Jonathan Kaplan on sat 7 mar 98
Jan Walker asked for an answer about ball milling....why commercial mills
are so expensive and why ball mill at all.....
Yes its true that for he most part, the materials we purchase to make glaze
are finely ground. Once they become part of a glaze mixture, a suspension
of materials in an aqueous solution, one would expect that these materials
and their respective particles are uniformly distributed. For the most
part, yes. But it might be worthwhile to think about how these materials
melt in the kiln, how they sit on the surface of the ware as they melt, and
what influences an optimum glaze surface. There's no need for lengthy
chemistry and physics here. Suffice it to say that it is the grind of these
materials, the nature of glass structure relative to the grind that plays a
very important part to optimum surface development. For instance, lets say
you go to Feldspar mine in Spruce Pine NC and get some crude feldspar
before it is selectively processed. And lets further say you hand grind it
in your morter and pestle or other some such device. Add some water, make a
crude solution and apply it and fire it. Chances are that the surface will
be rough, perhaps the glass will be undeveloped. Run the same test with
some processed spar, and the results will be dramatically different(same
temperature). Voila, illustrating that the grind of the material is
directly responsible for the optimum surface development, the melt. Sure if
you fire any material to a hot enough temperature it will flow, but that's
not the point here. It is the action of milling that effects the particle
size and hence the melt, the fluidity of the melt, etc etc.
So ball milling renders a solution more homogeneous by the milling action
of the grinding media, the amount of charge in the mill, the speed of
rotation in the mill, and the time the solution is in the mill being
processed. There is an optimum balance between all these factors relative
to the glaze. Too much milling will result in a glaze solution that has
absolutely no surface tension whatsoever and will run off the pot.
Do we need to ball mill all our glazes? Probably not, and as most on the
list who make glazes have seen that a simple jiffy mixer followed by some
selective seiving will produce a glaze that for the most part, will work
well. But, we also know that all glazes are not the same and perhaps some
may require ball milling to produce the proper effect. Ball milling is also
one of the things that may be out of reach for studio potters in that a
one gallon ball mill jar is faily heavy and large, the mill needed to turn
it is substantial, and if you have a 30 gallon batch, you gonna mill 30
times? Plus that one gallon jar doesn't hold one gallon. And on it goes.
So we also need to get some terminology right.
What we often refer to as "ball mills" is kind of generic. Refers to a
rotating jar with a charge of grinding material and stuff to grind up.
According to US Stoneware (one of the largest producers of mills) ball
mills of their manufacture range from 12-210 gallon capacity and ar quite
substantial pieces of equipment, both in the size (physical footprint) and
price for most potters. These are some hefty pieces of equipment.
What is more akin to what we use are called "jar mills" and can be as
simple as one jar, multiple jars on one tier, or on multiple tiers, short
rollers or long rollers, etc.etc. These can be belt driven, chain driven,
one speed or multiple/variable speeds. More affordable.
Why so expensive? The simple answer is just "because." These are industrial
manufactured devices and I am sure carry the manufacturer's hefty overhead,
especially for items like liability insurance and a myriad of others. In
concept, yes, these are simple devices and are well within the scope of
shop built equipment if you need one. I would posit that most studio
potters don't need a jar mill for their glazes unless the specific glaze is
extremely problematic and can be beneficiated by selective milling. Val
suggests that terra sigs should be milled, This is a specific application
in which a mill could be and probably is very useful.
Commercially available mixed glazes are often milled to proper uniformity
and would probably only require periodic sieving.
I have seen and used some jar mills that are available. The Amoco unit
works fine, the Shimpo mill/potters wheel attatchment is funky and not what
I would use if the case warrants. The small units from US Stoneware are the
Cadillacs and well worth the investment. There are many many sources for
used mills and jars, so it is really not necessary to purchase a new one.
(and again, the usual disclaimers apply)
Case in point. I purchased a used "Ohio Kilns" brand variable speed 2
tiered 48" long jar mill with lotsa jars and media some time ago to mill my
06-04 majolica glazes. Rebuilt the unit with new bearings, rollers, etc.
Works fine, Could use a full horse motor. Made my glazes much better and
certainly helped disperse all the glaze additives. Was a pretty involved
process from a time point
of view. Don't use it any more, and yes, it is for sale, and if anyone is
interested, I'm a pretty motived seller, so post me personally so as not to
clutter the list.
Jonathan Kaplan, president email@example.com
Ceramic Design Group Ltd./Production Services
PO Box 775112
Steamboat Springs CO 80477
(USPS deliveries only)
1280 13th Street Unit 13
Steamboat Springs CO 80487
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(970) 879-9139*voice and fax