Michael Wendt on sun 11 dec 11
Gina,
In answer to this part, as elements get older, they increase
in
resistance. The rule with Ohm's Law is:
P=3DI^2*R where P=3Dpower in Watts, I is current in Amps
and
R is resistance in Ohms
so it would look like at first glance that as resistance
went up, so would
the power developed, but...
the rest of the story is:
I=3D E/R where I is current in Amps =3D E is Voltage/ R is
Resistance
let the new resistance be 12 Ohms and the voltage be 120
volts
120/12=3D 10 amps I^2*R yields 10 x 10 x 12 =3D 1200
watts
now the old elements have 13.3 ohms resistance
so 120/13.3=3D 9 amps here I^2*R yields 9 x 9 x 13.3 =3D
1077 watts
that's the rub... as the elements increase in resistance
their power output
declines due to P=3DI^2*R
Aren't you glad you asked?
Regards,
Michael Wendt
My co worker said the
elements are getting old and so it fires hotter. Is this
true? I find it hard to believe.
Months ago the kiln was still firing hot and the pink didn't
burn out. could the glaze be contaminated?
It's hard to look at a group of crying kids when you don't
have a clue what happened.
Thank you and Happy Holidays to all!
Gina Mars
www.marspottery.net
New York=3D
gina mars on sun 11 dec 11
Hi All, As classes come to an end for the year, I've encountered a =3D
problem with some glazes.
We have a butterscotch cone 6 glaze that seems to literally peel off =3D
your piece after you dip it.
I encourage students to sponge their work before they dip it . I dipped =3D
a piece myself once in the
butterscotch alone and another piece I dipped in a citrus glaze, let it =3D
dry and then I dipped the rim in
the butterscotch. Within 5 minutes, it completely peeled off. I've =3D
noticed this with a few other glazes too.
At home i have a cone 10 flambe recipe i put over red and it does the =3D
same peeling. Now I
spray it but we do not have that option at our school.Some time ago I =3D
heard glazes with lots of clay content
do this but I do not think these recipes which have been around have =3D
lots of clay in them.
Any suggestions?
Also, we use Red, purple, pink mauve which is supposed to come out pink =3D
and is now
coming out grey. Children put it on coil pots , adults on platters and =3D
all grey. A cone pack was put
in the electric kiln and 8 was down all the way for a cone 6 firing. My =3D
co worker said the
elements are getting old and so it fires hotter. Is this true? I find it =
=3D
hard to believe.
Months ago the kiln was still firing hot and the pink didn't burn out. =3D
could the glaze be contaminated?
It's hard to look at a group of crying kids when you don't have a clue =3D
what happened.
Thank you and Happy Holidays to all!
Gina Mars
www.marspottery.net
New York=3D
Michael Wendt on sun 11 dec 11
Gina,
Commercial glazes often contain binders that make them able
to
take recoating after they dry. Some of my glazes I make will
allow
recoating but I found the best way to assure layers don't
peel
is to let them dry, bisque fire them and then layer on the
next layer.
Even though this seems like a lot of trouble, one failed pot
costs
more than the electricity and time it takes to refire.
As to color loss... overfiring a glaze intended for cone 6
to cone 8
(I am guessing you mean cone 6 not cone 06 and cone 8 not
cone 08?)
can sometimes bleach out the color. If you are using a
computer'
controlled kiln, I can assure you that witness cones are the
only
way to fire some glazes, especially those that are prone to
lose
color if fired too hot or not hot enough and especially
those that
run and stick pieces to the kiln shelf.
Regards,
Michael Wendt
Gina wrote:
Hi All, As classes come to an end for the year, I've
encountered a problem with some glazes.
We have a butterscotch cone 6 glaze that seems to literally
peel off your piece after you dip it.
I encourage students to sponge their work before they dip it
. I dipped a piece myself once in the
butterscotch alone and another piece I dipped in a citrus
glaze, let it dry and then I dipped the rim in
the butterscotch. Within 5 minutes, it completely peeled
off. I've noticed this with a few other glazes too.
At home i have a cone 10 flambe recipe i put over red and it
does the same peeling. Now I
spray it but we do not have that option at our school.Some
time ago I heard glazes with lots of clay content
do this but I do not think these recipes which have been
around have lots of clay in them.
Any suggestions?
Also, we use Red, purple, pink mauve which is supposed to
come out pink and is now
coming out grey. Children put it on coil pots , adults on
platters and all grey. A cone pack was put
in the electric kiln and 8 was down all the way for a cone 6
firing. My co worker said the
elements are getting old and so it fires hotter. Is this
true? I find it hard to believe.
Months ago the kiln was still firing hot and the pink didn't
burn out. could the glaze be contaminated?
It's hard to look at a group of crying kids when you don't
have a clue what happened.
Thank you and Happy Holidays to all!
Gina Mars
www.marspottery.net
New York=3D
Url Krueger on sun 11 dec 11
On 12/11/2011 05:36 AM, gina mars wrote:
> in the electric kiln and 8 was down all the way for a cone 6 firing.
Gina,
I would be suspicious that your thermocouple(s) may be
aging and giving you too low a reading resulting in the
kiln firing too long/hot. I had this happen to me and a
new thermocouple put my kiln right back on track.
earl
usa
oregon
hillsboro
Snail Scott on sun 11 dec 11
On Dec 11, 2011, at 7:36 AM, gina mars wrote:
> We have a butterscotch cone 6 glaze that seems to literally peel off =3D
your piece after you dip it...
Some glazes, especially those with a lot of clay,=3D20
have a high wet-to-dry shrinkage, and if thick=3D20
can peel right off the clay. If applied over a less=3D20
fussy glaze, they can even make that other glaze=3D20
peel off with it. Suggestions: apply the glaze to=3D20
slightly wet bisque, and if applying over another=3D20
glaze, make sure that first glaze has a bit of=3D20
residual moisture still in it. It may be that this glaze=3D20
will work best on greenware. If you don't care to=3D20
do this, consider reformulating with less clay.
> Also, we use Red, purple, pink mauve which is supposed to come out =3D
pink and is now
> coming out grey. Children put it on coil pots , adults on platters =3D
and all grey...
These colors are notoriously fussy. First:=3D20
make sure they are applied thickly. Second:=3D20
make sure they are applied to well-bisqued=3D20
ware, with no single-fire stuff in the load with=3D20
them. Third: better to slightly underfire rather=3D20
than risk overfiring.
> A cone pack was put
> in the electric kiln and 8 was down all the way for a cone 6 firing. =3D
My co worker said the
> elements are getting old and so it fires hotter. Is this true? I find =3D
it hard to believe...
Are you using a computer controller? Have you=3D20
calibrated the pyrometer readings based on the=3D20
witness cones? The digital readout can often be=3D20
wildly wrong. Doesn't mean you have to scrap it,=3D20
or even repair it, but you do need to program in=3D20
the correct offset otherwise. In any case, don't=3D20
just live with it, do something about it.
-Snail
Lis Allison on mon 12 dec 11
On December 11, 2011, gina mars wrote:
>...
> Also, we use Red, purple, pink mauve which is supposed to come out pink
> and is now coming out grey.
Are you using a different glaze? The reds, pinks, mauves and purples are
all touchy. They need to be on thick enough (but not so thick they become
dry and crusty) and they need to be on or under a glaze that does not
'kill' those colours. Any boron, or too much zinc in a glaze and you can't
get the reds. They either go grey or disappear entirely. Sometimes you get
a tiny bit of bright purply-red and that is a clue that there was boron in
the glaze.
Gerstley borate is the usual culprit.
Lis
--
Elisabeth Allison
Pine Ridge Studio
website: www.pine-ridge.ca
Pottery blog: www.studio-on-the-ridge.blogspot.com
Garden blog: www.garden-on-the-ridge.blogspot.com
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