Reduction firing?

Hi Marianne,

Reduction firing in an electric kiln is possible, but not recommended, as it damages the elements and will produce lots of nasty gases and/or smoke. You really need to reduce in a gas fired kiln.

Dave

My electric kiln is quite small, so it might be in my future to buy/build a bigger kiln. Is it possible to combine oxygen and reduction firing capabilities in one kiln? I have an outside space that might be usable for a larger kiln in time.

Marianne

All glaze materials should be considered toxic, esp when dry, though yeah lead etc are worse. A way you can try it a little is in a saggar. Make a large lidded pot out of toothy clay fill it with sawdust and pots with reduction glazes. I have not personally tried it, but apparently it can work.

In article , Bubbles writes

Hi Marianne,

Fuel burning Kilns are very flexible, so you can do almost any sort of firing in them, though if you do salt in one you can't really do anything else in it afterwards.

Steve

Raku is a good way to do a kind of reduction firing without building a new kiln just get a pully rig for your electric and a large metal can full of sawdust with a lid,put some copper into a clear or white glaze and you can have fun with the effects of ruducing the oxygen in the attmosphere of your glaze firing. The reduction is done in the sawdust ( it needs the oxygen in the glaze to burn) within the closed lid metal can. The copper will give you some red and you don't need to fire any where near cone ten. Lots of room for experimenting. I've even done this kind of reduction one pot at a time in a small test kiln without cones just eyeballing the glaze through the peep hole and removing the pot with a small pair of tongs and those special leather gloves for raku. Great instant low fire reduction fun.

I do miss those cone ten reduction firings of my early pottery days sometimes tho

Nancy Jane

v

The glazes I use are "giftklassefrei", ie. no poison class, and are liquid paint-on ones. With the tiny space I have, the dust from the dry clay is plenty enough, so I try to avoid other dry materials. Though I could always go outside and mix a reduction glaze and put it in a pot for painting :D

I've done a bit of googling about saggar, and the saggar-fired stuff I have found looks similar to raku, with burned patches, though these are more brown than black.

I don't see how I would achieve reduction for the whole piece using that technique. Also, it seems the burning of "stuff" inside may produce poisons, so the pieces wouldn't be food-safe?

Marianne

Just a thought "special leather gloves for RAKU", not really a good pair of welders' gauntlets will do the job (usually for longer) and are about

1/2 the price (in my humble experience) difference betwixt ART stores and industrial... Same goes for goggles, i use welders goggles (about £4 the pair with replaceable lenses)and the SAME goggles are on sale thru a Artists catalogue at £25 the pair..... We all get to make a living, It's who gets to make a living off us That is the issue... Hugs Eddie

I haven't actually done this either. However, the "stuff" would typically be sawdust or something like it. It is unlikely there would be any toxic metals in it, as long as you don't use sawdust from "treated" lumber (which contains copper and arsenic).

As far as producing toxins from the combustion itself, there could be various carbon compounds, like you might find on overcooked food, burnt toast, etc. Some of those on food can be carcinogens. However, the carcinogens have complex structures (benzene rings, etc) that are totally destroyed at kiln firing temperatures... all you would have left is pure carbon (plus whatever residual silica and such was in the wood ash). No "polycyclic aromatic hydrocarbons" or anything like that.

Further, even if there were some of these nasties (as there might be in the quicker raku-type reduction), they would only be a problem if the ware surface was porous (like raku), which you wouldn't want to use for food in the first place. On a glazed surface, they would just wash off, though maybe with a bit of scrubbing.

So if you are at all inclined to try saggar firing... go for it! (And be sure to tell us of you experience!)

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Home of DaqGen, the FREEWARE signal generator

Home Depot gives away bags of Sawdust (just bring in heavy duty plastic bags) and they will not cut wood that has chemical preservatives in it so what you get is chemical free (well wood is a chemical but we all now what I'm talking about). I'm sure Lowes or other such places will happily give it away as well.

I'm a bit curious on how in the world you would do this inside an apartment or house. It is one thing to open up your electric kiln while hot but then to put your pot in a can with burnables and not smoke up your home.... I have never heard of anyone doing this until now. Maybe I misunderstood and the person who suggested it in the first place had their kiln outdoors. Did I miss something?

But that is not a glaze is it, just acrylic paint? Not food safe I would think. See

the tiny space I have, the dust from the dry clay is> plenty enough, so I try to avoid other dry materials. Though I could > always> go outside and mix a reduction glaze and put it in a pot for painting :D >>> A way you can try it a little is in a saggar. Make a large lidded pot >> out>> of toothy clay fill it with sawdust and pots with reduction glazes. I >> have>> not personally tried it, but apparently it can work.>

Thanks, great tip!

Actually, I had forgotten that she was talking about inside an apartment. ;-)

However, I have heard of people sealing their saggars with something before firing, but I'm not sure what it was. You might even get away with using wet clay, if the mating surfaces were previously coated with kiln wash or something so it didn't fuse the saggar lid and body together. Anyone know about this?

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Home of DaqGen, the FREEWARE signal generator

People often have portable raku kilns - gas bottle and do it outside, then the smoke etc when you thrust the piece into combustible material doesn't matter.

This started out as Marianne wanting to know about doing reduction firing. She only has is an electric kiln and not much room. I made the silly assumption that she was limited to the indoor electric kiln (assume makes an ass out of u and me.). So how much clearance outdoors do you think you would need for a small raku kiln (how big a back yard)? Many years ago we made our own but it wasn't really portable - may have been the heavy, welded iron frame... You could certainly get away with a very small kiln for raku. Could it be fired on a patio without burning down the apartment building??? I suppose you could insulate the trash can that you reduce the pot in...

We had a raku kiln that was simply a trash can (nz'ers say rubbish tin :) The bottom was cut out, a bit of ceramic fibre wired onto the inside of it, then on a a few fired bricks you stack your work on small kiln shelves - we had broken pieces, the gas bottle feeds from underneith, the whole trash can lid and all is just lifted on and off by two people wearing gloves and with long tongs. Then when you think it is hot enough lift the lid off and then plunge the pieces into saw dust - we had it in a large enamel pot and put the lid on. We worked in the car park. I would be pretty wary of working on a deck, and definately not inside. There is quite a lot of info on raku firing on the net and how to make much better kilns than our trash can one.

One Huge Snip .......................................................

Raku is an outside activity.

As far as reduction is concerned. Moth balls thrown into a kiln is a possible approach. One has to be careful if they are trying this form of reduction in electric kilns because the reduction process may reduce/attact the heating element. Silicon Carbide in glazes work also but needs to be tested out on the particular glaze in mind. Can cause pinhole or craters which may have cool and interesting effect. Firing temperature plays an important role in this process too.

Hope this helps

Reduction misfiring in an electric kiln is bad for the elements for the following reason: Every time an Electric kiln is fired with a normal internal atmosphere, a microscopically thin lair of oxide is formed on the surface of the element. Ultimately this layer of oxide does two things, it protects the element itself from an attack by moisture which combined with heat is highly corrosive, but it also reduces the working core of the element by the same amount. When you produce a reduction atmosphere in the kiln, that thin layer of oxide is stripped away, leaving the element unprotected, and effectively shortening its life. The oxide layer can be replaced by firing the kiln up to about 800 degrees centigrade without anything in it! However some damage will have been done during the previous firing.

As an addendum to this, most electric kiln manufacturers recommend a low temperature firing with the kiln empty after replacing any or all of the elements. To do so definitely increases element life.

Steve Bath UK

In article , tigre writes

Ahh well what I got was in German but it also had in big letters 1250C so yeah glaze :o) When you posted before I googled the name and it came up with paints ceramics....