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How fast does your reclaim settle?

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I am curious and want to do a bit of a straw poll.

Tl;dr, does your reclaim settle out faster if you have soft water vs hard, or is it more of a slurry density thing?


The teaching studio I work at has been doing their own reclaim, and we’ve noticed that our reclaim takes a really long time to settle out. Like, months if the buckets are left alone. We’re using 25 gallon buckets on wheels, and trimmings, dead pieces and throwing slop go in. Being a teaching studio, we get a lot more throwing bucket water than discards or dry material. While we can siphon some water off over a period of days, the amount we can take caps when the bucket is down to about half to 2/3 full. There’s usually about 1/4-1/3 solid material, and a giant layer of slip that can vary in density, before we start adjusting anything.

We also have heckin’ hard water where I’m at, and is very high in calcium carbonate (120-250mg/l, depending on the time of year). Our water source is a river, and flocculants are added at the start of the water treatment cycle to get rid of sediment. While most of the aluminum based flocculant is removed and calcium carbonate is mostly insoluble, the possibility of calcium ions adding some small flocculation effect does exist. 

Since it’s not exactly practical to get folks to throw with distilled water, I’m mostly stuck with adding a big bag of clay dry mix to the reclaim to dry out the slop to a consistency where I can spread it on the drying racks, and that works pretty good. So I’m not looking for problem solving. 

So my question is:

If you have soft water or use rainwater in your studio, does your reclaim sludge stay suspended for a long time, or is it just us?


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We had soft water at the last house.
Some clays settle faster than others has been my observation, but every clay I've tried will show some clear at the top within a reasonable time.
How much clear, that's variable; the ones that have just a few inches of clear at the top take much much longer to separate any further.

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a story which has information about a clay in water: 
long long ago, but not to far away, I was still assigned to the refinery when one of the plant cooling systems was changed from deep clean cold water wells to river water that had a small but visible amount of yellow river clay suspended.   Shortly after the switch to river water, the plant heat exchangers began to plug with clay and the exchangers had to go off line to be cleaned (not an easy or low cost task). 

The lab was trying to find why the plugging was taking place and they were not finding anything about why the system was being plugged.  

A lab technician had put a bottle of the river water in the window to watch it over time.  After month nothing had changed, the clay in the bottle of water was still suspended.  Later on, someone decided to clean the window shelf and set the bottle of river water into the sink which had some warm water flowing through.  When the someone picked up the bottle to it back to the window shelf,   he noted that all the clay was now at the bottom of the bottle and the water was clear; and he came upstairs to tell me what he had found.  

my recommendation is to heat the slop water a little bit and see what happens.
if your clays are like my south Texas river clays, boiling is probably not needed. 


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@Magnolia Mud Research you might be on to something there. The weather has started warming up, so we’ve been opening the back roller door to allow for more evaporation off the reclaim barrels. On the days we’ve been ove 20 degrees or so (that’s 68 for you fareneheit heathens), there’s been a noticeably larger amount of clear water on top of the barrels. It was only an inch or so, but it was noticeable. The warehouse bay’s thermostat is set to 19, but it feels cooler than that. 

So given that I have 2 options available for possibly heating some slip: a metal bowl in the test kiln or a plastic container in the microwave, which one is going to make my boss question my sanity the least? I’ll let you know. 

@High Bridge Pottery this might tie in to some casting slip principles too. Don’t slip densities change with temperature? I can’t remember what the range is though. 

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On 5/21/2024 at 10:07 PM, Callie Beller Diesel said:

So given that I have 2 options available for possibly heating some slip: a metal bowl in the test kiln or a plastic container in the microwave, which one is going to make my boss question my sanity the least? I’ll let you know. 

Maybe a milk bottle full of reclaim in a bucket of hot water would be less obtrusive? And defendable as trying to confirm @Magnolia Mud Research's observations.

... with some sort of waterproof under-bucket heated mat as a potential permanent solution.

PS I'm bemused about the physics/chemistry behind the behaviour. For example you might expect any low temperature based changes to slow down settling not to stop it.

However Brownian motion may be relevant.
The 20-hour settling time may seem arbitrary, but it's not. I am grateful to student Rob Williamson at U-Mass for helping to determine the ideal settling time. There are several forces at work in this deflocculated mix. The deflocculant introduces same electrical charges to particles in aqueous suspension, causing them to repel one another and stay in suspension longer. Also, there is ever-present atomic vibration which causes particles in liquids to naturally disperse. Working against these forces is gravity, causing particles to settle out. At 20 hours, in a deflocculated slip of the correct specific gravity, gravity has caused all the heavier particles to settle out, while atomic vibration and the repelling forces caused by deflocculation keep the finest particles (generally those less than one micron - 1/1000 of a mm) in suspension.


1) Viscosity might changing by a factor of 2 or so.

2) Electrical double layer effects can change with temperature.

Edited by PeterH
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