So I've been experimenting for the past couple months with blending various local materials into a C6 stoneware clay that I've used successfully for many years in pit and bonfire firings to give it a bit more character for raku firings. I've settled on two blends for the time being, one lighter and smoother in texture, and the other darker and more gritty. They both take the thermal shock of firing well and give me the color and character (or taste) that I'm looking for, but they both share one small problem. I think I've figured out a work-around to fix it but I thought I'd run it by the more knowledgeable folks here to see if there's any variables I'm not taking into consideration, since I am a relative newbie to this clay chemistry stuff.
The problem I'm having is small particles (1-2mm) of limestone from the local silts and grits that I use popping out of the clay/glaze surface after firing. Shouldn't be a huge problem right? Just use a finer mesh sieve to remove larger limestone particles, right? Well, unfortunately I can't do that because I've (stubbornly) decided the texture of the clay is perfect with the larger particles of grit I use for temper and I don't want to run it through anything finer than a 1/16" screen. (photos below)
I have to mention as an aside finding limestone grit in my native iron bearing soils was not a surprise - heck, everyone around here who uses well water knows how hard with iron and carbonates it is. I just didn't know to what extent it would show up in the clay until I fired it.
So, since I decided I can't sieve it through a smaller mesh, I've thought about dissolving the particles with vinegar. We've always used vinegar to get rid of calcium carbonate build up on our glasses and our house humidifier, so I thought using some apple cider vinegar in lieu of water when I'm sieving the limestone bearing soils before I mix them into the base clay could alleviate the problem. Plus, if I remember right, I read somewhere that some old time potters mixed in vinegar to help with plasticity. Unless there's something I'm completely missing this sounds like a win/win right?
Please forgive the photo quality (glaring highlights), don't have a lightbox setup yet to photograph my stuff.