[Clayart] Down firing

Hank Murrow via Clayart clayart at lists.clayartworld.com
Fri Jul 24 12:10:03 EDT 2015

On Jul 23, 2015, at 7:40 PM, Gina Mars via Clayart <clayart at lists.clayartworld.com> wrote:

> Hi,
> I was wondering if anyone including Mel can go over the down firing technique that he did firing his kiln yesterday. 

Dear Gina;

I assume that you are firing a gas kiln as I do; but the technique can be used in other fires with good results. 

After firing down with a bunch of draw trials, pulling one every 50F during the cooling cycle, I determined from that experiment that the micro-crystals develop between 1900 and 1800F. So I cool from C/10 with the damper shut until 1900F, and then fire up the kiln again at around 2" wc gas pressure(from 6" full on) in full oxidation(no back pressure at the upper spyhole); and hold that steady oxidizing condition for anywhere from 2 to 8 hours, depending on how strongly I want to affect the glazes. After this soaking period, I cool the kiln normally, or somewhat faster than normal.

The main changes you may see are: 1. more micro-crystalline development.
						 2. deeper color development.
						 3. fewer to no pinholes.
						 4. a higher success rate than before.

You will need a thermocouple and meter of some kind to read temperatures once the cones have fallen. I use an OxyProbe for its ability to measure the atmosphere as well as its excellent Platinum/Rhodium thermocouple, which is accurate at all temperatures up to, and beyond C/10.

I fire mostly in my Doorless Fiberkiln design as seen here:  http://www.murrow.biz/hank/kiln-and-tools.htm   you can see the meter hanging on the support-mast at left.

This general technique has been confirmed by many Clayart members in electric, gas, oil, and wood kilns. I wish you luck with it.

Cheers, Hank in Eugene

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