Clay firing schedule

[larathompson288]

Hi there. 

 

I have two types of clay and I was wondering what the best firing schedule is for them for bisque? I have an electric Nabetherm kiln and I am making bowls/mugs. I don't really understand cones and so if possible, please explain using degrees C! 

 

Grogged Buff EarthenWare clay - Firing Temp.1000-1280deg.C

Stoneware Special Fleck Clay - 1120∞c - 1280∞c

 

Thank you !

 

[Sorcery]

I don't really understand C so please use cones if possible! JK!

Truth though, your clay doesn't understand C or F! Only cones!

Use the rightmost column since small cones are usually the only thing viewable thru an electric peep. And used in the sitter.

I'd call 1000C cone 07.

1120C cone 03.

1280C cone 8?

(I thought 1250C was cone 10, but that was all slow woodfired kilns.)

Kinda odd clays as far as temps, buff stoneware tends to be rather clean but "earthenware" (I've read UK terms differ from ours, though that temp doesn't) is rather dirty, which may mean a longer bisque time.

The other probably depends on what the flecks are.

Beastie Boys? Slo and Low that is the Tempo!

Sorce

 

 

[Min]

5 hours ago, larathompson288 said:

I have two types of clay and I was wondering what the best firing schedule is for them for bisque?

This can vary depending on how thick the pieces are but in general a slow bisque firing would be the safest until you get to know your kiln and firings. Temperature varies depending on how fast or slow you fire the kiln. Turning the kiln up quickly will take a higher final temperature to reach a specific cone rather than going very slowly to reach the same cone. In effect the cones are measuring both the time and the heat spent working on the clay. Temperature measures just that alone. 

Cone 04 (approx 1060C) is a common cone to fire to for functional work. It leaves the bisque strong enough to withstand being picked up with tongs and yet still porous enough to take up the glaze. Darker clay bodies can benefit from a slow rise in temperature through specific ranges. More on that here if you need it.

All that being said a cone 04 (approx 1060C) slow schedule for bone dry pots and using a programable controller below, this will take approx 13 hours.

- 26C hour up to 120C  no hold

- 90C hour up to 540C no hold

- 38C hour up to 590C no hold

- 80C hour up to 900C no hold

-27C hour up to 1060C no hold

If your pots are not bone dry then add a "candling" at the beginning. This is just holding at 90C for how ever long it takes to finish drying the pots. This schedule can be sped up but I'ld suggest trying this slow one first and see how your clay and glazes turn out. 

 

 

 

 

[Chilly]

On 1/10/2021 at 10:21 PM, larathompson288 said:

I don't really understand cones and so if possible, please explain using degrees C

The longer you work with clay and firing, the more you will understand that cones are king.

If you've ever done any cake making:  Imagine putting a fruit cake into a cold oven, and taking it out again when the oven gets to the correct temperature.  DegC = OK, cake = not OK.  Cake and clay both need heatwork.  An amount of heat for an amount of time.

Cones measure both.  Buy some cones and put them in your next firing.  Set 3 cones on every shelf.  1 cone for the temperature you're aiming for, 1 next hotter, 1 next lower.  And beware that the numbers start at 022, going up 021/020/019........ (getting hotter) to 01, then on up through 1 to 13.  Most use 04 for bisque and 06 or 6 or 10 for glaze.

 

I also use Special Fleck, bisque at 04, glazed at  06 and 6 in electric, and 8 in gas, and 12/13 in wood-firing.

 

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