Electric Kiln Slow Cooling Program

[Dave K]

I have an electric kiln and use commercial glazes. I use a firing program that goes to 2160 with a 5 minute hold, then at a rate of 125 per hour cools to 1900 and holds for 30 minutes, and cools naturally the rest of the way. This works fine but I am always looking for a way to improve my glaze results. I have a books on cone 5/6 glazes that tested a glaze with 7 different cooling programs. One cools naturally to 1750,then at 50 per hour to1600,holds for an hour then still at 50 to 1500, and naturally the rest of the way.

 

My question is can I add the hour hold at 1600 to what I am already using without causing problems? Does anyone see a benefit to doing this or am I kidding myself?

[Joseph Fireborn]

You can add a hold at 1600 with no problems, as far as what it will do to your glazes only testing will tell as you don't know what ingredients are in the commercial glazes. There is a good chance it wont do much, but there is always a chance it will be amazing and blow your mind! You never know unless you test.

[Min]

If you are using iron red glaze(s) then the cool down rate has a huge part in how the glaze will look. If they are reactive glazes, mottled, hares fur etc then the slow cool hold will also likely have an effect, same for matte glazes. For clear gloss glazes adding that 1 hour soak at 1600 I don't think will make much difference.

 

Good article on slow cooled iron reds here http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/the-many-faces-of-iron-an-exploration-in-cooling/

[neilestrick]

Test, test, test.... I don't see much difference in my glazes at all below 1600F, but yours may love it.

[Dave K]

Thanks for the replies. I think I will give it a try and see what happens.

[Joseph Fireborn]

Thanks for the replies. I think I will give it a try and see what happens.

 

Good decision, because if nothing really special happens, you don't have to wonder what would happen anymore, and can focus on the next thing.

[docweathers]

I've read a lot about the virtues of slow cooling glazes. I've never heard anything about the downside of slow cooling. 

 

Is there any class of  ^6 glazes or glaze materials that doesn't respond well to slow cooling? if yes, what sorts of bad things happen to what kinds of glazes or materials?

 

How far is it useful to push slow cooling or long holds at higher temperatures? Stephen Hills seems to favor long holds and slow cooling and gets wonderful results.

I mix my own glaze,  so I know what's in them.

[Babs]

One of my glazes goes too matte for my liking.

[Joseph Fireborn]

Some glazes get too soft with a super slow cool. They turn into a textured surface that feels really sandy, but isn't sandy. It is hard to describe. Also some of my glazes with iron in them are nice and colorful without a slow cool, add a slowcool and they turn brown. I find a mix between super slow and super fast is best. Somewhere in the middle.

 

Stephen works with glazes that all want to be slow cooled on top of Strontium Crystal Magic(SCM) which is how he gets those interesting surfaces. That glaze contains a lot of titanium which is a crystal former and a variation creator. So the combination of those two creates some pretty wild surfaces. I don't particularly like how the glazes feel with that schedule, you have to be very careful not to add to much SCM or it just makes the surface horrible to touch for functional work imo. If you can spray it just perfect though you get some amazing surfaces. I am still working on it right now. I don't use SCM, but I do use another glaze with titanium in it as a layering glaze and I am using a modified version of Stephan hills firing schedule. 

 

This was a bowl I pulled out a while ago, the most successful of my attempts to date. I haven't been able to replicate it exactly as good as this one, I am still trying to do it every firing, I get close, but nothing as nice as this one. The crystals around the rim are the part that I am after. I find them to be so beautiful and wonderful to look at. I really love surface changes on my pots. going from matte to glossy, or thick glazes to thing glazes or bare clay then back and forth.

 

 

This was with a modified version of Stephen Hills schedule.

 

If your happy with your glazes then I wouldn't change anything. I am super picky and I really want my work to be in a certain place, so I am at the phase where I experiment on 50% of the pots in my kiln, and I try to sell the other 50% with non experimental stuff to pay for materials. Ideally I would like to have a test kiln that I could fire every night, but it isn't in the budget right now, so I am slower than I would like to be.

 

I only want to work with one set of glazes, but I haven't found that set of glazes yet, nor a schedule that I like with the glazes I want to work with. So I am always testing every time I fire. It is frustrating and exciting at the same time. Just make sure if you do test glazes overlapping and different things, make really good notes. There is nothing more frustrating then opening your kiln and pulling out a pot and being like, I LOVE THIS. Then failing to remember what you did and never being able to replicate it again, I have done this several times. 

[fergusonjeff]

There are definitely some cone 6 glazes that are less interesting with a slow cool.  I was really excited to try it a few months ago and found that my VanGilder Waxy white was great with a slow cool, but most of my runny-swirly-rutile layered glazes were ruined.  Rather than having swirls of color that looked like flowing glass they all blended into slightly matte single colors.  A slight hold at peak temp gets them moving and then a crash cool freezes them in action.  A slow cool allows everything to blend together.  Aside from an occasional load of matte white I don't intend to do any more slow cooling with my usual glazes.

[neilestrick]

Some of my glazes look better with a slow cool- more crystal growth, interesting surfaces. Some will get too matte if I cool too slowly. One of the main reasons I started to slow cool is that my kilns are radically different sizes, and by doing a controlled cooling cycle I can get the same results out of all 3 kilns. Otherwise my test kiln cools in 8 hours, my middle kiln cools in 16 hours and my big kiln cools in 30 hours. I do a controlled cool of 175/hr from cone 6 down to 1550, which isn't much slower than the big kiln cools on its own. One of the benefits of cooling from the peak temperature is that my glazes get to spend a little more time at high heat, which some of them really seem to like- brighter colors, glossier surface.