The procedure described below by Andy is exactly right.
If memory serves, the official 'Sunday' name for this particle size sorting
by differential settlement in water is 'Levigation', and the Romans did this
on a big scale when making Arretine, Samian and other terra sigillata. They
had big tanks full of water especially for the purpose.
Winnowing of grain is fundamentally the same process, but using air rather
than water as the working fluid.
----- Original Message -----
From: "Andy Holland" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, June 08, 2009 2:38 PM
Subject: Re: [BRITARCH] Clay Mines, clay querns and neolithic sieves
The easiest way is to mix your now crushed mixture into a lot of water
in a big bowl or similar, stir it round and then leave it to settle.
Gently drain the water off once it has settled and (assuming you put
enough mix into it in the first place) it should now be sorted with the
big gritty bits being at the very bottom.
Once it dries out a bit you can then turn it out and scrape the gritty
rubbish off the bottom.
But remember you need a bit of finer gritty stuff to act as temper
(unless you use something else like grog (ground up old pottery).
Water settling is the easiest way to get good sorting of clay also if
you can get it to a nice fine paste like slurry then you can pour it
into moulds to create moulded pottery like samian ware! Or use the
slurry as a slip.
Hope this helps
From: British archaeology discussion list
[mailto:[log in to unmask]] On Behalf Of Michael Haseler
Sent: 08 June 2009 13:57
To: [log in to unmask]
Subject: Clay Mines, clay querns and neolithic sieves
The kids were off school, they wanted something to do, the pottery clay
that came with the plastic pottery wheel had run out and I'd finally
found a possible location of a "clay mine": a site of an old pottery.
So, off we went. Pick axes on shoulders in a scene much akin to snow
white and the two dwarfs.
Strange thing, clay. It seems to be everywhere when you don't want it
(usually foot deep mud that clings to boots) but when you go looking for
it, it just seems to disappear.
Eventually on the banks of a stream I found a very thin seem of what
looked like clay hidden under topsoil. But it was full of odd stones,
even what looked like charcoal but was probably slate. But the kids
thoroughly enjoyed using their pick axes whilst I succeeded in avoiding
being poked in the eye by the back swing as I dug out 60kg of "clay" and
then carried it up a slope which suddenly became 10x steeper.
So we left it out to dry for a few days, and then the internet said to
I tried walking on the lumps, I tried using a lump hammer, and
eventually I made very slow progress (with the "help" of two dwarves)
with two pieces of paving slab rubbed one on top of the other in what I
realised was a primitive quern.
But instead of crushing the clay leaving the stones intact, all I
managed was to grind up everything into a very gritty and to be quite
honest highly suspect mass which I then sieved using our kitchen sieve -
which given the impossibility of such an approach for pre-industrial
society clearly meant there must be another way to do this processing
which doesn't involve inhaling a lung full of clay dust.
OK, I know we don't live in an ideal place for clay, and those places
where there are rumours of clay are inhabited by hostile tribes
(Council/private owned property by the Clyde), but it never occurred to
me that a decent supply of clay could be such a valuable asset ... and
I've been looking for a while and I'm fed up of strange looks for people
in excavators as I wonder up to look at their hole in the hope they are
digging in clay!
REMEMBERING THE VAST AMOUNT OF POTTERY FOUND ON MOST ARCHAEOLOGICAL DIGS
- WHICH MUST COME FROM SOMEWHERE - there's very little on "clay mines"
(I mean quarries) on the internet.
1. is there any archaeological evidence for specific sites being clay
"mines"? I mean, they must exist, but as I realised trying to find the
source of clay for the pottery, it probably very quickly gets overgrown.
2. what's the evidence for method(s) people used to process clay for
pottery in pre-industrial times? How many of those querns were being
used to process clay and not grain - or did they use water in some way?
3. Is there such a thing as "stoneless clay" - if not, how did people
get rid of the stones? Or is crushing them in the clay part of the
4. How selective were people in pre-historic times in selecting clay
What I mean is: can all clay be used for pottery? If I randomly went
around every single site of accessible clay around Glasgow, how many
would I have to visit before I found one even half suitable for pottery?