Ron Roy on sun 16 dec 01
I realize every one must be getting sick of this subject but I feel we have
lost the essentials or they have never shown up.
Different clays respond to successful joining in different degrees.
There are several factors involved and we have many different requirements
depending on the clays we use, where we live and work and what kind of work
we produce.
Where we live - when and if the heat comes on the air gets drier and clay
dries out faster and more unevenly. If we only make a few things it is more
difficult to dry them the way we usually do to avoid cracking. Production
potters who make many have less of a problem because there is more
evaporation and that slows drying down.
Even turing the heat down in your studio over night can help. Certanly a
humidifier during the heating or cooling seasons will make a huge
difference.
Every clay has a different drying rate - some dry more evenly naturally -
like stoneware with grog and fire clay. Porcelain dries more unevenly as
does any fine grained clay.
Fresh clay cracks more easily then well aged.
We tend to say - this has always worked for me but we don't describe the
circumstances, the type of ware or the clays we use.
In the end we must all figure out what works for us. What I am trying to
say is - don't take anyones word as law on this subject because their
circumstances are probably different from yours. Trying the different
techniques will bring you to the best techniques for you - just do the
experiments and try to control the results so you find the best way for you
- and if you have a generous heart and soul - share the results with us and
include the details.
The books we use are - for various reasons - incomplete in that they
usually advocate one technique or maybe two when in fact there may be many.
The key to successful problem solving is - especially in clay work -
understanding as much as we can about the science of the materials and
techniques we use.
This forum is amazing in the depth of understand it fosters - we should all
try to make an effort to encourage the documentation of the wisdom of so
many. The magazines we read are hungry for this material - there is a
wealth of material that potters need and we have it coming in every day.
RR
>Making a comparison between joints made with deflocculated slip, magic
>water or vinegar without roughing up the surface of either part and joints
>where splash pan slurry and deep scoring is used to roughly join part
>together is like comparing cheese with chalk.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Snail Scott on mon 17 dec 01
At 09:24 PM 12/16/01 -0400, Ron wrote:
>Different clays respond to successful joining in different degrees.
I have often observed this. And, I have a Theory...
Some clay bodies join easily with just a casual,
slapdash effort at luting. Others require heroic
efforts with scoring and slipping, or scrupulous
attention to moisture content.
My favorite clay body for joining (and since I coil-
build, that's a lot of joints) is several clays
plus grog, which I mix myself. It seldom separates
at the joints, even with a fairly haphazard and
loose technique. Most of my preferred clays are of
similar composition and properties. (I like the
IMCO 412 pretty well.)
My least favorite claybodies for joining tend to
be lowfire and fine-grained, with (I suspect) a
high level of non-clay ingredients like fluxes
(feldspar, talc, whatever). They separate at the
slightest provocation even after meticulous joining.
(I like the look of the Claymaker terra cotta, but
it separates at the joints worse than almost any
clay I've used.)
It seems to me that clay bodies with a high clay
content tend to 'stick together' very readily,
while clay bodies with high percentages of other
materials need more effort to achieve a good joint.
I suspect, (but don't actually know for a fact,)
that commercially-formulated earthenware recipes
tend to have more 'other stuff' than typical
stoneware recipes.
Or it may be that certain materials cause this
effect, but not all. (I have my suspicions about
feldspar. It seems to be strongly present in many
clays that join poorly.)
(I am unconvinced that the grog content is actually
relevant. It may merely be a coincidence, and there
may be (I think) simply more groggy stonewares than
earthenwares.(Correlation, not causality, perhaps.)
Ron? (or anyone else,) care to venture an opinion
pro or con?
-Snail
Ron Roy on mon 24 dec 01
Hi Snail,
Well - without having done any specific experiments I can only go on past
experience. My comments are therefore best guesses.
It may not be the feldspar content but rather the plastic(clay) to none
plastic ratio that will determine to some degree how easily clay joins - it
may even be the principal factor.
Perhaps your observation that felspar is a factor may have to do with two
aspects.
High feldspar may have an effect because sodium is present - the more spar
the more chance there would be some sodium solubility and hence some
deflocculation.
The main factor in the high spar scenario just might be - white clays are
harder to melt and there for need more melter - and white clays tend to be
harder to join than darker clays. I think I understand why this is so but I
don't think I can explain it properly. Particle size has a place in the
explanation I am sure.
I have worked with many clays over the years - I don't do a lot of joining
but I do problem solve for many potters and this subject is not something I
have to deal with often. The clays I am responsible for are mostly the
clays I have developed over the years.
One of the rules I set for myself is - use as many different clays in a
recipe as practical - this insured some degree of stability and good
particle size distribution. The group of clays in which I cannot use the
usual number of clays when formulating are the porcelains. They seem to be
harder to join than the stonewares.
RR
>It seems to me that clay bodies with a high clay
>content tend to 'stick together' very readily,
>while clay bodies with high percentages of other
>materials need more effort to achieve a good joint.
>
>Or it may be that certain materials cause this
>effect, but not all. (I have my suspicions about
>feldspar. It seems to be strongly present in many
>clays that join poorly.)
>Snail
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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