Questions about slow cooling and kiln temps

[SunsetBay]

One of the reasons I replaced my old manual kiln was that I wanted to experiment with slow cooling. But my new L&L kiln with 3" bricks cools so slowly on its own, I'm wondering what advantage there would be, if any, to programming a slow cool. I don't produce enough fast enough to do a lot of experimenting with the kiln, unless firing an almost-empty kiln is acceptable. Which I always thought was not ideal, for a variety of reasons.

I've tried both the pre-programmed medium and slow glaze-fire programs, and haven't seen a significant difference in results. 

Also, based on witness cones, the top shelf is not getting as hot as the rest of the kiln--I'm assuming this is due to the open peephole at the top. The difference can be as much as half a cone (if that description makes any sense). Is there something I should/can be doing to "fix" that? Change the TC offset on the top thermocouple? Something else?

At the moment, I can't work with clay as I am dealing with a painful case of trigger thumb. I have 3 more weeks to wait before my appointment with the hand doc, so I'm getting lost in the rabbit hole of thinking about pottery, learning and planning. I'll probably be here with questions a lot!

[neilestrick]

A slow cooling program will cool slower than the kiln can naturally. The slower cooling can give some glazes a chance for more crystal growth, which can make the glaze look more interesting. It all depends on the formula of the glaze as to how the slow cooling will affect it. Some glazes don't look any different at all, some change dramatically. It's worth trying. You can either cool from the peak temperature, or crash cool to 1900F, then do a controlled cooling down to 1450F. I'd start with a cooling rate of 150F/hr and go from there. If you really want to pursue glaze testing, a little baby test kiln may be worth the money.

If the top section of your kiln is uneven at all temperatures, then adjust the thermocouple offset to even it out. If it's only uneven in your glaze firings, then do a cone offset to fix it.

[SunsetBay]

7 hours ago, neilestrick said:

A slow cooling program will cool slower than the kiln can naturally. The slower cooling can give some glazes a chance for more crystal growth, which can make the glaze look more interesting. It all depends on the formula of the glaze as to how the slow cooling will affect it. Some glazes don't look any different at all, some change dramatically. It's worth trying. You can either cool from the peak temperature, or crash cool to 1900F, then do a controlled cooling down to 1450F. I'd start with a cooling rate of 150F/hr and go from there. If you really want to pursue glaze testing, a little baby test kiln may be worth the money.

If the top section of your kiln is uneven at all temperatures, then adjust the thermocouple offset to even it out. If it's only uneven in your glaze firings, then do a cone offset to fix it.

Thanks, Neil. I'm not sure I have enough patience or determination for a level of commitment that would warrant spending the money on a test kiln...not yet, anyway. I'm thinking I will continue by including test tiles in my regular glaze firings, and maybe stick with the programmed glaze schedule until I see where I might want to change things by slow cooling. Not sure yet. I get over-eager sometimes and want to rush to results, which I know isn't the best way. 

The top section of the kiln seems cooler at all temperatures.  I guess I'll have to remember how the thermocouple offsets work and experiment with that (in small increments. First I have to figure out which physical thermocouple is attached to which one in the controller; presumably, I can see that on the original diagram I used to wire it all up when I got the kiln. Then I'll go from there.

Thanks again.

[Mark C.]

With a zone controller -there is no reason for cold spots after some tinkering as Neil said.

Also never hurry results-never good outcomes

[neilestrick]

@SunsetBay First make sure your thermocouples are touching the ends of the protection tubes. Just loosen the screws that hold the TC in the porcelain block, push the TC in until it touches the end of the tube, and retighten the screws. If all seems well there, go ahead and adjust the TC offset. Instructions here: http://hotkilns.com/thermocouple-cone-offset

[SunsetBay]

On 11/12/2018 at 8:30 PM, neilestrick said:

@SunsetBay First make sure your thermocouples are touching the ends of the protection tubes. Just loosen the screws that hold the TC in the porcelain block, push the TC in until it touches the end of the tube, and retighten the screws. If all seems well there, go ahead and adjust the TC offset. Instructions here: http://hotkilns.com/thermocouple-cone-offset

Thanks. I've adjusted the thermocouple offsets before--back when I first got the kiln (about 2 years ago)--with help from  Rob Battey, whom L&L connected me to at the time.  I will check the actual thermocouples in their tubes now.