potziller Posted November 10, 2013 Report Share Posted November 10, 2013 Hi Guys, while digging some clay (of the usually brown type) I unearthed a small deposit of grey clay. Within the grey clay there was very small amount of distinctively green/grey clay with a green/grey stone in it. Any folk got a clue or two to why this 'clay' was different? I've kept separate from the other clay I dug that day and did the usual drying out and slaking down with this curious stuff. It slaked down with no fuss, but once I'd blitzed it with hand-held food processor and screened the 'gritty bits', it 'almost' refused to settle out. What settling there was was minimal and very slow to show. Eventually I poured it onto a plaster bat and got a ball of clay (yay!). No idea if it's 'good to go' (I'm a nube when it come to dug clay) and there isn't enough to 'test' shrinkage etc; so has anyone got any ideas to what I got 'balled up?'. I could mix it with some 'other' clay, but at the moment, I'm curious to this green/clay's make up and qualities. Any best guesses welcome! Ta mutchly, V:) Link to comment Share on other sites More sharing options...
TJR Posted November 10, 2013 Report Share Posted November 10, 2013 O.K; I'll bite. I think you have some organic material in there. I have a very dark clay, that when fired comes out pink in the bisque and brown at stoneware temps. Here's what you do; 1 Place said green clay[after completely drying it], into a bisqued bowl of a clay that you know will take that temperature. 2.Fire it up to bisque temps and see if the green colour remains. 3. If it does, you have a mineral like copper in the body. 4.If the colour burns out, then you had some kind of organic material like mould,fungus, a new life form. 5.If it melted into a liquid, you have a material for a slip glaze ala Albany slip. 6. Enjoy your new found wealth. TJR. Link to comment Share on other sites More sharing options...
smastca Posted November 10, 2013 Report Share Posted November 10, 2013 We have the same thing with our Queenston Shale Clay deposits. I've an old government document that talks about all the different types of clay in Ontario and even gives the chemical breakdown of each type. This is a paragraph from the document: Thin green bands parallel to the bedding, and more rarely at right angles to it, have been formed by the reducing action of acidic groundwaters. Green Shale constitutes 5-25 percent of most Queenston sections. Queenston Shale is readily broken down by weathering, forming ultimately a red clay soil with superior ceramic properties. Composition The Queenston Shale is remarkably uni form in chemical and mineral composition from top to bottom of the formation; minor varia tions have been pointed out in a previous report (Guillet 1967, p.59). Lime content is most variable, ranging 3-18 percent in brick quarries of the Toronto-Hamilton area, re flecting the proportion of green shale beds in the sampled section. Green shale is harder, more limy and less easily broken down by weathering. Colour and porosity of the fired ware is there fore dependent to a large extent on the propor tion of green shale in the section. You can also see this in the Caledon Badlands: Take a peek at the image. http://www.trekearth.com/gallery/North_America/Canada/Central/Ontario/Ingelwood/photo888000.htm Is it similar to this? Link to comment Share on other sites More sharing options...
potziller Posted November 10, 2013 Author Report Share Posted November 10, 2013 My head hurts! And digging the clay was so much fun! Thanks for the replies folks. The balls of clay feels a bit like plasticine and seems to keep itself to itself - doesn't transfer to the hands now it's a ball, like porcelain does - also looks glossy. You know, a question that was upper most when I truly started out with clay was 'what's the difference between earthenware and stoneware?' The answer back then was one fires at a higher temp and both have their names on the bags. Now the question is uppermost again, but this time it's how do I know if the clay I got will be 'earthenware' or 'stoneware' - what is the difference at the ground level? I know I'm gonna have to test fire to each temp, but what am I looking for with each fire and are there clues what might be what before I get to the kiln? V:) Link to comment Share on other sites More sharing options...
Babs Posted November 11, 2013 Report Share Posted November 11, 2013 Yeh, and you might want to fire measured test bars to note the shrinkage. What price can you now put on these limited edition pots?? "Clay and Glazes forthe Potter" Daniel Rhodes, Pitman Publishing ISBN 027300218 has a good section on mining and preparing clay for potting. A fairly old text but still useful. Link to comment Share on other sites More sharing options...
Ben Posted November 11, 2013 Report Share Posted November 11, 2013 I've heard this type cay called marl. Link to comment Share on other sites More sharing options...
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