Friday, March 28, 2008

Up Next: Soda Firing!

I spent Wednesday waxing, glazing, and mixing wadding and soda salad (moron that later!) for the soda firing. Wadding is used to prevent ware from sticking to kiln furniture, and is used in salt, soda, and wood fired kilns. I use a pretty standard recipe:

4 lbs kaolin
4 lbs alumina hydrate
2 lbs medium grog

I wax the bottoms of the pots, because the wadding sticks to wax better than to bisqued clay. This works best when I am loading each piece immediately after wadding. When circumstances have required wadding ahead of time, such as for an enormous kiln load, or for a large-group firing, it's better not to wax, and instead to use a little dab of Elmer's glue to keep the wads in place.
It should be noted here that I haven't fired a salt kiln since graduate school -- I ain't saying how many years ago that was -- and I haven't done a soda firing, except as a workshop participant, ever. So I had a lot to be nervous about, and there were a lot of mistakes waiting to be made. Let me tell you about one, and I hope it is the worst one:
I had some doubts about how to introduce the soda. I've seen it sprayed into the kiln, but that seems like a lot of rigamarole and equipment; I'd heard of people making "burritos" out of soda ash and wet newspaper, and that seemed like a good way to end up with a lot of dry spots in the kiln. (Dry spots being places where the vapor didn't reach, which thus got little or no glaze. What I wished for was a way to introduce soda the way I used to do salt: Place it along the length of an angle iron, stick the iron into the port, and dump the material into the flame. I found it, finally, on Emily Murphy's page. Emily recommends mixing soda ash, bicarbonate of soda, and calcium carbonate with wood chips and water to make a paste the consistency of tuna salad, and the spreading that on an angle iron to insert into the kiln. What she didn't say, but I should have known, was not to add the water until shortly before using the mixture. I mixed it all up on Wednesday, and by Friday it was a concretized mass. The soda undergoes a chemical reaction with the water turning it into hard crystals that I had to break up with a big scale weight I found lying around. That stuff stings the skin, too!

Another unexpected element was a late season snowstorm. Actually, firing in the snow is not that bad. What really stinks in loading in the snow. Unloading is Sunday -- or Saturday night if I just can't wait.


Douglas Watts said...

You didn't mention my third degree burn.

Waa ...

Lori Watts said...

I thought it was too personal, given where it is located.

Emily Murphy said...

I will update my site to mention not to mix the soda up until the last minute. The other important piece of information is that the water you add should be COLD water. Hot water will speed up the hardening of the mixture and make it difficult to work with. Another reason why mixing it up at the last minute is important is that the water in the mixture is important to getting the soda to vaporize and really move around the kiln.