MudPuppy on wed 28 jul 04
Hi there everyone,=20
I have some questions about making and firing/glazing plates.
At the suggestion of my mentor, I am working on dinner plates, thrown on =
a Pure and Simple plate bat.
I'm exploring both forming from a slab placed on the bat, bringing up a =
foot from the slab, and simply centering a ball of wedged clay on the =
bat and actually throwing the form around the bat.
Slabs seem to be easiest and, at lest for now, more consistent.
I'm trying to avoid attaching a coil for a foot, but I may try that too.
Anyway, I have some questions about my methods, as well as basic "plate =
philosophy".
I am using both KPS White Hawk and KPS Porcelian clays, firing in a =
converted hex electric kiln that struggles to fire to a good ^9. I am =
bisquing to about 900 c.
My porcelian plates, which were about 3/8" thick when green, all cracked =
in the bisque. It was my first bisque with the porcelian in it so I may =
simply have to slow down my firing. Or are there things I need to know =
about Porcelian?
Anyway, the plates thrown with the KPS WhiteHawk, which were also much =
thinner, survived fine as did a porcelian bowl.
I am still struggling a little with my kiln's temp, though a combination =
of drilling holes in the shelves and removing the ceramic fiber have =
given me a very even temp, top to bottom ;) I think I was just not =
allowing enough air flow.
The glaze firing went pretty well, except that I had some stuff run alot =
because the glazes were applied thickly.
I also had a small bit of warpage, but not alot.
So I guess my questions are:
Are there rules of thumb for plate thickness and foot depth/width for =
plates?
Are there particular glazing techniques to minimize running, =
particularly on the outside of the plate?
Are there ways to minimize/eliminate warping?
Are there schools of thought, rules, or other sage words for would-be =
plate makers, both regarding technique and aesthetic?
Thanks everyone!
Cathi Newlin, Mercer, Mo
mudpuppy@box49.com
http://www.box49.com
Ron Roy on mon 2 aug 04
Hi Cathi,
Those porcelain plates probably cracked during cool down - when the rims
went through the quartz inversion at 573C. The foot of the ware went
through the quartz inversion a little later. If the cracks were closed
thats what happened - if they are open it is related to how you made the
slabs.
I would recommend you fire your bisque to cone 04 (1050C) which make the
ware much stronger - especially the porcelain - which has a lot of quartz
in it.
Use some thing to keep the plates off the shelf a little - so the bottoms
can cool a bit faster. Make sure you kiln is well sealed up to slow cooling
- especially around the quartz inversion temperature.
Keep the porcelain at the top of the kiln - which cools slower.
Keep the rims a bit thicker and the bottoms a bit thinner to help even out
the cooling.
You can even surround the plates with kiln furniture to slow down the
cooling of the rims.
Firing down from 650C to 550C is an option but should be a last resort.
RR
>My porcelian plates, which were about 3/8" thick when green, all cracked
>in the bisque. It was my first bisque with the porcelian in it so I may
>simply have to slow down my firing. Or are there things I need to know
>about Porcelian?
>Anyway, the plates thrown with the KPS WhiteHawk, which were also much
>thinner, survived fine as did a porcelian bowl.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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