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Difference In Digital And Manual Kilns

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I asked about firing clay at a higher temp. I wrote the Standard Clay Company before posting here. They finally got back with me. 

Here was my question:

I recently bought 266 DARK BROWN CLAY (Cone 4-6) I was wondering if it can be fired at cone 8?

I am firing 308 Brooklyn Red to cone 8 to get the darker color and want to fire both clays together in the kiln. But I don't want to ruin my pieces if it can't be fired that high.

 

Here is their respnse:

No the 266 clay works best at a cone 5 firing. If you fire it too high the pieces will bloat. I suggest you fire all you 266 to a cone 5 on a programmable kiln with a 10 min hold, or to a witness cone 6 at 3 o’clock.

 

Julie Hregdovic

Standard Ceramic Supply

Chem-Clay Corp.

24 Chestnut Street

Carnegie Pa 15106

 

My question is, why the different cone # for a programmable kiln vs witness cones.  I am assuming the witness cone # is for manual kilns.  Or am I mistaken?

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I would guess, that they equal the same amount of heat work. Since you can't do a hold, once you reached a certain cone, with a manual or kiln sitter, you just use the next cone higher as a gauge. They said go until the cone is at 3 O'clock, so it hasn't fully reached cone 6. So both will equal a cone 5 and quarter to a third or so.

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CALL the number for standard clay and ask Julie what she means.  i think she means that with a manual kiln you should use a large #6 cone that is visible through the peephole and let it fall to the position that the number 3 is on a clock.  talk to the expert each time you can.  it is faster and more useful so you can follow up with additional questions and get answers right away, not wait days for someone here.

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That witness cone is a Large cone for peep hole "manual kiln"... If you fire a small cone 6 to 3 oclock you just hit cone 6.

...

 

If you have a manual kiln, just pop a small cone 5 in and your good as long as its set properly..

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My kiln is actually new. It's an L&L digital.  I've had a Duncan for about 15 years before it quit, it was manual.   I was just confused about the cone thing.  Cause the clay says 4-6 cone but Standard recommends to fire at 5.  I usually fire most things at 5 for glaze recommendations.  But on occasion,  I'll make something that is not glazed and want to fire higher to get the darker color.

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My kiln is actually new. It's an L&L digital.  I've had a Duncan for about 15 years before it quit, it was manual.   I was just confused about the cone thing.  Cause the clay says 4-6 cone but Standard recommends to fire at 5.  I usually fire most things at 5 for glaze recommendations.  But on occasion,  I'll make something that is not glazed and want to fire higher to get the darker color.

 

Cone 5 with a 10 minute hold will get you to 5 1/2. With a manual kiln there's no cone 5 1/2 to put in the sitter, so you have to fire until visual cone 6 is bent to 3 o'clock, which equals about 5 1/2. Visual (large) cones start at about 1 o'clock, and you've reached the cone when they are bent all the way to the shelf, or 6 o'clock.

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if they recommend ^5 i would stick to it... i had a problem with a website saying one thing and the box said a different.. the website was wrong so i did what the clay co. said to fire it at...

 

if you want to try and understand the risk, you may be able to test a piece in a bowl to ^6 just to see for yourself..

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My kiln is actually new. It's an L&L digital.  I've had a Duncan for about 15 years before it quit, it was manual.   I was just confused about the cone thing.  Cause the clay says 4-6 cone but Standard recommends to fire at 5.  I usually fire most things at 5 for glaze recommendations.  But on occasion,  I'll make something that is not glazed and want to fire higher to get the darker color.

 

Cone 5 with a 10 minute hold will get you to 5 1/2. With a manual kiln there's no cone 5 1/2 to put in the sitter, so you have to fire until visual cone 6 is bent to 3 o'clock, which equals about 5 1/2. Visual (large) cones start at about 1 o'clock, and you've reached the cone when they are bent all the way to the shelf, or 6 o'clock.

 

Orton does make a cone 5 1/2 for sitters, but not all suppliers carry it.

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if they recommend ^5 i would stick to it... i had a problem with a website saying one thing and the box said a different.. the website was wrong so i did what the clay co. said to fire it at...

 

if you want to try and understand the risk, you may be able to test a piece in a bowl to ^6 just to see for yourself..

 

Ummmm .... I'll pass on that ... lol  I understand more now about the cone difference.  I like working with different clays and mixing them together.  Mostly they are all different cones.  I've always fired at the clay's lowest cone which is 5.  So I'll just fire all the Standard 266 at 5 and fire the 308 separately at 8. 

This has been very educational for me.  And you all saved my work from disfigured.  Thank you :)

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Hey folks, part of your answer is already answered. If you check the Orton cone chart you will find that at a rate of climb of 108F./hr is 2232 for a ^6 cone. Check that against a small ^5 and that is 2230. So you could fire a kiln at moderate climb and get cone 6 equal to cone 5. At the same time, they call for a ramped firing(10 min hold).

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All the answers to this are good,  One comment is that the kiln sitter was meant as a safety device for manual kilns.  Somewhere along the line people started to use them to shut off the kiln without using witness cones, which also could cause overfiring problems.  So on manual kilns a witness cone is what you should use to determine when to shut off a kiln. Small cones were made for the kiln sitter.  Most kilns now use a programmer but again witness cones should be in the kiln.to be sure the temperature and heat work were reached.  A 10 min hold for cone 5 will amount to about 14 deg F increase in heat work if the ramp was 108 deg F for at least the last 90 min of firing.

David

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