Vince Pitelka on wed 26 jun 96
I have received a number of posts from people who have fired burnished wares up
to cone 08 and higher. Perhaps I am being too cautious in my own practice, but
as I said, we have had a number of burnished pots slip into our normal
bisque-firings, and the burnishing has been ruined. Perhaps some of what is
happening here is that different people seek different degrees of shine. It is
true that almost any burnished finish fired to a higher temperature will still
give a silky texture that is very appealing, but that is different from the
classical burnished surface. When we burnish, we usually go for the glassy
ultra-high gloss, and it is that gloss that seems to be diminished by bisquing
much higher than cone 018. If the ultra-high gloss (which is different from
any gloss which is obtainable with conventional glazes) is there in the bone
dry pot, and if the pot shrinks AT ALL in the bisque, then the shine will
diminish or even dissappear.
I have tried lots of different approaches to burnishing, and in my Ancient Clay
workshop last week we came up with the best yet. I used redart terra sig
rather than a plain redart slip for burnishing. The sig was applied to
bone-dry, sanded pots. Apply several coats of terra sig, and when the surface
moisture had soaked in apply a very thin smear coat of lard. This was the real
thing, from a local pig farmer. I expect the store-bought kind will work, but
I have been told that the real thing, rendered on the farm, is best. I also
understand that shortening and vegetable oils will not work as well, and that
has certainly been my experience. After applying the thin smear coat of lard,
burnish in a normal fashion. If you burnish thoroughly and properly, the
results will be shiny enough to see your reflection. Try this, and fire it to
whatever bisque temp you wish, and let us know what happens.
- Vince
Vince Pitelka - wkp0067@tntech.edu
Appalachian Center for Crafts, Smithville, TN
William Amsterlaw on thu 27 jun 96
On Wed, 26 Jun 1996 Vince Petelka wrote:
> In my own teaching and practice I have always considered a liquid clay
decorating or coating mixture a slip if it is made for application to wet or
leather-hard greenware. I have considered such a mixture an engobe if it is
made for application to bone-dry or bisqued ware.
....
> When we burnish, we usually go for the glassy ultra-high gloss, and it is
that gloss that seems to be diminished by bisquing much higher than cone 018.
If the ultra-high gloss (which is different from any gloss which is obtainable
with conventional glazes) is there in the bone dry pot, and if the pot shrinks
AT ALL in the bisque, then the shine will diminish or even dissappear. <
Vince and others:
Have you ever tried getting the clay to shrink BEFORE burnishing?
Specifically, what if you were to bisque to 08 or higher, THEN apply
several coats of engobe to the bisqueware, and THEN burnish the engobe
before refiring? You might then achieve a high-gloss burnished pot
that is more durable than one fired to only 018. What do you think?
Is it possible to burnish an engobe applied to bisque to a high
gloss?
- Bill Amsterlaw
Plattsburgh, NY
sharon wetherby on thu 27 jun 96
William Amsterlaw wrote:
>
> ----------------------------Original message----------------------------
> On Wed, 26 Jun 1996 Vince Petelka wrote:
>
> > In my own teaching and practice I have always considered a liquid clay
> decorating or coating mixture a slip if it is made for application to wet or
> leather-hard greenware. I have considered such a mixture an engobe if it is
> made for application to bone-dry or bisqued ware.
> ...
> > When we burnish, we usually go for the glassy ultra-high gloss, and it is
> that gloss that seems to be diminished by bisquing much higher than cone 018.
> If the ultra-high gloss (which is different from any gloss which is obtainable
> with conventional glazes) is there in the bone dry pot, and if the pot shrinks
> AT ALL in the bisque, then the shine will diminish or even dissappear. <
>
> Vince and others:
>
> Have you ever tried getting the clay to shrink BEFORE burnishing?
> Specifically, what if you were to bisque to 08 or higher, THEN apply
> several coats of engobe to the bisqueware, and THEN burnish the engobe
> before refiring? You might then achieve a high-gloss burnished pot
> that is more durable than one fired to only 018. What do you think?
> Is it possible to burnish an engobe applied to bisque to a high
> gloss?
>
> - Bill Amsterlaw
> Plattsburgh, NY---------
Our pottery group hosted a Randy Brodnax workshop, in which he
demonstrated several ways to raku burnished pots. Randy applies the
following slip to bisque pots:
1 1/2 cup ball clay
1 1/2 cup EPK kaolin
2 tablespoons calgon powder
20 cups water
He applies this in 2 or 3 thin coats and burnishes the surface with an
old shoe brush or paper towels, etc. Some pots were then wrapped in
toilet tissue, placed in a sealable metal tin, then raku'd (for about
half an hour or more - sorry I don't know to what temperature). You'll
have to experiment.
Other pots were raku fired until they appeared to have a silky white
skin. Then we removed them and set them on a pad of sawdust; dropped
strands of horsehair on them; then lightly fumed them with ferric
chloride (I know this is strong; we worn rubber gloves and stayed
upwind).
Both these processes were successful.
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