Jason Russell on wed 5 apr 06
Hello John Hesselberth and Ron Roy,
I recently bought your book and I've been enjoying it very much. I just bought a used Cress kiln
with the Firemate system and I fired it to cone 6 for the first time with some test pieces in it. I
used the Glossy Base Glaze 2 and it didn't come out how I'd hoped. The glaze crawled and I don't
know why. First let me give you all the details. The glaze was poured into the inside of some
cups and I dipped some test tiles. The clay bodies were all from Georgies of Portland. They were
a red cone 6 stoneware, a dark brown/almost black cone 6 stoneware, and a cone 6 porcelain. I
didn't add any colorant to the glaze. Everything was bisqued to cone 04 and sponged off before
glazing. I was hoping for a clear glaze that produced a glossy surface that you could see the
claybody through. Instead it was milky. My only guess is that I applied the glaze too thick. Can
too thick of an application cause the crawling and milky color? I know you recommend using a
computer, but this kiln was almost brand new and it came with an envirovent for $800. I fired
with a 7 cone in the Kiln Sitter and used a 6 witness cone. The witness cone in 90% down, almost
touching the clay pad I set it in. On the porcelain the glaze completely fell off the inside walls of
the cup and settled in a thick pool at the bottom. On the colored clay bodies it separated in a few
areas but not like on the porcelain. I am planning on mixing up another batch and applying a
thinner coat. When I mixed the glaze I used the amount of water that the recipe called for, 90ml
for every 100g of dry. This next time I'll try my old college method of dipping my finger and
letting it roll off my nail. I would appreciate any suggestions or advice. Thanks.
Jason Russell
John Hesselberth on thu 6 apr 06
Hi Jason,
See some responses scattered below.
On Apr 5, 2006, at 4:40 PM, Jason Russell wrote:
> Hello John Hesselberth and Ron Roy,
> I recently bought your book and I've been enjoying it very much. I
> just bought a used Cress kiln
> with the Firemate system and I fired it to cone 6 for the first
> time with some test pieces in it. I
> used the Glossy Base Glaze 2 and it didn't come out how I'd hoped.
> The glaze crawled and I don't
> know why. First let me give you all the details. The glaze was
> poured into the inside of some
> cups and I dipped some test tiles. The clay bodies were all from
> Georgies of Portland. They were
> a red cone 6 stoneware, a dark brown/almost black cone 6 stoneware,
> and a cone 6 porcelain. I
> didn't add any colorant to the glaze. Everything was bisqued to
> cone 04 and sponged off before
> glazing. I was hoping for a clear glaze that produced a glossy
> surface that you could see the
> claybody through. Instead it was milky. My only guess is that I
> applied the glaze too thick. Can
> too thick of an application cause the crawling and milky color?
Well it certainly can cause a milky color. Very few, if any,
"transparent" glazes can be put on thick and still be transparent or
nearly so. All glazes have some residual tiny bubbles of gas or
undissolved impurities which will cause a small degree of opacity.
When they get thick that becomes noticeable. So for starters, thin
your glaze down a bit and do a test tile or two that has 1, 2, 3
dips on it so you can see the effect of glaze thickness.
Crawling can be caused by several things. First GB2 is the same base
as Licorice and some people have had trouble with Licorice crawling.
If the suggestions that follow don't solve your problem you might try
one of the revisions that are posted on our web site--mod 3 or 4
might work better for you. Go to
http://www.masteringglazes.com/Pages/faqframe.html
and look at Q3.
But there are other causes of crawling. You said you sponged off your
bisque before glazing. How wet was your sponge? If you got the bisque
fairly wet it would not have helped the crawling. Glazed pots should
always be dry before the stick the heat to them in glaze firing. I
always take that first 100 Deg F fairly slowly to make sure they are
dry before I turn the kiln up. Some people actually wash their bisque
first to get rid of dust and then let it dry for a day or two before
glazing. That has always puzzled me as I've never found it necessary.
At most I use a barely damp sponge and wipe them down, but mostly I
do nothing and rarely, if ever, have trouble with crawling (including
with Licorice--I have never been able to get it to crawl). Now if you
sand your greenware or bisque and stir up a lot of dust on the
surface perhaps it is needed.
> I know you recommend using a
> computer, but this kiln was almost brand new and it came with an
> envirovent for $800. I fired
> with a 7 cone in the Kiln Sitter and used a 6 witness cone. The
> witness cone in 90% down, almost
> touching the clay pad I set it in. On the porcelain the glaze
> completely fell off the inside walls of
> the cup and settled in a thick pool at the bottom.
GB2 is a pretty "thick" or stiff glaze and normally does not move
much at all. You may have a mixing error or an ingredient that is not
what it says it is on the bag. Or you may have a real hot spot in
your kiln where you had the porcelain cup. Place a cone right next to
your key test pieces in your next firing and be sure they are really
only seeing cone 6. While porcelain bodies will normally result in a
little more flow than the same glaze on a stoneware body I have never
seen GB2 or Licorice move much on porcelain. It could be that being
way too thick would also result in some movement.
> On the colored clay bodies it separated in a few
> areas but not like on the porcelain. I am planning on mixing up
> another batch and applying a
> thinner coat. When I mixed the glaze I used the amount of water
> that the recipe called for, 90ml
> for every 100g of dry.
That 90 ml/100 grams that we state in the book is only a starting
point. It usually assures that the glaze will not be too thin. I
almost always add a little more water to get the right consistency.
As we said in the book "This will vary quite a bit depending on the
specific ingredients you are using, but you can always add more
water..."
> This next time I'll try my old college method of dipping my finger and
> letting it roll off my nail. I would appreciate any suggestions or
> advice. Thanks.
> Jason Russell
Learning how to match glazes and kiln and clay bodies takes a while
with careful, patient observation. Since your kiln is new plan on
doing several test firings before you learn its characteristics well
enough to get the results your want. When you add new glazes to the
mix also you are potentially compounding the difficulty of getting
the system to behave the way you want it to. Good luck,
Regards,
John
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Ron Roy on sat 8 apr 06
Hi Jason,
If you had calculation software and calculated and compared Glossy base 1,
Glossy base 2, and glossy clear liner - you would see that Glossy base 2
would have the least chance of being clear because it has so much more
alumina and silica than the other two.
Perhaps you used the glossy base 2 because the other two had G200 and you
did not have any? In these types glazes you can usually sub Custer for G200
and visa versa without noticing any difference by the way.
I suggest you try two revisions of the Glossy base two - lowering the
alumina and silica - just do 500 gram batches to see if it helps with
making a clear glaze.
#1 lower the EPK by one and increase the whiting by one
#2 lower the EPK by two and increase the whiting by two.
Pay attention ti what John said - and how we recommend testing the glaze
for thickness before applying it,
Some glazes are prone to cracking and crawling - and sometimes it is due to
other factors such as water - one way that helps avoid crawling is to let
your glazed pots dry completely before firing - firing wet pots is a sure
way to make crawling happen if it's going to.
If you want to try the other two and want me to convert them to Custer for
you just let me know.
RR
>Hello John Hesselberth and Ron Roy,
>I recently bought your book and I've been enjoying it very much. I just
>bought a used Cress kiln
>with the Firemate system and I fired it to cone 6 for the first time with
>some test pieces in it. I
>used the Glossy Base Glaze 2 and it didn't come out how I'd hoped. The
>glaze crawled and I don't
>know why. First let me give you all the details. The glaze was poured
>into the inside of some
>cups and I dipped some test tiles. The clay bodies were all from Georgies
>of Portland. They were
>a red cone 6 stoneware, a dark brown/almost black cone 6 stoneware, and a
>cone 6 porcelain. I
>didn't add any colorant to the glaze. Everything was bisqued to cone 04
>and sponged off before
>glazing. I was hoping for a clear glaze that produced a glossy surface
>that you could see the
>claybody through. Instead it was milky. My only guess is that I applied
>the glaze too thick. Can
>too thick of an application cause the crawling and milky color? I know
>you recommend using a
>computer, but this kiln was almost brand new and it came with an
>envirovent for $800. I fired
>with a 7 cone in the Kiln Sitter and used a 6 witness cone. The witness
>cone in 90% down, almost
>touching the clay pad I set it in. On the porcelain the glaze completely
>fell off the inside walls of
>the cup and settled in a thick pool at the bottom. On the colored clay
>bodies it separated in a few
>areas but not like on the porcelain. I am planning on mixing up another
>batch and applying a
>thinner coat. When I mixed the glaze I used the amount of water that the
>recipe called for, 90ml
>for every 100g of dry. This next time I'll try my old college method of
>dipping my finger and
>letting it roll off my nail. I would appreciate any suggestions or
>advice. Thanks.
>Jason Russell
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Jason Russell on fri 14 apr 06
A quick thanks to everyone who responded to my original post. I'm glad it helped and sparked
some discussion. I'm still planning to test the base glaze #2 again, a little thinner this time, as
well as the liner glaze and maybe a few from the old Chappell book. It seems the tap water issue
is up for debate, but I'll try both tap water and water filtered through a Britta. Keep up the
discussions. Cheers!
Jason Russell
Portland, OR
Steve Slatin on fri 14 apr 06
Jason --
If you're really worried about water, I'd suggest
trying a small test with distilled water. Brita
filters remove some calcium, copper and lead but
aren't especially effective against sodium,
calcium, floride, and other materials.
(http://www.brita.com.au/help/frequently_asked_questions)
-- Steve Slatin
--- Jason Russell wrote:
> A quick thanks to everyone who responded to my
> original post. I'm glad it helped and sparked
> some discussion. I'm still planning to test
> the base glaze #2 again, a little thinner this
> time, as
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