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Hello! I am pretty new to ceramics but learning quickly now that I just hooked up my new/old/free kiln! Don't worry, I figured out all the electrical and have a vent and everything. My question is - I've never worked with stoneware, only earthenware. How much hotter do I need to fire, in general? Or do I?  I got some speckled stoneware clay to use for making coffee mugs. Thanks! 

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Your stoneware clay likely matures at a particular temp. If fired to a lower temp, it may not be fully fused (vitrified); if fired to a higher temp, it might just look toastier, however, also might weep little drops, fizz/bubble, melt, and/or other bad stuff.

I'm going cone five, as a few of the cone 5/6 clays I'm using misbehave if fired much hotter, and the ones that don't mind it are very well fused at cone 5.

Some clays are marketed as having a very broad firing range, however, I don't believe.

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Basically yes.

the general clays available would be lowfire, cone 04 range, mid fire cone 5-7, high fire, cone 10 ish. Porcelain is clay and you can get midfire and high fire formulations. In general, It is still just clay though.

The geology of the earth is cone 10 basically,  so clays are generally formulated or selected to fire lower for midfire or low fire.  This is a very general statement that explains why cone 10 is a thing on earth.

Bisque firing is intended to burn out organics and chemically bound water to make the ware sturdy and easy to decorate while leaving the clay in a porous state to accept glaze. Bisque firings generally go slow and depend on time at temperature to burn things out. Generally bisque firings run from from 9 to 12 hours. They are done first. Notice once all the chemically combined water is removed it will not go back to being clay. You can dowse it with water and unlike greenware it will not dissolve in your hand.

Glaze firings are done generally at the maturation temp of the clay to fully vitrify or mature the clay resulting in stronger clay and lower absorbency. Glaze firings can go pretty quickly and generally run from say 4- 10 hours. Glazes are made of the earths geology so they will even contain clay and have a maturation temp where they are fully fired or melted. Glazes melt as a result of composition where a basic glaze contains silica, alumina, a flux and often a colorant. Generally glazes and clay bodies of the same cone or maturation temp are used together to simplify things and allow one to fire both to their maturation temperature.

So yes mostly bisque to 04 range, and midfire clay and glaze  to cone 5-7 is the natural order.

Most cone 04 (lowfire) glazes and cone 5-7 (Midfire ) glazes have things added to a cone 10 glaze (basic geology of the earth thing) to make it melt earlier. One such component that was discovered as easy to use to lower the melting temperature is boron, so you may often hear that term.

I hope that helps, just reaching way back and thinking of all the stuff I wish someone told me from the very start a long time ago.

So in other  words,  in general you almost always have to bisque to the 04 range and then glaze fire to 5-7 range for midfire clays.

Edited by Bill Kielb
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yes, fire to cone 6 for strength.

bill an i hit the forum at the same time, he was faster.  reading his post makes me uneasy.  if you are a novice, i do not believe you should expect your glaze firing to cone 6 to be complete in only 4 to 8 hours.   the time depends on a lot of factors you have no control over.   i mention this because lately there have been several posts from people who thought their work was finished after a very short time and they were either turning off the kiln or wondering what was wrong.  they had unrealistic expectations from some source they believed.

you might contact the clay manufacturer for more info on your particular situation.

 

Edited by oldlady
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Yeah, somethin' like that!

Everything requires testing, and, as necessary, adjustment.

Some folk bisque a bit lower, as they want more porosity for applying glaze, whilst others may bisque a bit higher. For the clays I'm using, hitting a solid 04 is working well for me - I do like having a big longer "window" for glazing, for I'm still onna steepish learning curve, just over three years in.

Per prior, I'm having better luck for glaze fire at solid 5, down from pushing cone 6 all the over - too hot. Expect to test, then adjust as necessary.

If you haven't yet found Tony Hansen's website, here's an article on vitrification

https://digitalfire.com/glossary/vitrification

...scroll down a bit to "The best firing temperature for this body?

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37 minutes ago, oldlady said:

i do not believe you should expect your glaze firing to cone 6 to be complete in only 4 to 8 hours

I will change that to say 4-10 hours which is generally accurate. Glaze firing is typically done 400- 570 degrees per hour and bisque in the 200 degree per hour range. The point I was trying to make is for bisque time at temperature is essential and as a result generally needs to be longer than the glaze firing. . An explanation of how to successfully cone fire is a whole other discussion about heatwork and where fluxes begin to help things melt.

Edited by Bill Kielb
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Thanks so much for these helpful responses! I do realize that there is some range in both the bisque and glaze firings, I was just trying to get a general understanding of the differences between the different types of clay. I have done some research and am feeling much more informed. It looks like there are a lot of other conversations on this forum to will be helpful too. Glad I joined! 

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