Stephen Hill Firing Schedule

[docweathers]

One unique feature of Stephen Hill's firing schedule is that he goes to someplace in ^ 5 then holds for up to an hour until the ^ 6 drops.  what is the point of this versus simply going to cone 6?

[Babs]

Non expert here but I do this because it allows the glaze to mellow and mature. Any  pinholes, bubbles etc tend to dissipate and the glaze sttles to the pot.  Some pinholes caused by a poor bisque technique may not forgive. Driplines soften.

I think the reason that this occurs is because of the heatwork done as opposed to the Cone reached. The cone6 touches its toes but the ware has had heat working on it over a longer period of time.

May be more economical?

[neilestrick]

It does save wear on elements to fire to a lower temperature. Glazes can look radically different when held at temperature to achieve heatwork, although some glazes will not melt the same. I once soaked from 4 to 6 and a couple of my glazes came out underfired. Others had their color altered in a way that was not attractive. Others looked good.

 

You'll have to test with cones to see just how long the hold needs to be. I used to fire cone 8 by going to 6 plus a 40 minute hold. But to soak from 4 to 6 required an 80 minute hold.

 

I get better results from a slower cooling rather than a soak going up.

[docweathers]

I certainly agree with all of the above. it seems curious to me that he is the only one of the big-name potters, that I'm aware of, that does a conspicuous soak at the top.

[Babs]

I think maybe it is an unspoken practice. ?? Pos. more so in the days of manual sitters. Only my thoughts.

[clay lover]

I do a 40 min soak to get the temp more even throughout the kiln.    The ramp for the last 200* is 100*/hour. both things seem to help evenness.

[Pres]

Once ^5 starts going down I turn the kiln down until ^6 is at 90. I let the kiln cool for to red orange, then turn low on til it no longer glows. Then off.

[docweathers]

Babs

 I think you're right that a lot of other famous potters do a hold at the top.  I'm glad to see them speaking up here

[Hanoverian]

Neil - could you please expound on your slower cooling schedule?
"I get better results from a slower cooling rather than a soak going up."

Also.. I'm not very familiar with how glaze ingredients are effected by soak vs higher temp. 
You mentioned that some glazes didn't mature or had altered color.
Did you find specific types of glazes or certain glaze ingredients that didn't do well with the soak technique?

Any info is greatly appreciated!
KB
Portland, OR

[Biglou13]

Neil can you expound on holding schedule.like 6 to 9. 7-9

Etc. please

[Biglou13]

It does save wear on elements to fire to a lower temperature. Glazes can look radically different when held at temperature to.............

 

You'll have to test with cones to see just how long the hold needs to be. I used to fire cone 8 by going to 6 plus a 40 minute hold. But to soak from 4 to 6 required an 80 minute hold.

 

I get better results from a slower cooling rather than a soak going up.

Neil if I wanted cone 9. From a cone 6 or 7 kiln temp. How long would I need to hold at temp to get the 9 cone to drop? I know I need to test . But a ball park would help. Is there a formula to figure this out?

[neilestrick]

In my very limited experience with soaking to drop more than one cone, it seems to vary depending on which cones you're working with. 6 to 8 took me 40 minutes. 4 to 6 took 80 minutes. It may also have to do with the speed of firing up to that point. I haven't done any further test to try and figure out all the details. I would imagine going from 6 to 9 would take at least an hour. The only way to do it is to test. Put some large cones in the kiln, fire to whatever cone with a hold of at least 2 hours to be safe. Watch the cones drop and see how long it takes.

 

As for my glazes, I would say those that have a narrower firing range were definitely the most negatively affected by soaking rather than firing up. Specifically, they came out under fired. I think their makeup is such that they need to reach certain temperature in order to begin melting, rather than an amount of heat work, if that makes any sense. As we've been discovering, not all things in the kiln respond to heat work in the same way. I think that sometimes you just have to get hotter for it to work.

 

I fire to cone 6, and cool my kilns at a rate of 175F per hour down to 1550F. Technically they say you should go down to 1450 or 1400, at which point slow cooling won't have any effect, but I don't see any difference at 1550. The whole cooling cycle takes less than 4 hours, and is only slightly slower than my big kiln cools anyway. Mostly it just slows it down at the top end. When I slow cool, all of my glazes look better. The glossy glazes are glossier and have deeper colors, and the matte glazes have more crystal growth, giving much more depth and variation.