Barbara Mueller on fri 27 sep 02
The kiln goddess was good to me yesterday. I opened my kiln (Electric
fired to Cone 6) and all the pieces were in one piece and I even liked
some of them. Would like to share some observations and asked some
questions.
I am using a clay body which is high in iron (Laguna Speckled Buff).
Last glaze firing I had some issues with the slip that I used leaving
some lumps, Vince, et al. recommended that I sieve which I did and it
took care of the problems. Slips made with the same clay body with
colorant work great! Thanks. Some interesting findings though.
There were about (five) 10 inch plates with large rims and on two of
them, which were fine in the bisque firings, the rims flattened out in
the glaze firing. Seemed strange to me. First thing I did was got out
my trusty calipers. The thicknesses of the rims in inches were, .160,
.260, .280, .300, and .310. The .160 which had slip brushed on the rim
flattened, the .260 which had light slip was fine, the .280 which had
heavily slip flattened, the .300 with slip was fine, and the .310 was
fine. I would look at that and say, rims need to be at least .260 with
out slip and more then .280 with heavy slip not to get the flattening
effect. I wonder though do rims just generally need to be thicker then I
am making them? Does slip have anything to do with it? Look for others
experiences because I am confused by this.
Secondly I had created a glaze accidentally and loved it. Lily
challenged me to get back in the kitchen and figure it out, so I did.
Did a line blend first to see what the effects of Titanium vs. Rutile
were in glaze. Took the High Calcium Semimatte Base #2 glaze from the
Mastering Cone 6 glaze book and varied the amount of Rutile vs. Titanium
with no colorant added and the color variation was significant. Clay
body had a lot of iron and it went from a creamy sort of color (100%
Rutile) to a putty sort of color (100% Titanium) Liked a mix of about
75% Rutile and 25% Titanium. When adding colorant to it, 3% copper
carbonate and 1.5% cobalt carbonate, it ran the range of green (100%
Titanium) to blue (100% Rutile). Not sure what that means and will
continue to think about it.
Thirdly, I had the experience of doing the same glaze, sprayed the same
way, on the same clay body and it looking very different when it came
out of the kiln. The glaze on the bottom of the kiln looked green and
the glaze on the top shelf looked blue. Comments?
Okay there is one more thing. I used some stains on my rims during
glazing to give some of them definition. I know this is eye thing but
does some one have a proportion to start with. Mine seemed weaker then
I had thought they would be and I used lots. To get a darker color
would it be better to not just mixing it with water?
Thanks
Barb
Who is going to talk to 200 elementary school children today about being
an inventor and hoping that I can inspire them to walk where no one has
walked before and open their personal tool box and fill it with
fascination, observation, inspiration and innovation.
Dave Finkelnburg on fri 27 sep 02
Barb,
It's really not the slip, I think.
Have you done any absorption test? Fire an unglazed tile and weigh it
on a very accurate (to 1/10th gram is best) scale while still warm from the
kiln, then soak at least 24 hours in water or boil 2 or 3 hours, put in cool
water, then pat dry and weigh quickly. Calculate the weight gain as a % of
the starting weight. You should have over 1% absorption, more like 1.5 to
2.5% for stoneware. For porcelain, 1/2% is common, though.
Anyway, I expect you will find your numbers are on the low side,
indicating you are near overfiring the clay, which weakens it enough to do
what it's doing. I routinely make stoneware thinner. Of course, if the
rims of your plate are totally flat, that shape is harder to support than if
they angle up a little.
Good potting,
Dave Finkelnburg in Idaho
----- Original Message -----
From: "Barbara Mueller"
To:
Sent: Friday, September 27, 2002 10:23 AM
Subject: Slips, Rutile vs. Titanium, Glaze variations
> The kiln goddess was good to me yesterday. I opened my kiln (Electric
> fired to Cone 6) and all the pieces were in one piece and I even liked
> some of them. Would like to share some observations and asked some
> questions.
>
>
>
> I am using a clay body which is high in iron (Laguna Speckled Buff).
> Last glaze firing I had some issues with the slip that I used leaving
> some lumps, Vince, et al. recommended that I sieve which I did and it
> took care of the problems. Slips made with the same clay body with
> colorant work great! Thanks. Some interesting findings though.
>
>
>
> There were about (five) 10 inch plates with large rims and on two of
> them, which were fine in the bisque firings, the rims flattened out in
> the glaze firing. Seemed strange to me. First thing I did was got out
> my trusty calipers. The thicknesses of the rims in inches were, .160,
> .260, .280, .300, and .310. The .160 which had slip brushed on the rim
> flattened, the .260 which had light slip was fine, the .280 which had
> heavily slip flattened, the .300 with slip was fine, and the .310 was
> fine. I would look at that and say, rims need to be at least .260 with
> out slip and more then .280 with heavy slip not to get the flattening
> effect. I wonder though do rims just generally need to be thicker then I
> am making them? Does slip have anything to do with it? Look for others
> experiences because I am confused by this.
>
>
>
> Secondly I had created a glaze accidentally and loved it. Lily
> challenged me to get back in the kitchen and figure it out, so I did.
> Did a line blend first to see what the effects of Titanium vs. Rutile
> were in glaze. Took the High Calcium Semimatte Base #2 glaze from the
> Mastering Cone 6 glaze book and varied the amount of Rutile vs. Titanium
> with no colorant added and the color variation was significant. Clay
> body had a lot of iron and it went from a creamy sort of color (100%
> Rutile) to a putty sort of color (100% Titanium) Liked a mix of about
> 75% Rutile and 25% Titanium. When adding colorant to it, 3% copper
> carbonate and 1.5% cobalt carbonate, it ran the range of green (100%
> Titanium) to blue (100% Rutile). Not sure what that means and will
> continue to think about it.
>
>
>
> Thirdly, I had the experience of doing the same glaze, sprayed the same
> way, on the same clay body and it looking very different when it came
> out of the kiln. The glaze on the bottom of the kiln looked green and
> the glaze on the top shelf looked blue. Comments?
>
>
>
> Okay there is one more thing. I used some stains on my rims during
> glazing to give some of them definition. I know this is eye thing but
> does some one have a proportion to start with. Mine seemed weaker then
> I had thought they would be and I used lots. To get a darker color
> would it be better to not just mixing it with water?
>
>
>
> Thanks
>
> Barb
>
>
>
> Who is going to talk to 200 elementary school children today about being
> an inventor and hoping that I can inspire them to walk where no one has
> walked before and open their personal tool box and fill it with
> fascination, observation, inspiration and innovation.
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Barbara Mueller on sat 28 sep 02
David I think I agree with you its not the slip. I am not sure that I
can describe this with out a picture but I will try. I put all of the
pieces upside down on a table and looked closely at the ones that fell.
I think its structural. I was trying to duplicate the shape both top
and bottom which I read is the goal. The plates where the shape of the
rim which is wide had a little more diagional support underneath meaning
the rim was not quite as wide underneath (maybe only by 3/8 of an inch)
didn't fall. Also think that I made them totally flat because I read
that they will have a tendency to warp upwards which made sense to me
with shrinkage. I will do the tile test though. Thanks for that tip.
Thought I would be able to come and see you David before we headed back
east for the winter. Will have to wait until we return to Coeur d'
Alene in the spring. Hope the rains come soon
Barb
Who spoke to the elementary school children about being inventors and
did not once mention that she had lucky underwear that she wore when she
was in design mode.
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Dave Finkelnburg
Sent: Friday, September 27, 2002 11:45 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Slips, Rutile vs. Titanium, Glaze variations
Barb,
It's really not the slip, I think.
Have you done any absorption test? Fire an unglazed tile and weigh
it
on a very accurate (to 1/10th gram is best) scale while still warm from
the
kiln, then soak at least 24 hours in water or boil 2 or 3 hours, put in
cool
water, then pat dry and weigh quickly. Calculate the weight gain as a %
of
the starting weight. You should have over 1% absorption, more like 1.5
to
2.5% for stoneware. For porcelain, 1/2% is common, though.
Anyway, I expect you will find your numbers are on the low side,
indicating you are near overfiring the clay, which weakens it enough to
do
what it's doing. I routinely make stoneware thinner. Of course, if the
rims of your plate are totally flat, that shape is harder to support
than if
they angle up a little.
Good potting,
Dave Finkelnburg in Idaho
----- Original Message -----
From: "Barbara Mueller"
To:
Sent: Friday, September 27, 2002 10:23 AM
Subject: Slips, Rutile vs. Titanium, Glaze variations
> The kiln goddess was good to me yesterday. I opened my kiln (Electric
> fired to Cone 6) and all the pieces were in one piece and I even liked
> some of them. Would like to share some observations and asked some
> questions.
>
>
>
> I am using a clay body which is high in iron (Laguna Speckled Buff).
> Last glaze firing I had some issues with the slip that I used leaving
> some lumps, Vince, et al. recommended that I sieve which I did and it
> took care of the problems. Slips made with the same clay body with
> colorant work great! Thanks. Some interesting findings though.
>
>
>
> There were about (five) 10 inch plates with large rims and on two of
> them, which were fine in the bisque firings, the rims flattened out in
> the glaze firing. Seemed strange to me. First thing I did was got
out
> my trusty calipers. The thicknesses of the rims in inches were, .160,
> .260, .280, .300, and .310. The .160 which had slip brushed on the
rim
> flattened, the .260 which had light slip was fine, the .280 which had
> heavily slip flattened, the .300 with slip was fine, and the .310 was
> fine. I would look at that and say, rims need to be at least .260
with
> out slip and more then .280 with heavy slip not to get the flattening
> effect. I wonder though do rims just generally need to be thicker then
I
> am making them? Does slip have anything to do with it? Look for
others
> experiences because I am confused by this.
>
>
>
> Secondly I had created a glaze accidentally and loved it. Lily
> challenged me to get back in the kitchen and figure it out, so I did.
> Did a line blend first to see what the effects of Titanium vs. Rutile
> were in glaze. Took the High Calcium Semimatte Base #2 glaze from the
> Mastering Cone 6 glaze book and varied the amount of Rutile vs.
Titanium
> with no colorant added and the color variation was significant. Clay
> body had a lot of iron and it went from a creamy sort of color (100%
> Rutile) to a putty sort of color (100% Titanium) Liked a mix of about
> 75% Rutile and 25% Titanium. When adding colorant to it, 3% copper
> carbonate and 1.5% cobalt carbonate, it ran the range of green (100%
> Titanium) to blue (100% Rutile). Not sure what that means and will
> continue to think about it.
>
>
>
> Thirdly, I had the experience of doing the same glaze, sprayed the
same
> way, on the same clay body and it looking very different when it came
> out of the kiln. The glaze on the bottom of the kiln looked green and
> the glaze on the top shelf looked blue. Comments?
>
>
>
> Okay there is one more thing. I used some stains on my rims during
> glazing to give some of them definition. I know this is eye thing but
> does some one have a proportion to start with. Mine seemed weaker
then
> I had thought they would be and I used lots. To get a darker color
> would it be better to not just mixing it with water?
>
>
>
> Thanks
>
> Barb
>
>
>
> Who is going to talk to 200 elementary school children today about
being
> an inventor and hoping that I can inspire them to walk where no one
has
> walked before and open their personal tool box and fill it with
> fascination, observation, inspiration and innovation.
>
>
________________________________________________________________________
____
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
________________________________________________________________________
______
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
David Hendley on sat 28 sep 02
Barbara, I'll address a couple of your questions.
Falling rims:
This is mostly a function of your claybody; the more vitrified
and pyroplastic (becoming flexible at high heat) your body,
the more likely your rims will warp down during a glaze firing.
You just have to determine, by trial and error how much support
you need to leave for your clay in your firing.
Rutile vs. titanium:
Titanium dioxide is a refined product of mostly pure titanium
and LOI materials.
Rutile is a naturally occurring mineral that is predominately
titanium, but is contaminated with other oxides, mostly iron.
See my separate post concerning rutile for Richard Aerni's
more detailed explanation.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
who may be reached at melpots@pclink.com.
Pat Southwood on sat 28 sep 02
Dear Barbara,
Bizarrely, I have just observed the same phenomenon.
Keuper red clay , slip sponged on the1 and a 1/4" rim around a rectangular
press moulded dish. Glazed with a wash of copper oxide and a dip in
transparent, fired to 1120 ox. opposing sides of the dish flopped on the
long side, although in perfect symmetry. The only thing I was pushing was
the firing range of the transparent glaze. I usually DO fire it @ 1120 with
great success, but have never done it before with unsupported bits such as
flanges and wide edges. Usually this glaze would only go to 1060 ox.
Best wishes
Pat. Remembering to say where from...
Norfolk Broads, England.
----- Original Message -----
From: "Barbara Mueller"
To:
Sent: Friday, September 27, 2002 5:23 PM
Subject: Slips, Rutile vs. Titanium, Glaze variations
> The kiln goddess was good to me yesterday. I opened my kiln (Electric
> fired to Cone 6) and all the pieces were in one piece and I even liked
> some of them. Would like to share some observations and asked some
> questions.
>
>
>
> I am using a clay body which is high in iron (Laguna Speckled Buff).
> Last glaze firing I had some issues with the slip that I used leaving
> some lumps, Vince, et al. recommended that I sieve which I did and it
> took care of the problems. Slips made with the same clay body with
> colorant work great! Thanks. Some interesting findings though.
>
>
>
> There were about (five) 10 inch plates with large rims and on two of
> them, which were fine in the bisque firings, the rims flattened out in
> the glaze firing. Seemed strange to me. First thing I did was got out
> my trusty calipers. The thicknesses of the rims in inches were, .160,
> .260, .280, .300, and .310. The .160 which had slip brushed on the rim
> flattened, the .260 which had light slip was fine, the .280 which had
> heavily slip flattened, the .300 with slip was fine, and the .310 was
> fine. I would look at that and say, rims need to be at least .260 with
> out slip and more then .280 with heavy slip not to get the flattening
> effect. I wonder though do rims just generally need to be thicker then I
> am making them? Does slip have anything to do with it? Look for others
> experiences because I am confused by this.
>
>
>
> Secondly I had created a glaze accidentally and loved it. Lily
> challenged me to get back in the kitchen and figure it out, so I did.
> Did a line blend first to see what the effects of Titanium vs. Rutile
> were in glaze. Took the High Calcium Semimatte Base #2 glaze from the
> Mastering Cone 6 glaze book and varied the amount of Rutile vs. Titanium
> with no colorant added and the color variation was significant. Clay
> body had a lot of iron and it went from a creamy sort of color (100%
> Rutile) to a putty sort of color (100% Titanium) Liked a mix of about
> 75% Rutile and 25% Titanium. When adding colorant to it, 3% copper
> carbonate and 1.5% cobalt carbonate, it ran the range of green (100%
> Titanium) to blue (100% Rutile). Not sure what that means and will
> continue to think about it.
>
>
>
> Thirdly, I had the experience of doing the same glaze, sprayed the same
> way, on the same clay body and it looking very different when it came
> out of the kiln. The glaze on the bottom of the kiln looked green and
> the glaze on the top shelf looked blue. Comments?
>
>
>
> Okay there is one more thing. I used some stains on my rims during
> glazing to give some of them definition. I know this is eye thing but
> does some one have a proportion to start with. Mine seemed weaker then
> I had thought they would be and I used lots. To get a darker color
> would it be better to not just mixing it with water?
>
>
>
> Thanks
>
> Barb
>
>
>
> Who is going to talk to 200 elementary school children today about being
> an inventor and hoping that I can inspire them to walk where no one has
> walked before and open their personal tool box and fill it with
> fascination, observation, inspiration and innovation.
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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