Thixotropic Clay

[Kelly in AK]

I’m wondering if anyone has ideas for fixing thixotropic clay. 

My local clay has this property and I’ve been able to improve it by adding 1% Veegum and 20% Lincoln 60. Epsom salts helps, but it doesn’t last. I’ve also used just Veegum at 1-1/2 to 2%. 

None of those additions make it go away completely.

I’m hesitant to increase the Veegum in spite of the miraculous improvement it makes. The clay takes much longer to dry and I have to take a lot more care to prevent cracks.

So I’m asking to see if anyone has thoughts or ideas on this, in case I’m missing some remedy I haven’t considered. 

[Babs]

2 hours ago, Kelly in AK said:

I’m wondering if anyone has ideas for fixing thixotropic clay. 

My local clay has this property and I’ve been able to improve it by adding 1% Veegum and 20% Lincoln 60. Epsom salts helps, but it doesn’t last. I’ve also used just Veegum at 1-1/2 to 2%. 

None of those additions make it go away completely.

I’m hesitant to increase the Veegum in spite of the miraculous improvement it makes. The clay takes much longer to dry and I have to take a lot more care to prevent cracks.

So I’m asking to see if anyone has thoughts or ideas on this, in case I’m missing some remedy I haven’t considered. 

Maybe pm @glazenerd.

[Min]

@Kelly in AK, how much epsom salts are you adding and how long does your clay sit before you throw it? Thinking the clay is probably high in sodium and it's causing the clay to be fairly alkaline, adding the epsom salts should (in theory) counteract that. I could see that over time as more sodium gets involved the effect of the epsom salts would diminish. My hunch would be to make your found clay into a slurry with the epsom salts then dry it out and wedge it up then without leaving it sit for months. Since you live in Alaska and process your clay on your driveway I'm guessing this would be easier said than done.

Edited September 13, 2022 by Min
added a thought

[Kelly in AK]

I feel like your hunch is spot on Min. I’m constantly refining my approach to optimize this clay, from picking it out of the ground, to adjusting the firing schedule, and everything in between. It’s a long game. Keeps me engaged. 

I used to use 0.25% Epsom salts and it certainly made a difference. I tried adding more but got some scumming on the bisque ware and that turned me off.

Because I only mix clay in the summer some of it sits for as long as eight months before I use it. The longer it sits, the more it reverts to thixotropic. After I tried Veegum I omitted the Epsom salts because it worked so much better (still inferior to a nice plastic commercial clay body though). I may rethink that and include Epsom salts in the next batch.

Another thought is that I can store it mixed in slip form and put in Epsom salts as I go. Several one-hundred pound batches through the winter rather than 500 pounds wedged and packed away in September. That way it doesn’t sit long enough to change the ph too much. My back would probably appreciate that too. 

[Min]

11 hours ago, Kelly in AK said:

Another thought is that I can store it mixed in slip form and put in Epsom salts as I go. Several one-hundred pound batches through the winter rather than 500 pounds wedged and packed away in September. That way it doesn’t sit long enough to change the ph too much. My back would probably appreciate that too. 

This sounds like a good idea. Have you tried bentonite instead of Veegum? It would be far less expensive even though you would use at least double the amount.

[Kelly in AK]

I haven’t tried bentonite yet, I may sometime. 

[kande04]

I'm a little late here, but was just throwing with my thixotropic clay and got the bright idea that maybe I should do an internet search to see if there might be a reasonably easy way to fix it.  I already tried Bentonite, and that just made it shrink more so I stopped.  Someone also suggested I add about 15% kaolin, ball clay, silica, feldspar, and maybe one other (I can look that up if anyone wants to know) and then adjust the amounts after testing.  I tried that and it might help, although my clay is so variable (before additions) that I'm not sure if the improved results were because it was better clay, or the additions helped?  Also, if I'm going to add that much other stuff I'm not sure there's much advantage to using wild clay?

But anyway, something I tried today that I haven't before, is I threw with a sponge in my hand, and that really helped. I'm reasonably happy with the clay once it's fired, although it certainly isn't as easy to dry, glaze, and fire as the commercial clay bodies I was using, but the convenience of not having to make a 2 hour round trip to pick up clay, and the price may make the extra effort worth it.

[kande04]

Also, if it's a pH problem, have you tried vinegar?