glazenerd Posted January 20, 2022 Report Share Posted January 20, 2022 12 minutes ago, Alyosha said: Hi @glazenerd, Indeed I’ve fired the clay by guess to around 800 Cº , it came out good although feels slightly underfired compared to high temp grès. I was told it could be fired to 900Cº. I wonder now if it could stand a proper cone 04. Can I add alumina to it as I did with sand ? When you mean the clay could stay suspended, could I then make Terra Sig from without any deflocculante, with a suffisant amount of water at the right ph ? At this point: I would brush on the Terra Sig you have made: and see how it works after burnishing/polishing it. My "guess" in comparing it to other clays with the same characteristics: you have something close to hectorite. ( 0.05 to 0.15 micron particle size). As a comparision: OM4 ball clay is used extensively in the USA for Terra Sig: the median particle size is 0.52 microns ( if memory serves) about 30% is larger, and 20% is smaller. You see visible sedimentation lines because of the particle distribution: potters are after the 20% super fine particle size. Add kaolin: which is 37% alumina if you want to spike cone values (firing temperature) start at 10% Due to the natural calcium, potassium, and magnesium levels of your clay: the natural PH will be alkaline. There is a simple premise in clay chemistry: alkalinity = deflocculation= plasticity/suspension. Acidity = flocculation/ sedimentation. Yes, I think this clay will stay suspended without adding deflocculants. To get suspension: start by mixing in warm water to get suspension going.(Temperature also plays a roll in particle suspension). Tom Link to comment Share on other sites More sharing options...
Min Posted January 20, 2022 Report Share Posted January 20, 2022 If you do a small test amount without using contaminated water and really accurately measured soda ash and sodium silicate and you still aren’t getting separation after 20 hours of undisturbed settling I would use a purchased dry clay instead, if you have a ball clay or a kaolin for use in your glazes that would be a simple thing to try. Link to comment Share on other sites More sharing options...
Alyosha Posted January 20, 2022 Author Report Share Posted January 20, 2022 Thank you @Min, @glazenerdfor all this precious information, I’m learning alot. I have some doubt about polishing and burnishing as to what shine to expect, I have never seen an example by a potter. I’ll give it multiple tries. Link to comment Share on other sites More sharing options...
Alyosha Posted January 20, 2022 Author Report Share Posted January 20, 2022 The hectorite here is called the green marl of Romainville, there are also some blue marl which is on a deeper layer Link to comment Share on other sites More sharing options...
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