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Atmosphere Kiln

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I am trying to understand firing with a living fire as opposed to just heat. Talking broadly here. Wood and gas including soda vs electric. Not including other firings like pit, raku...

 

Even with the different kind of atmospheric firing are there some principles that are common to all atmospheric firing like how you get flashings if you have the right kind of clay/ slip? Would there be flashings In both wood or gas. I keep coming across flashings in soda firing and wood of course, but I don't hear the same when it's just a gas firing.

 

I am curious what flame does to a body - glazed/ unglazed. I understand I've opened Pandora's Box. I understand there are so many intricacies to even each kind of firing.

 

It's the flame that interests me. Including the flame that Native Americans use since I assume flame because they are not using sawdust.

 

Is there a difference between natural gas and propane flame? Difference between firing with wood vs firing with charcoal. Could I fire a pot in my charcoal BBQ or propane BBQ. seems would be like a pit firing.

 

What do I get with flame and air that is different than electric firing. Beyond color change. Beyond reduction.

 

Sorry if I don't make sense. I keep thinking of cooking analogies here. They still apply.

 

I am slowly getting to understand heat work - kinda. How it's different for a bowl vs a vase no matter what the firing.

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Flashing happens in soda and salt kilns because there is some fluxing of the surface of the clay. In wood firings, small amounts of melted ash have the same effect, and the vapor from the burning wood has a similar effect to soda & salt, although it is not nearly as strong. It's all about the reaction of sodium, potassium, silica and alumina, with reduction and cooling. In all cases, too much fluxing and it all just glazes over and you lose the flashing. It all has to do with small amounts of iron at the surface.

 

In a basic natural gas or propane firing you don't have the vapor, so things don't flash unless they've been formulated to flash without the vapor, like shino glazes.

 

Pit firings are all about trapping vapors, carbon, etc. into the porous clay. It can have a somewhat similar organic look to the high firing processes, but it's a different mechanism at work.

 

This is a terribly simplified explanation.

LeeU, Chilly, douglas and 1 other like this

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excellent , Neil!

As for NA pottery, they use cow dung for fuel.At last San Ildefonso potters did.  There are hot spots and passages for the flame.

Horse turds add some spice to the fuel creating a black with sheen. Higher nitrogen. Sawdust or ash was put on top after the flame burned through to the top. Maria Martinez used old sheet metal or license plates to encase the smoldering and give her the black reduction.

 

 

Marcia

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