WARNING! Even more technical content than yesterday. But it's my blog and my little record and I know some of you are fascinated with science. OK maybe not, but you tolerate my dalliance.
These are the bronze clay pieces I fired yesterday, all cleaned of carbon, and shined up with a wire brush. What I didn't mention was that these were fired in coal based activated charcoal. In the literature (which is actually scanty) the patina you get with this firing medium is unpredictable, partly because of the mineral impurities in the medium. I actually suspect it is a combination of both the reduction firing and the impurities. This reminds me a lot of the flashing you can get on raku with copper glazes/washes when you apply post fire reduction. Given that bronze alloy has a large component (majority) of copper this makes sense. At least to me.
I'm liking the surface of these pieces now. They have a sense of antiquity, of old coins. And unlike raku they have a permanence. How long? Don't know. These are definitely a time will tell thing. There really is that little experience with the long term stability of surfaces in this kind of work. I do know that really vigorous, really rough wire brushing does not remove the patina and does not scratch the surface. This stuff is tough!
One of the pieces I made was a tiny little disk, purely for potential experimentation with etching. I cleaned the piece up, used a marker to apply a resist. Then suspended it in 'Etchant' for 30 minutes. (I have 1 of 8 bottles still on the shelves of Radio Shack as of 3 weeks ago here in my small community). Nice job of stripping away the patina! And the resist. Nothing.
I really, really wanted to see what it might look like to contrast that dark patina with fresh raw bronze. So I flipped it over and used acrylic paint. Thickly applied acrylic paint left to cure. Well I got etching, but it seems that it eats under the patina surface. The surface just peels off. Oh well. More experiments, maybe? Any ideas out there?
Just one last little note. Even though I fired these pieces as best I could with the standard firing schedule. I think they are just a wee bit over fired. There is just the tiniest bit of pitting in the surface and a wee bit loss of detail. They are fully sintered (fused together) but a little overdone I think. Kind of like cookies that get a bit tough because you've over baked them by 2 minutes.
Off to the porcelain tomorrow. But more development of this in the works!