Wow! Two posts in three days. Things must be happening (apart from the background hours of calcining, crushing and grinding).
I've been fortunate enough to be invited by the archeologists at Cambridge University to one of their dig sites in North Cambridgeshire, to investigate the various clays on site and (hopefully) give some insight into what was used to produce the various types of pottery found there. A slightly surreal place on the edge of the fens, where layers of deposition are removed one at a time to expose the ground level of a particular point in history. This drainage ditch was dug in the late bronze age.
I was able to see examples of the pots produced there, some of which were quite finely made and rather beautiful.
What was of most interest to me and this project was this section that had been cut through the ground exposing hundreds of years of deposition around the courses of ancient rivers. Many of these deposits are river clays, including the Fenland Buttery Clay, which I have been trying to get a sample of for ages.
The red/brown seam at the bottom is iron oxide, that has been dissociated from the upper layers, bleeding out from a very thin seam at the base. I have read about this occurrence and how it 'lightens' the clay deposits over time, but never seen such a fantastic example.
Back home now with many many clay tests to do. i am also going to fire some old pots shards to different temperatures to try to ascertain which clays they were made from.