Is it microwavable?

Hi Everyone,
Often I use a speckled clay (Standard 112) which I fire to cone 6.
Recently another potter said it was not microwavable due to the
manganese content which makes the speckles. I was wondering if anyone
else knows this to be true.
Thank you for your help,
Sandi

That is a new one for me. I use that clay and have no problem sticking it
in the microwave. You can actually use metal in the microwave as long as
you have enough mass of liquid (so you can have a themometer, spoon, etc. in
the dish if it has enough food in it. If however, you see arcing or sparks,
turn things off and don't do whatever it was you were doing.

Donna

"Red Deer" wrote in message
oups.com...
Hi Everyone,
Often I use a speckled clay (Standard 112) which I fire to cone 6.
Recently another potter said it was not microwavable due to the
manganese content which makes the speckles. I was wondering if anyone
else knows this to be true.
Thank you for your help,
Sandi

DKat wrote:
That is a new one for me. I use that clay and have no problem sticking it
in the microwave. You can actually use metal in the microwave as long as
you have enough mass of liquid (so you can have a themometer, spoon, etc. in
the dish if it has enough food in it. If however, you see arcing or sparks,
turn things off and don't do whatever it was you were doing.

Donna

"Red Deer" wrote in message
oups.com...
Hi Everyone,
Often I use a speckled clay (Standard 112) which I fire to cone 6.
Recently another potter said it was not microwavable due to the
manganese content which makes the speckles. I was wondering if anyone
else knows this to be true.
Thank you for your help,
Sandi

Thank you, Donna. I've used it too in the microwave with no problem. The other potter told me that you can't see the arcing but that she had to replace some expensive part in her oven because of that. I'm thinking that she may just think it was because of that type of clay. Who knows, the part may have been getting ready to go bad anyway and not from the clay.
Sandi

"Red Deer" wrote in message
ups.com...

DKat wrote:
That is a new one for me. I use that clay and have no problem sticking
it
in the microwave. You can actually use metal in the microwave as long as
you have enough mass of liquid (so you can have a themometer, spoon, etc.
in
the dish if it has enough food in it. If however, you see arcing or
sparks,
turn things off and don't do whatever it was you were doing.

Donna

"Red Deer" wrote in message
oups.com...
Hi Everyone,
Often I use a speckled clay (Standard 112) which I fire to cone 6.
Recently another potter said it was not microwavable due to the
manganese content which makes the speckles. I was wondering if anyone
else knows this to be true.
Thank you for your help,
Sandi

Thank you, Donna. I've used it too in the microwave with no problem.
The other potter told me that you can't see the arcing but that she had
to replace some expensive part in her oven because of that. I'm
thinking that she may just think it was because of that type of clay.
Who knows, the part may have been getting ready to go bad anyway and not
from the clay.
Sandi


I really doubt that this problem came from the pottery. For one thing, if
there is sufficient metal in the piece you are gong to notice it when you
touch the pot. It will be far hotter than the food it contains. Second,
way too many people use 112 for it not to have been noticed by others. A
quick check comes up with nothing on this but I will ask around.

Donna

P.S. Does this mean they also don't use high iron glazes in the microwave?

i don't know how current it is today, but years ago the word was to put
a piece in the micro for 30 seconds on hi. empty. if it came out
basically the same temp as it went it, it's fine. if it comes out
distinctly hot, it's not micro safe.

see ya

steve



On Nov 26, 3:36*pm, "DKat" wrote:
"Red Deer" wrote in oglegroups.com...







DKat wrote:
That is a new one for me. *I use that clay and have no problem sticking
it
in the microwave. *You can actually use metal in the microwave as long as
you have enough mass of liquid (so you can have a themometer, spoon, etc.
in
the dish if it has enough food in it. *If however, you see arcing or
sparks,
turn things off and don't do whatever it was you were doing.

Donna

"Red Deer" wrote in message
groups.com...
Hi Everyone,
Often I use a speckled clay (Standard 112) which I fire to cone 6.
Recently another potter said it was not microwavable due to the
manganese content which makes the speckles. I was wondering if anyone
else knows this to be true.
Thank you for your help,
Sandi

Thank you, Donna. *I've used it too in the microwave with no problem.
The other potter told me that you can't see the arcing but that she had
to replace some expensive part in her oven because of that. *I'm
thinking that she may just think it was because of that type of clay.
Who knows, the part may have been getting ready to go bad anyway and not
from the clay.
SandiI really doubt that this problem came from the pottery. *For one thing, if
there is sufficient metal in the piece you are gong to notice it when you
touch the pot. *It will be far hotter than the food it contains. *Second,
way too many people use 112 for it not to have been noticed by others. *A
quick check comes up with nothing on this but I will ask around.

Donna

P.S. *Does this mean they also don't use high iron glazes in the microwave?- Hide quoted text -- Show quoted text -

On 26 Nov 2006 20:13:14 -0800, "steve "
wrote:

i don't know how current it is today, but years ago the word was to put
a piece in the micro for 30 seconds on hi. empty. if it came out
basically the same temp as it went it, it's fine. if it comes out
distinctly hot, it's not micro safe.


The way I prefer to test is to have a second container holding
water, next to your dry piece under test. Then run the micro
on high until the water boils, and see if the test piece is warm.
This avoids the possible danger to the microwave of running
it without something to heat, which is a problem for some units
(or was... maybe new ones no longer have this problem).

As for the high-iron glazes, I have been unable to verify for myself
that they can get hot in the micro. This was a topic on Clayart
earlier in the year, and my initial feeling at the time was that this
was unlikely, since the iron would be embedded in an insulating
glassy matrix and would not be conductive. More likely is
that a piece that isn't fully vitrified will absorb some water (which
is a good microwave "susceptor") and that would heat up.
(I have seen this happen. The proof is that you can cook the
piece in a conventional oven for a couple of hours on low heat
to slowly drive out the water, after which the microwave heating
no longer happens... until the piece is run through the dishwasher
again, etc.)

However, as a result of the Clayart exchange, one potter reported
a high-iron glaze that reliably caused microwave heating. After
close questioning and several control tests on her part, I am more
inclined to believe it is a real phenomenon. Alas, I have not been
able to duplicate her result. The glaze was Bailey's Red cone 10.
I have tried the cone 6 version with no luck, but that may be due
to my tiny fast-cooling kiln... I also don't get a decent red. I
think the red is caused by iron crystals forming in the slow-cooling
glaze, and I suspect that maybe they can get big enough to heat up
individually, even if they are insulated from each other by the
glassy matrix so they don't form a large conductor. But that's
only a working hypothesis until I get a larger kiln (or a better
controller than me manually trying to do a forced cool-down.)

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

"Bob Masta" wrote in message
...
On 26 Nov 2006 20:13:14 -0800, "steve "
wrote:

i don't know how current it is today, but years ago the word was to put
a piece in the micro for 30 seconds on hi. empty. if it came out
basically the same temp as it went it, it's fine. if it comes out
distinctly hot, it's not micro safe.


The way I prefer to test is to have a second container holding
water, next to your dry piece under test. Then run the micro
on high until the water boils, and see if the test piece is warm.
This avoids the possible danger to the microwave of running
it without something to heat, which is a problem for some units
(or was... maybe new ones no longer have this problem).

As for the high-iron glazes, I have been unable to verify for myself
that they can get hot in the micro. This was a topic on Clayart
earlier in the year, and my initial feeling at the time was that this
was unlikely, since the iron would be embedded in an insulating
glassy matrix and would not be conductive. More likely is
that a piece that isn't fully vitrified will absorb some water (which
is a good microwave "susceptor") and that would heat up.
(I have seen this happen. The proof is that you can cook the
piece in a conventional oven for a couple of hours on low heat
to slowly drive out the water, after which the microwave heating
no longer happens... until the piece is run through the dishwasher
again, etc.)

However, as a result of the Clayart exchange, one potter reported
a high-iron glaze that reliably caused microwave heating. After
close questioning and several control tests on her part, I am more
inclined to believe it is a real phenomenon. Alas, I have not been
able to duplicate her result. The glaze was Bailey's Red cone 10.
I have tried the cone 6 version with no luck, but that may be due
to my tiny fast-cooling kiln... I also don't get a decent red. I
think the red is caused by iron crystals forming in the slow-cooling
glaze, and I suspect that maybe they can get big enough to heat up
individually, even if they are insulated from each other by the
glassy matrix so they don't form a large conductor. But that's
only a working hypothesis until I get a larger kiln (or a better
controller than me manually trying to do a forced cool-down.)

Best regards,




Bob Masta
dqatechATdaqartaDOTcom


I was actually asking about the RIO glaze with tongue in cheek... Need an
emo for that. I have a great many things with Randy's Red which has 15% RIO
and have never had a problem with them heating up. I do think that you need
some fluid in the piece when sticking it in the microwave. It is really
clear when you have a pot that doesn't belong in there. I had a slip cast
mugs from a give away and I have no idea what was in the glaze but I can
tell you I never drank out of it after the first time I microwaved it and
the cup became way noticeably hotter than what it contained. My first
thought was "LEAD!". Probably not but I didn't want to play the game of
waiting until my hair started falling out.

Donna

On Mon, 27 Nov 2006 17:14:10 -0500, "DKat"
wrote:

I was actually asking about the RIO glaze with tongue in cheek... Need an
emo for that. I have a great many things with Randy's Red which has 15% RIO
and have never had a problem with them heating up. I do think that you need
some fluid in the piece when sticking it in the microwave. It is really
clear when you have a pot that doesn't belong in there. I had a slip cast
mugs from a give away and I have no idea what was in the glaze but I can
tell you I never drank out of it after the first time I microwaved it and
the cup became way noticeably hotter than what it contained. My first
thought was "LEAD!". Probably not but I didn't want to play the game of
waiting until my hair started falling out.

Donna


Those slip-cast mug symptoms sound like the
ones I experienced, also in a slip-cast mug.
The rim in particular would get really hot.
But that was just due to trapped moisture
in the unvitrified body... drying it out in a 250F
oven for a couple of hours ended the problem,
at least temporarily. I suspect that even if the
mug never gets wet, it will pick up moisture
from the air through the porous footring.

I don't think lead can be the problem, because
I don't think it can be conductive in a glaze.
In order for something to be heated in a microwave,
it has to be either:

1) A polar molecule like water with slightly positive and
negative ends that the microwaves can grab onto,
AND it must be free to be dragged around. (Not
bound into a matrix.) This can happen in ceramic
glazes, but only at high temperatures where the
polar molecules can move a bit/

or

2) A (partial) conductor such as metal or silicon carbide.
In this case the microwaves cause heating by inducing
circulating currents in the conductor, and the current
passing through the resistance of the conductor is
what generates the heat, just like in any electric heater.
Nothing has to move for this to happen (well, other than
conduction electrons), but you need a continuous
conductor of some size. I don't know if you had tiny
conductive particles, just how small they can be and
still heat up. But the heating efficiency would go way
down if the size got too much smaller than the size
of the microwaves, and despite their name they are
not "micro" anything... more like a centimeter. So I'd
expect you'd need at least millimeter-sized crystals to
get any noticeable heating, as a first guess. Not
something I'd expect in a lead glaze.

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

"Bob Masta" wrote in message
...


Those slip-cast mug symptoms sound like the
ones I experienced, also in a slip-cast mug.
The rim in particular would get really hot.
But that was just due to trapped moisture
in the unvitrified body... drying it out in a 250F
oven for a couple of hours ended the problem,
at least temporarily. I suspect that even if the
mug never gets wet, it will pick up moisture
from the air through the porous footring.

I don't think lead can be the problem, because
I don't think it can be conductive in a glaze.
In order for something to be heated in a microwave,
it has to be either:

1) A polar molecule like water with slightly positive and
negative ends that the microwaves can grab onto,
AND it must be free to be dragged around. (Not
bound into a matrix.) This can happen in ceramic
glazes, but only at high temperatures where the
polar molecules can move a bit/

or

2) A (partial) conductor such as metal or silicon carbide.
In this case the microwaves cause heating by inducing
circulating currents in the conductor, and the current
passing through the resistance of the conductor is
what generates the heat, just like in any electric heater.
Nothing has to move for this to happen (well, other than
conduction electrons), but you need a continuous
conductor of some size. I don't know if you had tiny
conductive particles, just how small they can be and
still heat up. But the heating efficiency would go way
down if the size got too much smaller than the size
of the microwaves, and despite their name they are
not "micro" anything... more like a centimeter. So I'd
expect you'd need at least millimeter-sized crystals to
get any noticeable heating, as a first guess. Not
something I'd expect in a lead glaze.

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

Fun to know. Note I didn't say good to know because there goes my made up
check for lead in glaze..... I really hate giving up my unreality based
miniworlds...

Donna