Friday, September 9, 2011

Clay Dig Update

A few weeks back I posted three videos (see them below) showing how I process and test hand dug local clay. Here is an update of the results.
Here is a pint sized mug that was thrown from clay that I dug from a trench just a mile from my house. This was straight dug clay without any additives. It threw well (see video) and fired pretty well too. I fired it to cone 04 (earthenware temps) first.  At that temp. it was underfired and quite porous. I believe that was because of the abundant fine silica  sand in the clay. I fired it again to cone 6 with good results. It fired to a dark red-brown with 3% absorption and 10% shrinkage. It is glazed with  a slip and ash glaze that consists of 50% local slip clay and 50% wood ash from the woodstove. The inside has a pebbly, almost salt glazed look. I think this is because the soils around the Red River are high in salts and are quite alkaline. I think the salts in the clay interacted with the ash glaze.


 I have been using the mug in the shop daily for the past two months. It has been through the dishwasher many times with no ill effect and has been used for everything from rootbeer to cider. This clay should work well with a bit of flux (PV clay), a little ball clay and some grog.


 

The test bar was 5" long when we started and is now 4 1/2" . That is a 10% shrinkage. It was fired with  each end resting on a piece of broken kiln shelf. It did not sag at all. After firing it was weighed then soaked in water overnight then weighed again. It had absorbed 3% water. This is acceptable to me as a mid-fired pot. With a a bit of flux this absorption will be even less.


Clay Processing Videos
#1



#2



#3

8 comments:

Gary said...

Great info and videos. If people would just experiment a little with the materials around them locally, they would be amazed. I use mostly locally-dug clay and prefer it to store-bought. Occasionally, I pick out a root or pebble, all things that potters have done for eons. I would say almost every locality has native clays that can be used with a little adjustment. It is VERY satisfying!

Wildmud said...

Thanks Gary. I'm working on a series of sculptural pottery using local clays and materials. I want to use them as dug when possible and let the properties of them dictate what i am able to make. It will be a couple of months before the first series is ready to show. I'll post more then. Good luck and happy digging.

Anonymous said...

Nice vids. Interesting to the layman who would like to dabble in different projects with the kids. Thanks for sharing.

Matt H said...
This comment has been removed by the author.
Matt H said...

does clay have to dry on a plaster surface

mokapottery said...

Thanks for this great step by step. Can't wait to have a go; we have tons of local clay in this part of Stirlingshire.

Kath

Anonymous said...

Hi!!I'm new to throwing and absolutely am IN love!! Love the idea of using local handmade clay..loved the videos as well.!!We sit on TX/OK border round 20miles from Red River and was told that the clay here wouldn't work because it is red clay..and doesn't have the right mineral chemistry for throwing and firing. What would I have to add to make it right for throwing and firing? or is it more of a trial and error type thing? ThanKssomuch!!

Randy Crawford said...

Congratulations on your successful clay mining demonstration!
The glaze fired mug from your test looks very good. The glaze fire was cone 6?
I guess you have used that formula before on native clay from your area,
because i am assuming that the glaze fits the clay well. have you tried a clear or
translucent glaze on the same clay body?