Simon77 Posted July 5 Report Share Posted July 5 (edited) Hi all, i have a whitish slightly grayish color clay that is very fine and does not have any aesthetics faults when fired it just looks fine no cracks nothing but when you handle the clay it crumbles and you can easily press and turns back to dust, Little bit about the clay: it has a high amount of very fine mica particles, tried bisquing it up to 1160 celsius and still doesnt vitrify. The color when it fires is faint creamy white and higher temperatures it has a tan to deeper creamy color. Also The clay settles fast in water to the bottom and its very fine. One interresting thing about the clay tho is that when fired to rooughly 4-500 celsius it turns reasonably hard but and waterproof but can still scratch into it. beyond this temperature it just turns to crumbs and dust when handled. What could cause such a behaviour why doesnt it vitrify? And why does it harden at 4-500 celsius and not beyond it? It has been purified many times so its ultrafine, i just dont get it , i have a feeling this is still good clay but dont know how to correct it. Thank you for any help!!! Edited July 5 by Simon77 Quote Link to comment Share on other sites More sharing options...
Min Posted July 5 Report Share Posted July 5 Sounds like it is low in flux. Typically claybodies use sodium and or potassium as fluxes in mid and highfire. Sintering usually starts in the 500C range, after sintering the clay shouldn't slake down in water. Callie Beller Diesel 1 Quote Link to comment Share on other sites More sharing options...
Mark C. Posted July 5 Report Share Posted July 5 Many wild clays are not suitable for ceramics without lots of additives Quote Link to comment Share on other sites More sharing options...
Simon77 Posted July 6 Author Report Share Posted July 6 16 hours ago, Min said: Sounds like it is low in flux. Typically claybodies use sodium and or potassium as fluxes in mid and highfire. Sintering usually starts in the 500C range, after sintering the clay shouldn't slake down in water. Just looked around for fluxes and price wise it comes to the same price if you were to buy clay from the arts store. What are some cheap sources of fluxes? Wood ash? Cheers for everyones input. Thanks Min. Thanks Mark C. Hulk 1 Quote Link to comment Share on other sites More sharing options...
Min Posted July 6 Report Share Posted July 6 Wood ash is going to add mostly calcium along with assorted other oxides. If you do try it I would wash the ash first so it isn't as caustic. I'ld be looking at feldspars instead. There are a number of threads on the forum about found/wild clay. One thread here: https://community.ceramicartsdaily.org/topic/30793-wild-clay-processing/ Quote Link to comment Share on other sites More sharing options...
Mark C. Posted July 6 Report Share Posted July 6 In collage I turned a local clay inmto a high fire (2400 degree) throwing body-it was a ton of testing and big work Yes buying clay at a art store is in my mind way easier and cheaper. The reason to use local clay is one is hell bent on for aesthetics or other reasons Kelly in AK 1 Quote Link to comment Share on other sites More sharing options...
Kelly in AK Posted July 7 Report Share Posted July 7 (edited) Could this be from a large amount of calcium in the clay? See: https://www.floridamuseum.ufl.edu/ceramiclab/blog/calcium-in-pottery/ And a quote from another website: “Limestone is a contaminant for clay that above 125 μm can cause expansion and consequently cracks.” (125 μm correlates to around 120 mesh, that’s pretty fine) That’s from: https://www.intechopen.com/chapters/72560 Edited July 7 by Kelly in AK Min 1 Quote Link to comment Share on other sites More sharing options...
Simon77 Posted July 7 Author Report Share Posted July 7 1 hour ago, Kelly in AK said: Could this be from a large amount of calcium in the clay? See: https://www.floridamuseum.ufl.edu/ceramiclab/blog/calcium-in-pottery/ And a quote from another website: “Limestone is a contaminant for clay that above 125 μm can cause expansion and consequently cracks.” (125 μm correlates to around 120 mesh, that’s pretty fine) That’s from: https://www.intechopen.com/chapters/72560 You could be right, this area is an ancient riverbed with lots of tiny shells in it which could be worn down to microscopic levels by the flow of the river, along with too much nano size mica particles in the clay as it sparkles like crazy. Its impossible to wash out. Still thinking about how to amend the clay because it doesnt crack even if its abruptly heated with a torch probably because of the plenty of mica in it. It probably also has a lot of alumina in it aswell as the area is known for kaolin deposits, so it seems this clay is also highly refractory, but the too much calcium content and mica content is preventing vitrification. In my opinion as of now. Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted July 7 Report Share Posted July 7 Is this your first time working with wild clay? Typically, what settles out, IS NOT used. Instead, it's what stays suspended that's used. (After the excess water has been allowed to evaporate.) What settles out, seemingly wherever wild clay is processed, is fine sand. Once this has been separated out, the clay slurry is then screened to remove even more sand and debris. The slurry is then allowed to dry/stiffen. Its a tedious process but it is fun. (And it takes forever.) I dug up some clay in the back yard, in high school, and after a few washings I had a really nice "terra cota" colored clay. It didn't throw worth a darn but I made some sweet pinch pots with it. PeterH, Kelly in AK and Min 3 Quote Link to comment Share on other sites More sharing options...
Kelly in AK Posted July 7 Report Share Posted July 7 It seems your clay is quite refractory, but reducing the (assumed) calcium content will be a chore. As @Jeff Longtin said, mixing it with a lot of water and discarding the dregs could help. The larger particles and non plastics will settle out first. Takes patience. Another thought is to find a cleaner seam of material to pick. I read a field test for calcium is to put drops of vinegar or muriatic acid on the clay and see if it fizzes. This is also a fun read: https://digitalfire.com/material/limestone I’m curious to know how your fired samples behave submerged in water. Min 1 Quote Link to comment Share on other sites More sharing options...
Babs Posted July 8 Report Share Posted July 8 On 7/5/2024 at 10:28 PM, Simon77 said: Hi all, i have a whitish slightly grayish color clay that is very fine and does not have any aesthetics faults when fired it just looks fine no cracks nothing but when you handle the clay it crumbles and you can easily press and turns back to dust, Little bit about the clay: it has a high amount of very fine mica particles, tried bisquing it up to 1160 celsius and still doesnt vitrify. The color when it fires is faint creamy white and higher temperatures it has a tan to deeper creamy color. Also The clay settles fast in water to the bottom and its very fine. One interresting thing about the clay tho is that when fired to rooughly 4-500 celsius it turns reasonably hard but and waterproof but can still scratch into it. beyond this temperature it just turns to crumbs and dust when handled. What could cause such a behaviour why doesnt it vitrify? And why does it harden at 4-500 celsius and not beyond it? It has been purified many times so its ultrafine, i just dont get it , i have a feeling this is still good clay but dont know how to correct it. Thank you for any help!!! @glazenerd would possibly be a big help with this if he is still visiting these forums. Quote Link to comment Share on other sites More sharing options...
Simon77 Posted July 9 Author Report Share Posted July 9 Thank you all for all your responses! It is immense help with the 360 degree opinions. I will do more tests, refining, trying to add fluxes, or just firing even higher as it is, i will share my findings for what works. Thank you all again for your inputs! Hulk 1 Quote Link to comment Share on other sites More sharing options...
Simon77 Posted July 9 Author Report Share Posted July 9 On 7/7/2024 at 1:06 PM, Jeff Longtin said: Is this your first time working with wild clay? Typically, what settles out, IS NOT used. Instead, it's what stays suspended that's used. (After the excess water has been allowed to evaporate.) What settles out, seemingly wherever wild clay is processed, is fine sand. Once this has been separated out, the clay slurry is then screened to remove even more sand and debris. The slurry is then allowed to dry/stiffen. Its a tedious process but it is fun. (And it takes forever.) I dug up some clay in the back yard, in high school, and after a few washings I had a really nice "terra cota" colored clay. It didn't throw worth a darn but I made some sweet pinch pots with it. It is my first time yes, but i got the idea to just collect the colloidal particles that stay suspended, did that like 4 times pouring from bucket to bucket, left the sand on the bottom threw it out, ended up with a very fine clay. Quote Link to comment Share on other sites More sharing options...
Simon77 Posted July 9 Author Report Share Posted July 9 On 7/7/2024 at 10:07 PM, Kelly in AK said: It seems your clay is quite refractory, but reducing the (assumed) calcium content will be a chore. As @Jeff Longtin said, mixing it with a lot of water and discarding the dregs could help. The larger particles and non plastics will settle out first. Takes patience. Another thought is to find a cleaner seam of material to pick. I read a field test for calcium is to put drops of vinegar or muriatic acid on the clay and see if it fizzes. This is also a fun read: https://digitalfire.com/material/limestone I’m curious to know how your fired samples behave submerged in water. Thank you for the idea, will try the fizz test Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.