I know it probably seems like I haven’t been working because I haven’t been posting. I have been working—it’s just the boring behind-the-scenes stuff.
Since the disaster in April, where my clay got contaminated, I’ve dug and processed probably 600+ lbs of clay. Processing involves drying the clay completely (so that it will break down in water), and settling out the sand and/or sieving to remove lumps and rocks. Then the slurry has to be dewatered to a workable consistency.
My clays are sandy and vary a lot depending on where I dig them and how deep they are. Each batch has to be tested. I had one batch that I did a line blend with, and got one test tile that was perfect. So, I mixed up the rest of it with the needed feldspar and made (and bisque fired) a bunch of stuff—then realized I hadn’t tested the full batch (absorption turned out to still be 4.5%). That was a huge time sink. I’m not sure where I made the mistake.
I was excited to find some stuff that fired to low absorption at cone 6, but despite my best efforts (testing with Darvan), I couldn’t overcome the high drying shrinkage. I decided to mix it half-and-half with a batch I had tried to use (unsuccessfully—too much iron for reduction firing) at cone 10 that had quite a bit more sand left in. The cone 10 stuff had been sitting for a while and was dry. Instead of breaking the cone 10 stuff down separately in a bucket and making sure it was smooth before adding it to the other clay, I thought it would break down fine and added it directly to the slurry. Well, it didn’t break down after 3 days of alternating sitting and mixing in the cement mixer. I ended up having to sieve it all to get the lumps out. I dewatered a sample, fired it, absorption tested it, and added 15% feldspar to the entire batch, thinking that would be perfect. I repeated the sample testing—the dewater, fire, and absorption test (keep in mind this testing step takes several days, as it takes at least a day to dewater, at least a day to dry the test bar, a day to fire, and then a day to test the absorption). Absorption was still too high. So, I added 5% neph sy (a better cone 6 flux) to yet another sample. Its absorption is 2.7%, and I just got that sample finished testing this morning. It’s really close but not quite. So, I’m going to up the neph sy and add it to a larger batch, keeping everything in the cement mixer until I get a good test.
Hopefully, I will have about 75 lbs of clay to actually make things with. In order to mix stuff that’s in slurry form, I have to dry a small sample, calculate the water content, and then mix the larger batch. It’s faster than drying the entire batch and then adding the water back (and risking lumps—see above) but all the drying and dewatering takes time.
I also had another tub of stuff that had been sitting and was dry. I reprocessed it to get more of the sand out, and I’ve got a sample of it set out to dewater so that I can make a test bar.
The huge black tub of clay…I tested a sample of it, and the absorption was 16%. I added 20% neph sy to yet another sample, and the absorption is still 11%. I think I’m going to try 30% neph sy and see if that works, but I’m worried the clay won’t be plastic enough with that much. If that proves to be the case, I will have to reprocess it to remove more of the sand. I will hopefully be mixing this test today.
Fun times all around.
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