Talbott on wed 5 feb 97
Bill...(and anyone else willing to reply)
I know nothing about pugmills except that I want to buy a Venco 4"
deairing model... We mix our own clay with a Soldner and then do the
wedging thing by hand.... Can you tell me how much difference there is in
the throwing qualities of clay that has been wedged by hand only and clay
that has been through the deairing pugmill and then wedged a little by
hand?
Best Wishes... Marshall
>----------------------------Original message----------------------------
>Hi Randy:
>
>I have a 3.5" Venco deairing pugmill set up so that the vacuum pump and auger
>motor can be turned on or off independently. This machine is tough, safe,
>easy to maintain. I love the thing. It is my friend and helper, taking much
>of the drudgery out maintaining a supply of clay with good working properties.
> It does have certain limitations and idiosyncracies that need to be
>understood.
>
>You can use the pugmill as a multipurpose tool in a relatively low-volume
>studio - but If you plan to put out a high volume of work, you will probably
>want to have a clay mixer or continue to buy pre-mixed clay. You can use a
>pugmill to mix or reclaim clay and get clay that is of good quality - but it
>is a very tedious and inconvenient way to do it. The best way to use a
>pugmill is to help you prepare good clay just before you are ready to use it -
>ie, the thing it does best is do most of the wedging for you.
>
>Some notes:
>
>1. The vacuum is not a useful feature when you are mixing or reclaiming. If
>you are using the pugmill to mix or reclaim clay, you almost always have some
>stuff that is pretty wet that you want to mix with other stuff that is dryer.
>Any time you try to put much wet stuff through, it tends to get sucked up into
>the vacuum chamber ... and if ignored, can fill the chamber and get sucked
>right into the vacuum line. Nils Lou claimed (Clayart 14 Aug 1996) that clay
>that is not de-aired ages faster than vacuum-pugged clay. So if you use the
>pugmill to mix clay that is going to be stored, even if it is not wet stuff,
>it might be best to turn the vacuum off. Then when you are ready to use the
>clay, pug again with vacuum.
>
>2. A pugmill doesn't work very well if the clay is either too wet or too dry.
>If you try to put stuff through that is too dry, it will get hung up in the
>screens which will then need to be taken out and cleaned. If you try to put
>stuff through that is too wet, the mass of slick, wet clay just wants to
>cling to the auger and go round and round rather than pushing forward.
>Therefore, if you get too much wet stuff in the barrel, you need to force some
>dryer stuff down there to push the wet stuff along, and/or you need put your
>weight on the lever to plunge the wet stuff through. With a lot of plunging
>of wet stuff, it is very easy to experience squirt-back ... where you push
>down on the lever and stuff squirts around the plunger and comes back at you.
>None of this is easy or convenient or fast or fun - but it is an aid to
>winding up with a homogenous mass that beats wedging with your feet. It would
>be a lot easier to just throw all this into a Soldner mixer and let the mixer
>do most of the work while you make pots.
>
>3. You can use the pugmill to mix clay from dry ingredients. The best method
>I have found is to thoroughly mix dry ingredients in a wheelbarrow. Then
>artistically pour in the perfect amount of water - usually a lot less than
>your first guess. You can add reclaim to this stuff. Then you smoosh the
>stuff around with your hands to form clumps that you put through the pugmill.
>With a little practice in how much water to add, you can put out clay of good
>quality - but it is not easy or convenient or fast. A mixer would be a better
>tool.
>
>4. Even if you have a deairing pugmill, you will still probably have to do
>some wedging ... or you may lose a lot of pots to s-cracks.
>
>5. Some people prefer to work with clay that is not de-aired ... and some
>people like to wedge. My personal preference is to throw with de-aired clay
>and wedge no more than necessary. Deaired clay seems dramatically more
>plastic and it seems to resist slumping far better than non-deaired clay.
>
>6. No matter what machinery you have to help you, there is still a lot of
>unavoidable drudgery involved in reclaiming waste and maintaining a supply of
>usable clay.
>
>---------
>On 1 Feb 1997 Randy Golly wrote:
>>>
>After reading the pugmill posts I want to know more about if a claymixer or
>a pugmill would work for my one man studio. I am buying commercial clay
>here in Dallas from Trinity Ceramics and am happy with the results. Hate
>reclaiming clay in buckets, then onto plaster bats, the whole process is a
>pain. Would a Soldner Mixer do the job for putting in scrap then remixing
>with some more dry elements to reclaim? Or would a pug do the job better
>by deairing it at the same time, bypassing having to wedge all of the new
>reclaim?
><<
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Bill Amsterlaw on fri 7 feb 97
Hi Marshall Talbott and Craig Martell:
Marshall asked:
>> I know nothing about pugmills except that I want to buy a Venco 4"
deairing model... We mix our own clay with a Soldner and then do the wedging
thing by hand.... Can you tell me how much difference there is in the throwing
qualities of clay that has been wedged by hand only and clay that has been
through the deairing pugmill and then wedged a little by hand? <<
I don't pretend to be any kind of expert in this, have no engineering
background, may need some help describing things I have observed (thanks,
Craig), can only speak from my own experience....
Clay needs to be prepared to perform at its best: Its water content needs to
be within a certain range and you need to homogenize, compact, and deair it.
How good a batch of clay can get is partly a property of the claybody and
partly a property of the methods used to prepare it.
The experienced potter knows by the way the clay responds to his/her touch
how far the clay can be stretched, pulled, bent, or thinned before it will
break or collapse. The best clay holds together well. It can be thinned out
or bent without cracking. You can stretch the overhang of a bowl way out
before it will start to collapse. But you learn to work with good clay and
bad clay. You adapt and make use of what you have. It is my impression that
if you take clay that has never been put through a deairing pugmill and wedge
it until you feel it is wedged well ... a run through a deairing pugmill will
make it better.
Since I can independently control the vacuum and the auger on my pugmill, I
can easily compare clay that has been pugged with or without vacuum. I have
done some tests to try to see what effect the vacuum has on the final product.
For one thing, the vacuum increases the weight of a given volume of clay by
about 6%. I suppose from this you could calculate the volume of air removed
from the clay. When I have the vacuum turned off, the clay that comes out is
"short". If you take a coil of it and bend it, the convex surface of the bend
cracks open. If you stretch the coil, it breaks easily. When you wedge this
clay, it cracks any time it is bent. You can wedge this clay for half an
hour, and it will still be short! If you then run the same clay through the
pugmill with the vacuum turned on, it changes dramatically. You can bend a
coil of the deaired clay this way and that without seeing any cracks. When
you stretch a coil, the clay will taper before it breaks. When you wedge it,
it clings to itself and develops no cracks at all. You might be able to throw
pots with the non-deaired product, but the deaired product is a much better
material to work with.
- Bill Amsterlaw
Plattsburgh, NY
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