Monday, June 28, 2010

Going Native

As a Native American artist attending Native American shows and selling Native American pottery one must pursue the ancient methods if one wants to enter the competitions. At most Native American shows there are competitions where you have the potential opportunity to win significant sums of money, at least as much as part of your booth fee. It is also a good opportunity to become better known in the Indian art community. These shows are all juried and quite competitive. I am a rather late comer to the Native American art market. Many of the artists I compete against have been doing their art since they were practically babies.

So far I have only made it into the pottery categories at these markets. I have been doing one sort of ceramics or another for more than 20 years but I've always bought my clay at the ceramic shop and fired things in an electric kiln in the past. For Native American show competitions this severely limits my prospects for prizes as most pottery categories in the pottery competition require that the items be made from Native materials and Traditionally fired. This means you have to dig and refine your own clay and fire it outside in a wood fire. Furthermore many of the traditional pots are black.

Scientifically getting black pottery from red clay is a simple result of having the pottery in an oxygen starved atmosphere, known in the pottery industry as reduction, at a specific temperature when the iron oxide that makes the clay red is somewhat unstable. At this point it will give up oxygen to the starved fire and in doing so changed from iron oxide to iron magnetite (Fe3O4 which has only 1.33 oxygen atoms for each iron atom) If it is fired and cooled in an oxygen rich atmosphere the iron oxide in the clay becomes red hematite (Fe2O3 with 1.5 oxygen atoms for each iron atom). The black clay can be made red again by once again raising the temperature to that point in an oxygen rich atmosphere.  You may have seen some native pots that are mostly black but have streaks of red here and there.  They accomplish that with a torch on the surface of the pot, thus bringing that area of the pot to temperature in an oxygen rich atmosphere.

Now this all sounds very simple and straightforward sort of like the way those glasses will get dark in the sun and clear again in the shade. But in a wood fire it is a bit more complex as I have discovered. Some of the information I have is empirical and not as scientifically defined as the basic process above. If you have a fire that is somewhat starved for oxygen but is still burning you tend to achieve partial reduction which turns the clay a sort of gray-tan color like the pot in the photo to the right.  How it ends up tan I'm not sure perhaps is it an optical illusion.  You can see streaks and areas that are more gray.  I would have expected to see it more of a red with gray areas but that is not what we ended up with here.  But I am not a chemist so I don't know what the iron did in this pot except that it didn't turn all the way black and it didn't really stay red.  So I know empirically that the fired had too much oxygen through that critical temperature range to turn black but not enough to be red.  Now these colors are 'in' the clay not on the surface.  This is not a residue that sits on the surface of the clay.

Ok so this should be pretty simple starve the fire and it will go tan starve it to the point of extinguishing it and it will go black.  But sealing up a fire even one in an enclosed area such as a barrel, kiln, or pit is harder than it sounds because there is oxygen everywhere and you have to seal it up pretty good.  The tan pot was from the first firing that I made in my artificial 'pit' enclosure.  Due to fire regulations I can't just dig a pit in the ground and start fires in the open during wildfire season so I have to have the fire enclosed.  Some people do this in 55 gal steel drums I built a brick enclosure.  Logic says when you get the fire as hot as you want add extra fuel and then seal up the enclosure.  The additional combustable should burn up all the available oxygen and you should have black pottery.  Well that might be true if you could just hermetically seal up the enclosure but as I found this is not very likely.  We plugged the opening where we were feeding the fuel in and plugged the opening that was acting as a chimney.  It did start smoking but the fire pushed its way out around the plugs.  We put dirt over it and kept putting dirt here and there over every little place that we could see smoke and fire emerging.  Thought we did a pretty good job of sealing it up but in the morning I still had live coals which means that somewhere there was air still getting in.

For the second firing we sealed up the enclosure a bit better and tightened up the plugging methods.  Also we added a common combustible/smothering agent that is used by many Native American potters to smother their fires, cow dung.  We added this through the chimney hole right on top of  the pottery.  At the same time we plugged the fire hole and then plugged the top as well.  Well we produced more smoke than you can imagine and still had smoke pouring out in numerous places.  Places you can't imagine even like out from under neath the enclosure which is sitting on concrete bricks.  More dirt over everything and as you can see most everything ended up pretty black.  But there are a few anomalies for example the tiny pot shown on the left.   As you can see his head is tan while his body is black.  How in the heck did that happen?   I'm not totally sure but the only thing I can guess is that the cow which was covering him continued to burn with enough oxygen through the cooling period and he somehow just didn't go all black.  Some of the pots that were on the edges of the enclosure such as the bowl and ones that were totally covered with the cow also have small areas that aren't totally black.  And again I still had coals in the morning so air is getting in somewhere.

So the quest goes on.  You can see photos of all the pieces in these two firings in my Facebook photo album Wild Clay Fired   Previous Native pieces are on my Native American Art page at Natika's Native American Art   Most can bee seen in the gallery or in the pottery shop.

2 comments:

  1. Fascinating, Marsha! This is a very thorough explanation of this process, thank you!

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