinos are all underfired! However, they did get some reduction. I think they didn't get a heavy enough reduction at the proper temperature, combined with not getting hot enough overall, which led to yet another disappointing result.
On the bright side, some of them do show signs of carbon trapping finally! You can maybe see in the above group shot how some of them have a more greyish, almost lavender appearance. This is due to the shadowy carbon being trapped in the surface of the glaze. In addition, some of them did some much more characteristically-shino things like crawling and breaking to a bright red where thin and between the crawled bits of glaze (especially on the Whitestone cups, which I included in this test).
Above are some of my favorite results from this batch, ones that I think are most promising going forward.
So what will I do next time?
Place the shinos higher up in the kiln
Fire for even longer, even if that means a 9-10 hour firing to ensure it is hot enough and reduced enough
Dry the shinos in the same place in the Fish Bowl