The clay was never lost
Everything trimmed off a pot, washed off your hands or scraped off a bat is still clay. Nothing about reclaim recovers it — it was never gone. What reclaim does is move water: in, to make the scrap mixable, and then out again, to make it wedgeable. That is why the yield line on the page is trustworthy and the drying lines are estimates.
With the defaults, 30 lb of bone dry trimmings and 40 lb of slop at 65 percent water give 44 lb of clay. Throw out 8 percent for grit and plaster chips and 40.5 lb is left. At 22 percent water that comes back as 51.9 lb of wedgeable clay, which is two bags and a bit at 25 lb a bag.
Four gallons in, four and a half gallons out
Slaking that 40.5 lb down to a 55 percent slurry needs 49.5 lb of water in it. The slop brought 23.9 lb along already, so you add 25.6 lb — a little over three gallons. Then wedgeable clay only holds 11.4 lb of water, so 38.1 lb has to leave again. That is four and a half gallons of water to evaporate off a plaster bat.
At 1.6 lb per square foot per day on six square feet of bat, that is just under four days. If you want it back in two days you need 11.9 square feet of bat, which is roughly double what the defaults assume. This is the step that surprises people who thought reclaim was a bucket and an afternoon.
The argument about whether it pays
51.9 lb of clay at 22 dollars for a 25 lb bag is 45.67 dollars of new clay not bought. The default 90 minutes of collecting, slaking, spreading, turning and wedging works out at a break-even of 30.45 dollars an hour. Below that, reclaim wins on money alone; above it, buying wins.
Almost everybody reclaims regardless, and the reasons are sound ones the arithmetic cannot see. The scrap has to go somewhere and a bin is not free either. The reclaimed body is the one you already know how to throw. And an hour spent wedging in the evening is often not an hour that would otherwise have earned anything. What the number is genuinely good for is the opposite decision: whether to buy a pugmill, or to pay somebody else to do it.
Plaster is the thing to be careful about
Grit and a bit of grog do nothing much. A chip of plaster does. It goes through the slaking invisibly, survives the wedging, ends up in a wall, and pops out of that wall in the kiln or weeks later on a shelf. By then the batch it came from has been made into thirty pots. That is the entire reason the rejected share is a field and why studios that use both materials keep the buckets, the tools and preferably the benches apart.
Dry scrap is where the dust is
Reclaim is the one process in a pottery that handles bone dry clay by the bucketful, which makes it the process where respirable silica most easily gets into the air. That is stated here because it is true and because it is the honest counterweight to a page that otherwise makes reclaim sound like free clay. It is not a procedure and this page does not give one.
Questions people ask
How much clay do I get back from reclaim?
Effectively all of it, less whatever you throw out for contamination. Clay is not destroyed by trimming or by being washed off your hands, so 30 lb of dry scrap plus 40 lb of slop at 65 percent water is 44 lb of clay, and after an 8 percent rejection it comes back as about 52 lb of wedgeable clay at 22 percent water. The uncertainty in reclaim is all in the water and the time, not the yield.
How long does clay take to dry on a plaster bat?
It depends on how much water has to leave and how much bat you have. With the defaults, 38 lb of water has to evaporate, and six square feet of bat pulling 1.6 lb per square foot a day takes four days. Doubling the bat area halves the time. The evaporation rate is the number to measure in your own room, because humidity moves it a long way.
Is reclaiming clay worth the time?
The page gives you a break-even hourly rate rather than an opinion. With the defaults it is 30.45 dollars an hour: 51.9 lb of clay worth 45.67 dollars against 90 minutes of work. Below that rate reclaim pays on money alone. Most studios reclaim above it too, because the scrap needs disposing of anyway and the time often is not time that would have earned.
How much water do I add to slake dry clay?
Enough to reach the water content you want to mix at, less whatever is already in the slop. Slaking 40.5 lb of clay to a 55 percent slurry takes 49.5 lb of water in total; the slop already carried 23.9, so you add 25.6 — about three gallons. Then almost four and a half gallons has to come back out again before it is wedgeable, which is the part of the job that takes days.
What ruins a batch of reclaim?
Plaster, more than anything else. A chip goes through slaking and wedging without being seen, ends up in a wall, and pops later. Glaze-contaminated scrap and a different clay body mixed in are the other two. None of them can be detected in a bucket, which is why the rejected share on the form is a judgement you make about your own scrap rather than something a calculator can work out.