John Post

I have a couple of computer controlled kilns I use in my studio and at school. In order to get the tomato red glazes and the other red glazes on this site to work in your kiln, you will need to slow cool the kiln. I use the firing profiles below with the glazes on this site.

 

Cone 6 slow cool profile

Fire at 200° F per hour up to cone 6
Let the kiln cool on its own down to 1800° F
Then slow cool at 150° per hour down to 1300° F
When the kiln reaches 1300° F, I let it cool down on its own from there

 

Normal bisque profile

This profile is used for bone dry pots of normal thickness.
90° F per hour up to 185° F
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own

 

Damp ware bisque profile

This profile is used for pots that are past leather hard but are not bone dry
90° F per hour up to 185° F
hold at 185° F for 4 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own

 

Thick as a brick bisque profile

This profile is used for sculptures or kid made wares that are thick as a brick and would explode from the steam in a normal firing
90° F per hour up to 185° F
hold at 185° F for 8 hours
100° F per hour up to 600° F
200° F per hour up to 1922° F
Let the kiln cool on its own

 

Majolica Cone 1 profile

I use this profile with a cone 1 white glaze over the top of earthenware terra cotta. Then I paint Amaco cone 05 and 06 glazes over the top. Amazingly they don't run off at cone 1.
Fire at 200° F per hour up to cone 1 (2109° F in my kiln)
Then let the kiln cool on its own
This one is barely a profile but it works.

 

(F = Fahrenheit in all of the above profiles)

 

Troubleshooting iron red glazes...

I've received a fair number of e-mails from potters asking me why their attempts to reproduce my iron red glazes did not work for them. Often they tell me that their glazes turned brown instead of the reddish colors they see on my pots. The following are the things I have done to get iron reds to fire consistently red in my electric kilns. These are all of the tips I have and the only way for you to get iron reds in your kiln is for you to apply these principles.

 

Make Sure you Slow Cool your Kiln

Iron reds form as the glaze cools. I cool at 150° Fahrenheit per hour from 1800° to 1300°. Try a cooling at 125° per hour or 100° per hour if you are having trouble getting reds. Or program in a hold somewhere between 1800° and 1700° and see what happens. The only way to get my glazes to work in your kiln is to do some of the legwork for yourself. Try different firing profiles than mine if my schedule is not giving you the results you want.

 

Slow Cooling with a Kiln Sitter

After your kiln sitter drops, lift the latch slowly and press the plunger button back in. Then slowly lower the latch so that it does not trip the switch and shut off the kiln again. On kilns that have low-medium-high switches, try setting the kiln on medium for a few hours. On kilns that have a series of simple on-off switches, turn half of them off. On the manual kilns I have worked with, these strategies have created a slow cool. After a few hours of slow cooling, turn your kiln off. If your kiln looks orangey inside it is in the 1600-1800° range and that is the where iron red glazes need to spend some time.

 

Try a line blend

The quicker a kiln cools, the more iron a glaze needs to precipitate to the surface to create an iron red. To find out how much iron you need in your glazes, create a line blend with 0% iron red at one end, and 20% iron red at the other. I do a 10 part blend so that the glazes I get from it contain iron in amounts that increase by 2% from 0 up to 20. In my kilns with my firing schedules, I find that I get the best iron reds in the 8-12% iron range, but your kiln might fire differently than mine. Creating a line blend will help you dial in on how much iron you need in your iron red glazes.

 

Try different types of iron oxides

I have used Spanish iron oxide, refined red iron oxide, black iron oxide, yellow iron oxide and some wet concrete colorants from Home Depot and have achieved nice iron reds and Jen's Juicy Fruit glazes with all of them. Some potters feel strongly that the type of iron you use has a big influence on whether or not you get a nice iron red glaze. I haven't found this to be the case in my kilns. I think using line blends and finding the sweet spot in terms of the amount of iron in your glaze and working with different cooling cycles is more likely to get you moving in the right direction. But if you are still struggling and want to try something, you could try different types of iron oxides.

 

Clay Body Choice is Important

Different clay bodies react differently to iron red glazes. I get good results on Tuckers Mid-White clay body and on Rovin's RO-10 Stoneware body. Try the different clay bodies that you currently use before switching to a new one. Do line blends and vary the cooling cycles. These procedures might help you dial in on an iron red glaze and firing process that will work in your kiln.

 

Patience and a Willingness to Experiment

That's it in a nutshell. I can't fix your iron red problems in an email. The procedures above are what I used to get things dialed in with the clays I use and the kilns I fire them in. You'll have to go on the same journey to get them to work in your kiln.

 

 

Iron Red Glazes at Cone 10 Electric Oxidation

Conor McLean is an apprentice to Dan Weaver at WaterStone Sinks. He is working with Dan developing Iron Red Glazes at Cone 10 in electric kilns. You can visit Conor's blog to view his progress.