Bill Edwards on sat 26 jul 03
Well, some things were learned. Earlier I mentioned
firing a slow ramp speed to 2200F and then allowing to
cool to 1500F and then ramping back up to 010
(1632F+/-)and holding for 30 minutes and then allowing
to cool on its own accord.
The results were additional crystal growth on a visual
scale as well as some loss of gloss as I expected. Not
a terrible drop in gloss but some non the less. A
longer hold time and I would expect some additional
matt effect. The porcelain showed some good color but
I had fears since this was a mixed load of decorative
work and sure enough some small pieces managed to warp
a little. Porcelain is picky if its thin and I did
have some warped pieces with pretty glazes.
This is a 3rd re-arranged firing I have done recently
to check the visual differences and really all I can
say is so far unless you are wanting to matt a gloss
through excessive crystal growth from rutile, boron
and calcia the slow fire method works better for me
using a 12 hour firing cycle give or take. Allow to
cool normally!
I am sure additional durability would be obtained from
this holding process especially if the base was prone
to being closer to a higher temperature maturing
glaze, (Time and Temp both effect a glaze) since the
glaze has to reach full maturity and stablize but lets
not yet leave out fully a well made semi matte glaze
or egg shell glazes that matures well enough to pass
lab reports and was calculated to mature at the range
of temperature we work at or desire. While these
glazes can be produced a multitude of ways, I am
speaking mostly of high clay glazes not barium to
produce the matts. Personally I use very little matte
glaze with exception to outside areas of service ware
or for decorative purposes. Sometimes I make a cup or
chalice which will be glazed up to about 3/4ths an
inch from the rim. The interior and rim area will be
where I use one of my lab tested glazes and of course
where food would be in contact. Of course as Ron and
John and others have said, some glazes are so poorly
devised that over time color loss can happen, cutlery
marks appear, get rid of these types of glazes. The
casserole and dish set I made for myself 6 years ago
is still as bright and new and craze free as it was
the day it came from the kiln, its between a semi matt
and waxy and was lab tested. I expected some glaze
integrity issues over time but these pieces still are
without visual cutlery markings and they see daily
use. All I am saying is there are lots to learn, lots
have been learned and more learning is going on as we
dig deeper into how heat effects glazes and how glazes
can be re-worked to achieve a desirable outcome with
less issues regarding toxicity or loss of durability.
I was firing slow firings back then and apparently
that has helped greatly! So the current information
would tell me to continue slow firing and if I chose
to raise the crystalization up and mute the glossness
I will ramp down and hold unless I chose to use a
glaze that to some may be what is called immature? The
line is thin in that regards since I think there is
some good work going on in slow firing those
particular glazes over a longer period of time even if
not ramping down on each firing. Someone correct me on
this if its out of line terribly! Currently I have to
trust that a lab report is the closest thing to right
as I can get coupled with glaze chemistry software and
countless notes and recipes that I have covered myself
up with over the years. There is still mystery to
explore and I will continue to explore the potential
for all this with each kiln load.
Durability I believe can be had with heat ramping
slowly on the way up and if its crystalization and
more matteness ramp down and hold or use well thought
out glazes formulated between a semi-gloss and waxy
and use them asthetically because in the real world
cutlery usually will mar those surfaces. The drier the
glaze surface the more problems with marking and
certainly there is a durability factor for the most
part based on whats in the glaze and how well it fits
the body. Decorative artists - I do that as well and
believe me I love a dry matte on certain pieces. I
made a purple one time that I should have named sand
paper purple. Never did crawl or have defects but was
a wild one to look at and to touch. A lot has been
said about durability but there is still some
decorative process in our work and the only way to
reach our goals is through extensive testing sessions
and a zest to challenge yourself on a routine. Start
with the basics and use software calculation tools and
reduce your chemical needs where you can.
Last thought - Please note that these are my
observations not a critical lab experience. Its very
important to look at all options and in particular
listen to people like Ron, Vince, Eduoard, Ivor and
those who produce software for calculations because
they have lots of knowledge and understanding what
makes all this tick. My goals are simple, I am a
visual artist and I look for ways to increase visual
appeal while reducing any dangers I can in the studio
and in the products I make and I try to keep an open
mind. If something really clicks with me I have it
worked over in a lab and I check every angle possible
to make sure its repeatable. Luckily I had some good
teachers in the past and a couple that made me mad
enough to challenge myself to find my own answers. I
will try and get some kind of web page up on some of
this as soon as I can so you can see a few pictures of
all this craziness going on. I need 10 kilns and 20
people to keep up with all the things I want to do in
the next 2 months.
William Edwards
=====
http://www.tallapoosariverpottery.com/
Bill Edwards
PO Box 267
Lafayette, AL, 36862
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