I really dig clay...literally

No one on my volunteer list showed up, but luckily Alejandro Zuniga and Connor McGaughran came to my aid for the August 18 clay dig. More accurately, it was clay prospecting. The idea was to get samples that my advanced students will be testing this fall. 
More than 5 years ago Walter Heath and his students processed quite a lot of clay that was dug on high ground, on the Eastern edge of the East 40. We have been working with that wonderful stash of clay ever since. But that clay isn’t going to last forever, and before we do any large or even medium scale processing of clay, I want to know what we’re going to get. For comparison, I went to one of the lowest lying areas.

The new site; Alex had put a tarp on a week before the dig to kill weaken the tangle of weeds that were in this new dig location.

We took three 5 gallon buckets of clay, the first 18 inches down, the next about 30 inches down and the last bucket at 44 inches in depth. The color became more purely orange/gold the deeper we went. 
In addition to testing the clay locations, I want to compare dry vs. wet processing. So I’m not only going to test the new location with the existing clay which was wet processed, but the new location with clay from the old location that will be dry processed. Luckily for me, there is a significant amount of quite pure clay that has been sitting in a pile in be old location!   

We pulled the tarp to the side, and pot the topsoil on the tarp, topmost layer to the right and deeper layers going to the left on the tarp. That way, after digging, we could replace the soil in its correct layering.

There are advantages and disadvantages to either dry or wet processing of clay. I fear that the wet processing that was originally done may be superior, but before I go there I want to test for myself. Is a significant difference, which is easier, and which is gives the better quality of clay? Both wet and dry processing use screens of decreasing size first to screen out larger things likerocks and roots etc., then to get increasingly fine particles of clay with screens that have smaller and smaller openings for the material to pass through. In the wet processing, gravity is used as well; the heavier materials fall to the bottom of the barrel while the lighter ingredients are pumped of the top into the next bucket and the process repeated until you get the level of fineness that you want. 

The original wild clay from the East 40 we have been using, until mixed with other ingredients into a clay body, is very brittle. It lacks plasticity, that is the soft pliability that we want in clay. It cracks very easily, and it’s hard to cut it without tearing the clay. On the plus side, it has low shrinkage and beautiful color. It’s obviously iron-rich, but I don’t know the precise chemical composition. Maybe I can find someone in the chemistry department willing to test it. I think it’s unusually high in alumina, because on pots made with the clay even glazes known to be very runny stop being runny. It is actually a spectacular glaze ingredient, a kind of mysterious “special sauce.” 

I was really happy we were able to get samples from a new location at 3 depths to test. Even just processing and testing small amounts is a lot of work. Keep checking in to this blog to see how that evolves!