Kiln toxicity

[Iforgot]

Hey World,

I am doing a ^10 firing and I plan on spraying my pots with Spodumene suspended in water before firing. I was wondering if I should take any special safety precautions while firing. Thank you!!!

[Marcia Selsor]

Your kiln should be in a vented area. I don't know specifics on spodumene but it is probably wiser to not breathe any kiln fumes.

This should also be a consideration for those who like to cook with the excess heat. Consider the fumes off gasing if you think it

is a good place to roast hot dogs.

Marcia

[OffCenter]

Hey World,

I am doing a ^10 firing and I plan on spraying my pots with Spodumene suspended in water before firing. I was wondering if I should take any special safety precautions while firing. Thank you!!!

 

 

Why are you spraying your pots with spodumene?

 

Jim

[Guest JBaymore]

Hey World,

I am doing a ^10 firing and I plan on spraying my pots with Spodumene suspended in water before firing. I was wondering if I should take any special safety precautions while firing. Thank you!!!

 

 

Why are you spraying your pots with spodumene?

 

Jim

 

 

 

 

My question also.

 

best,

 

.....................john

[Marcia Selsor]

I wondered that too.

Marcia

[TJR]

Man;

You guys are smart! My question also. I know Spodumene is a glaze material, but I can't recall what it does in the glaze exactly.Could it be for making a sheen on the pots/sculpture? I have never heard of this procedure.

Tom[TJR]

[Guest JBaymore]

Spodumene is a lithium fluxed "feldspathoid" .... at least for all general intents and purposes ot can be looked at as that in this case.

 

The lithium content can tend to be slightly volatile at cone 10 range and will SLIGHTLY fume surrounding clay.... but other materials do this far better. it melts slightly at cone 10.... but true feldspars do this better too.

 

best,

 

.......................john

[LilyT]

Marcia, since you bring up the off gassing issues... Do you think it's

safer to use the heat on the way DOWN from a firing? No one needs

to cook at 2450F anyway, and our pottery can generally be used

in ovens and even at stovetop temperatures in the house.

 

I was thinking about making a little baby oven on the roof of my

woodfire kiln and using it either for casseroles or meats in sealed

crocks or baking when the temperature is a lot more reasonable.

 

Anyone else who has an opinion should give it, too :-).

 

And I entirely second (fifth? sixth?) the opinion that all kilns should

be outdoors or vented, whether or not spodumene is used. Am I'm

also curious as to the reason to spray spodumene onto the surface.

Give us a clue :-) - enquiring minds want to know more!

 

-Lily

[Marcia Selsor]

Lil,

I would just stay away from cooking and kiln exhaust. Many years ago there were designs for channeling kiln heat in heat exchangers, but there was not cooking. Maybe if one used radiant heat sealed from exhaust fumes, it might not be a hazard.

I have used spodumene as a feldspadic flux as John mentions, but I have never used it as a wash. Maybe it would give a similar results as colemanite (Gerstley Borate is the contemporary substitute for Colemante) washes as used by Voulkos. I can't say, since I have never tried it.

Marcia

[TJR]

Spray Gerstely Borate on instead.

On the subject of cooking with wood-kilns;

Build a box of hard brick about 3 ft long by 2 ft wide. Shovel in some coals and embers from the fire box. Bury your casserole. You can also put a piece of boiler plate[ thick metal sheet 1/2 inch thick] on top of your box. On this you cook hamburgers and hot dogs. The fire box of your kiln would be WAY too hot to cook anything.

TJR.

[TJR]

Spodumene is a lithium fluxed "feldspathoid" .... at least for all general intents and purposes ot can be looked at as that in this case.

 

The lithium content can tend to be slightly volatile at cone 10 range and will SLIGHTLY fume surrounding clay.... but other materials do this far better. it melts slightly at cone 10.... but true feldspars do this better too.

 

best,

 

.......................john

 

 

John;

Did you look this up in a ceramic reference book, or was this rattling around in your brain? I am impressed!

TJR.

[Marcia Selsor]

Spray Gerstely Borate on instead.

On the subject of cooking with wood-kilns;

Build a box of hard brick about 3 ft long by 2 ft wide. Shovel in some coals and embers from the fire box. Bury your casserole. You can also put a piece of boiler plate[ thick metal sheet 1/2 inch thick] on top of your box. On this you cook hamburgers and hot dogs. The fire box of your kiln would be WAY too hot to cook anything.

TJR.

 

we cooked breakfast on the intake side of the firebox in an extension of bricks with a grill on top of that when I was in Washington. I felt ok with that. The exhaust is what would concern me but the draft was pulling away from the food. Pizzas were cooked in a separate pizza oven. Several roasted dishes were also cooked in the pizza oven.

 

Marcia

 

 

[Guest JBaymore]

Spodumene is a lithium fluxed "feldspathoid" .... at least for all general intents and purposes ot can be looked at as that in this case.

 

The lithium content can tend to be slightly volatile at cone 10 range and will SLIGHTLY fume surrounding clay.... but other materials do this far better. it melts slightly at cone 10.... but true feldspars do this better too.

 

best,

 

.......................john

 

 

John;

Did you look this up in a ceramic reference book, or was this rattling around in your brain? I am impressed!

TJR.

 

 

 

 

TJR,

 

Rattling around in the brain. I've been teaching ceramic materials science since the mid- 70's. The "hard drive" is getting full .

 

If I'd bothered to look up the actual typical analysis.... I'd have posted that.

 

best,

 

..............john

[Guest JBaymore]

Everything that outgasses from the clay and glaze mateials is in the kiln effluent circulating in the kiln. Also anything that is contained in the fuel source. Cooking using direct hot gasses from the kiln is subject to this situation. Generally... it is NOT a great idea. There are other ways to accomplish this task that are safer.

 

So a lot depends on what the clay and glazes contain and how hot the firing is (relaive to the potential outgassing / volitalization). For example, copper copmpounds are notoriously hard to keep in glazes in most temperature ranges. So there likely is some copper fume circulation in any kiln that has copper in the glazes. The more pieces with copper on them and the higher the percentage of copper in the glazes... the more there will be in the kiln gasses.

 

Of course lead compounds are the really scary ones that "everybody" knows about.... however many other ceramic compounds volatilize.

 

And glazes are possibly still outgassing on the cooling cycle for some time... so ..... no guarantees there either. Once the kiln is no longer glowing.... any of that likely has stiopped.... but you do not know what fumes (tinly little particulates) still reamin in the kiln at that point.

 

As far as a wood fueled kiln goes....... if you wood supply is "clean" then it is no different from THE FUEL than going to say a wood fired pizza place. However if you happen to be burning scrap wood with paint or finishes, pressure treated (god forbid!), plywood, particle board, MDF, and so on..... there is TONS of bad crap in the kiln gases coming from that stuff alone.

 

If you want to cook on a wood kiln, you can build a dampered ducting system off the firebox that allows you to direct really hot gases to the OUTSIDE of a refractory structure that then trasnsfers the heat energy by conduction to the inside of a small "oven". The heat coming by conductive/radiant means to the food... not convective from the kiln gases. MUCH safer.

 

 

Years ago I did a kiln installation project for a client where we used heat exchangers running propelyne glycol collecting fluid through the exterior kiln shell (not in the chimney) to collect waste heat leaking through and stored in the refractoy structure to heat a huge solar-type hot water tank located in his studio to supply heat for the space. The liquid method removes the issue of the really important INTEGRITY for kiln effluent to clean air air-to-air heat exchangers for domestic heating.

 

best,

 

................john

[LilyT]

Lil,

I would just stay away from cooking and kiln exhaust. Many years ago there were designs for channeling kiln heat in heat exchangers, but there was not cooking. Maybe if one used radiant heat sealed from exhaust fumes, it might not be a hazard.

I have used spodumene as a feldspadic flux as John mentions, but I have never used it as a wash. Maybe it would give a similar results as colemanite (Gerstley Borate is the contemporary substitute for Colemante) washes as used by Voulkos. I can't say, since I have never tried it.

Marcia

 

 

Marcia, it's definitely a question what each kiln's exhaust might contain. Maybe I'll

just steal some extra hot bricks from kiln when it's cooling down and use that

as a hot and radiative cooking surface. Bread ovens cook using the re-radiated

heat from the mass of the oven, rather than direct fire.

Thanks for your comments!

-Lily

[LilyT]

Spray Gerstely Borate on instead.

On the subject of cooking with wood-kilns;

Build a box of hard brick about 3 ft long by 2 ft wide. Shovel in some coals and embers from the fire box. Bury your casserole. You can also put a piece of boiler plate[ thick metal sheet 1/2 inch thick] on top of your box. On this you cook hamburgers and hot dogs. The fire box of your kiln would be WAY too hot to cook anything.

TJR.

 

 

TJR,

That is a very generous cooking box indeed! I think you can

feed a restaurant with that - I approve (Or did was that the ouside

dimension?). Boiler plate is an interesting idea :-) too.

And I'd have to differ on the opinion that the kiln box is too

hot to cook anything. We've made instant roasted marshmallows

in our firebox (clean wood, from saw mill processing local

trees). One microsecond and perfect :-). Otw POOF! Lol.

Thank you for your comments!

-Lily

[LilyT]

Everything that outgasses from the clay and glaze mateials is in the kiln effluent circulating in the kiln. Also anything that is contained in the fuel source. Cooking using direct hot gasses from the kiln is subject to this situation. Generally... it is NOT a great idea. There are other ways to accomplish this task that are safer.

 

So a lot depends on what the clay and glazes contain and how hot the firing is (relaive to the potential outgassing / volitalization). For example, copper copmpounds are notoriously hard to keep in glazes in most temperature ranges. So there likely is some copper fume circulation in any kiln that has copper in the glazes. The more pieces with copper on them and the higher the percentage of copper in the glazes... the more there will be in the kiln gasses.

 

Of course lead compounds are the really scary ones that "everybody" knows about.... however many other ceramic compounds volatilize.

 

And glazes are possibly still outgassing on the cooling cycle for some time... so ..... no guarantees there either. Once the kiln is no longer glowing.... any of that likely has stiopped.... but you do not know what fumes (tinly little particulates) still reamin in the kiln at that point.

 

As far as a wood fueled kiln goes....... if you wood supply is "clean" then it is no different from THE FUEL than going to say a wood fired pizza place. However if you happen to be burning scrap wood with paint or finishes, pressure treated (god forbid!), plywood, particle board, MDF, and so on..... there is TONS of bad crap in the kiln gases coming from that stuff alone.

 

If you want to cook on a wood kiln, you can build a dampered ducting system off the firebox that allows you to direct really hot gases to the OUTSIDE of a refractory structure that then trasnsfers the heat energy by conduction to the inside of a small "oven". The heat coming by conductive/radiant means to the food... not convective from the kiln gases. MUCH safer.

 

 

Years ago I did a kiln installation project for a client where we used heat exchangers running propelyne glycol collecting fluid through the exterior kiln shell (not in the chimney) to collect waste heat leaking through and stored in the refractoy structure to heat a huge solar-type hot water tank located in his studio to supply heat for the space. The liquid method removes the issue of the really important INTEGRITY for kiln effluent to clean air air-to-air heat exchangers for domestic heating.

 

best,

 

................john

 

 

Hi, John,

Yes, good point about the fuel source contributing to the kiln effluent. I only

fire with clean wood sources because the family grabs wood from the same

heap to barbecue with!

That is so interesting about the copper volatilizing at any temperature! I am

aware that metal fuming say in raku firing can be a big issue. (I know that

my lungs hurt after a few breaths near some kilns even though they are

in an open area.) So much glaze in food safe ware has copper in it, do you

think there's a safe temperature range below which the glass locks in the

metal (finally) - that's probably on the inside of the firing/cooling kiln though,

and likely potential outside cooking surface would be much cooler (well, perhaps not since

I was considering using cordierite as the roofing on that part of the kiln)

And also, I agree and you've stated it so much clearer than I did, that

I'd be interested in scavenging the radiated/conducted heat, rather than the

direct hot effluent. I hadn't thought of using anything directly from the firebox,

I'd be too stingy with any high temp heat to share it :-). My thoughts mostly

ran to the re-radiated heat. With a long wood firing, conduction out through

any brick or refractory that is not 'insulating' is pretty fierce while the kiln

is on the cooling/fire-down. So sharing a wall with the kiln was my original

design. But perhaps I'll just warm up a pizza box on the top of the cooling kiln, lol.

 

That sealed propylene glycol heat exchanger sounds really neat, but

would be too high tech and high maintenance for me :-(. My personal

approach to kilns is unfortunately limited to techniques that can stay

safe with lots of tolerance for change, movement, and entropy. Big

safety margins for error need to be in place because I don't fire by

myself and the unexpected can take place in the blink of an eye.

 

Thanks so much for your detailed information and clear thinking! I love

knowing the nitty gritty.

 

-Lily