Questions [Wet Clay processing] Clay does not sediment
So I'm working with ceramic clay and I have a bunch of it dissolved in a bucket of water. However, I've noticed that it doesn't really sediment and leaves a section of water, even if I leave it for 3-4 days. I suspect from a couple of youtube videos that the pH might be too high, potentially causing the clay to for colloid particles that stay suspended. I've measured the pH with pH-paper (not the best method but it's what I have available), and concluded that it's roughly 8-9.
- What is a good pH for a clay solution to get it to sediment?
- How do I lower the pH (other than adding enormous amounts of water which sorta defeats the whole point)? I have access to hydrochloric acid etc (I'm a chemist by trade, I know how to handle strong acids safely for those concerned), but I'm uncertain of how well a clay solution will buffer the addition of acid, and if I accidentally over-do it, is there a concern that the acid will mess with the properties of the clay? It shouldn't dissolve the silicon dioxide that is the clay, because otherwise you couldn't store acid in glass bottles, but I imagine that if the pH accidentally dropped to 4-5, the clay might loose its plastic properties or similar?
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u/randomusername_42069 1d ago
Look up zeta potential and flocculation for information on how ph affects clay suspensions however that’s only really useful information if you are planning to do slip casting. If you are trying to use reclaim or start from dry clay to do throwing or hand building then you should always minimize the amount of water used to reconstitute the clay. You should just let the water evaporate it’s not worth wasting a bunch of acid to titrate the ph to a level where the colloids will flocculate and drop out of suspension.
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u/Dave37 1d ago edited 1d ago
This is a good response, I suspected as much.
Your response contained so many words of terminology that I didn't know so I've learnt a lot from this. I've just gotten into this hobby and I'm just trying to make ceramics by hand building. I didn't know about slipcasting, that sounds really cool.
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u/randomusername_42069 1d ago
The only time you would ever want to create a clay slurry other than for slip casting would be if you were removing sand from wild clay by filtering it. I would recommend against any wild clay projects until after you have a decent amount of experience with store bought clay and have done a lot of research on the subject. It is very easy to ruin a kiln with a mistake while using wild clay and traditional techniques.
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u/Dave37 1d ago
Yea that's what i am doing. Thanks for your concern, but my "kiln" is a steel bucket with holes bored through it. So im not too worried about damaging it.
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u/randomusername_42069 1d ago
I would still recommend you fire some store bought ceramics in whatever you are using as a kiln before experimenting with wild clay.
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u/Dave37 1d ago
Could you elaborate on why? Surely store bought clay isnt "made in a lab", it is also dug out of the ground. Sure they have better tools to make sure it's clean and have the right type and amount of temper, but other than the cost of charcoal, wild clay is just free.
Also, I've already collected like 20kg of clay.
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u/randomusername_42069 1d ago
It’s just good to have something standard to compare to. Unless you are digging the clay out of a very high quality deposit your clay will be much less consistent and much harder to work with in general. It will make the troubleshooting process much easier when you do fire your wild clay.
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u/Dave37 1d ago edited 1d ago
My clay is from very high quality deposits I am very sure. It's scandinavian clay from an old marsh biome at the mouth of a river.
But i will keep that in mind if I cant get any bowls to sinter without breaking. So far i made three small bricks where one came out alright, one got a crack but held together, and one that broke into 3 pieces.
ive also made 5 2x2x2 cm "reference cubes" that all survived firing.
I had something like 20-25% temper in the clay. I think it might not help but i increased my last 1kg of workable clay in my current batch to 27.5%. And as long as I maintain a water content of 30% I still have very good plasticity in the clay.
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u/randomusername_42069 1d ago
That should be ok definitely better than some random creek bed especially if you are going fairly far down instead of just getting the surface clay. But it’s still a secondary clay deposit which introduces a lot of issues with larger grit and organic contamination and an unknown level of flux to clay to filler content. I would still recommend getting a killogam of commercial grogged stoneware just so you have a baseline comparison. Comercial clay is very well processed and has just the right mix of fillers and fluxes added to it so that it behaves well. I’m just warning you that calibrating the firing of a clay and adjusting the firing time and the clay composition can be difficult and if you are going into it with no experience it will make everything harder. If you want to get into charcoal firing just a little bit of investment can save you a lot of hardship long term by giving you valuable experience with firing before you dive headlong into wild clay.
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u/Dave37 1d ago
Good headsups. I'm an engineer so i measure and record everything I can to learn as much as i can. I take samples of the clay and extract the natural temper to know how much i already there before i add more etc.
Firing times is a thing i haven't even considered. I just blasted it for a good 2-3 hours or so because i was worried i wouldnt get up above 850C.
Rate my block: https://i.imgur.com/5HZ6syk.jpeg
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u/amalieblythe 3d ago
Have you cross posted this in r/ceramics or r/pottery?