My husband recently dug clay from a clay hole that his tribe has used for years, and the clay vein was so smooth that the clay peeled off the walls of the clay hole. He and other tribal members thought they'd found the best clay yet from that spot. It's now been dried, screened, soaked and dried to workable consistency. It wedged up beautifully but they find that the clay has no strength! A coil-built pot sags under its own early weight.
His thought is to return to the clay hole and dig what he would consider poor clay, process it, and add it in. But I wonder if anyone has a suggestion about an additive that would add significant strength without drastically changing the color of the clay, which is a deep brownish- grey color, which fires to a tan or yellow-brown. This clay is slightly darker and more grey than the clay that is usually acquired from the hole, making us wonder what is missing. The pots will be burnished, preheated to 500 degrees and fired on the ground in the traditional way. Any help is greatly appreciated, since the clay hole is inaccessible during hunting season, which has begun. I've attached an image of a fired pot.