heavy glaze questions, a small experimnet, unbalanced fluxes

updated mon 7 jun 04

Paul Raymond on thu 3 jun 04

To all, especially John and Ron,

Over the Memorial Day Weekend I had the opportunity to fire not once,
but twice. Both glaze kilns were filled with glazed bone-dry ware with
your Glaze Base 2 on the pots. As an experiment, and curious to follow
up on last weeks discussion surrounding matte glazes, as well as a
desire on my part to see what would happen by single firing some pots I
used 2 distinct firing schedules. For the first one, I went as I
normally do until I reached C6. At this point I increased the soak from
30 minutes to 1 hour then fired down to 2000 Degrees F. At that point I
ended the firing. The 2nd kiln was fired using my more typical schedule,
with a :30 min Soak at cone 6 (2232 degrees F) and then switching off.

I thought that you would be interested to know that the kiln that was
fired down was quite successful with a surprise. Your Glossy Base 2 with
5% add's of Iron, Tin, copper and rutile, resulted in a "mattening up"
of this glossy glaze. I referred to the glaze calc program and saw that
the Ca level for this was around 8.5 so my initial surprise was then
some what explained. The 2nd kiln with just the: 30 min soak resulted in
the very shiny glossy glaze surface that I am accustomed to with these
glazes.

As far as the single firing goes, a lot of crawling occurred, both with
my white body and the red. I will return to bisque firing. Some dunting
occurred as well. Most of this presented itself in the form of small,
volcanic fissures within an inch or so of the rim. One bowl has 2 cracks
equaling 2/3 of the circumference of the middle of the piece. However,
all pieces ring true and clear when rung with my finger.

It was a fun experiment. The biggest problem with all of this glaze
research and development is deciding which direction to go in as each
result reveals a new possibility. I am realizing that a clear sense of
ones' vision is important not just in getting pots out of the kiln but
in acquiring the type of dedication and focus required to achieve the
goals in mind.

Paul



Paul Raymond
Franklin, Tennessee
crazyrays@bellsouth.net

Carol Tripp on sat 5 jun 04

Part of what Paul wrote:
>I thought that you would be interested to know that the kiln that was
>fired down was quite successful with a surprise. Your Glossy Base 2 with
>5% add's of Iron, Tin, copper and rutile, resulted in a "mattening up"
>of this glossy glaze. I referred to the glaze calc program and saw that
>the Ca level for this was around 8.5 so my initial surprise was then
>some what explained. The 2nd kiln with just the: 30 min soak resulted in
>the very shiny glossy glaze surface that I am accustomed to with these
>glazes.
>


Hi Paul,
I am a bit curious about your CaO level being 8.5. I think you meant to
type .85 and if so, are you sure you are looking at the right recipe? It's
the High Calcium bases which have the CaO at .85. As an aside, you can make
these High Calcium glazes go glossy by putting them on too thick. Even a
slow fire-down will not make them matt up.
I have used the Glossy Base 2 for a clear glaze and it forms a haze of tiny
crystals during a slow fire-down. It's still glossy, but it is not clear.
However, it is not matt.

Best regards,
Carol
Dubai, UAE
Where it is so humid, it is foggy.

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Ron Roy on sat 5 jun 04

Hi Paul,

Cool just about anything slow enough and it will recrystalize - just a
matter of time.

With I had understood that in my fudge making days.

I'm curious - does anyone know how long a slow cool it would take to
recrystalize window glass?

RR


>I thought that you would be interested to know that the kiln that was
>fired down was quite successful with a surprise. Your Glossy Base 2 with
>5% add's of Iron, Tin, copper and rutile, resulted in a "mattening up"
>of this glossy glaze. I referred to the glaze calc program and saw that
>the Ca level for this was around 8.5 so my initial surprise was then
>some what explained. The 2nd kiln with just the: 30 min soak resulted in
>the very shiny glossy glaze surface that I am accustomed to with these
>glazes.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513

Ivor and Olive Lewis on sun 6 jun 04

Dear Ron Roy,
You ask <take to recrystallise window glass? >>
Charles Bray in "Dictionary of Glass. Materials and Techniques."
devotes half a page to this phenomenon of De-vitrification. Yes it
does happen. My old friend tells us that if the glass is held at its
liquidus temperature for longer than necessary and there is sufficient
Calcium in the Batch devitrification can happen. It can lead to all
sorts of defects, seeds, cords and crystals and cracking due to C of E
problems.
Because there is a rapid throughput of material from the tank to the
working process which causes rapid cooling it is not a frequent
occurrence. But, as I recall from my visits to Alloa and other
Scottish glass factories they did everything possible to avoid delays
due to breakdowns in bottle blowing plants.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
.

Paul Raymond on sun 6 jun 04

Hello Carol,

<to type .85 and if so, are you sure you are looking at the right
recipe?>>

I checked my numbers and I see that I misread the chart. The 8.5 came
from the weight column. The CaO in this glaze is .549 when measured with
the unity formula. You are also right to question me on the surface
quality of this glaze when fired down. It does remain glossy but your
description of a "haze of tiny crystals" is a more appropriate choice of
words. However, I think you will agree with me that in no way does this
glaze resemble itself when it is fired with out the long slow down. It
may have some shine to it but it very reduced. Not a true matte, yet not
a true gloss either, hence my use of the term "'mattening up' ".

Sincerely,

Paul

Paul Raymond
Franklin, Tennessee
crazyrays@bellsouth.net