clear glaze developes milky spots in place???

Hi all,

I'm having a hard time with a store bought clear glaze (cone 6). I bought
this glaze in powder form and mixed it myself. Since then I'm having
random problems with it, usually on big bowls with lots and lots of work
invested in them. Problem is: milky white translucent spots develop in
place where I guess the glaze is to thick, except we've been extremely
carefull about it not being to thick. What would cause a glaze to be so
extremely sensitive to thickness? Or is it a combination of the firing
conditions and this specific glaze? I spoke to a local potter about it and
he said he makes his own clear glaze and never sees this problem but has
seen it with store bought glazes before.

I posted some pics for anyone crazy (or nice!) enought to have a look I
would sincerely love any advice or comments...

www.dramaworks.ca/badpots/badpots.htm

Thanks,

Zander

Zander,

I see what you mean.

My immediate reaction is a tad under-fired

Are you firing with cones or just a controller?

Either way I suggest a 30 minute soak at the end, or if you can't do
that the next cone up.

I know it supposed to be cone 6, but, like the man said, this can be a
problem with off the shelf glazes. In the end you are far better off
making your own glazes if you can; you can adjust them to suit your kiln
and way of firing because you KNOW what's in 'em. With bought glazes the
ingredients are often a mystery and you are groping around in the dark!

Steve
Bath
UK


In article , Zander no@no.? writes
Hi all,

I'm having a hard time with a store bought clear glaze (cone 6). I bought
this glaze in powder form and mixed it myself. Since then I'm having
random problems with it, usually on big bowls with lots and lots of work
invested in them. Problem is: milky white translucent spots develop in
place where I guess the glaze is to thick, except we've been extremely
carefull about it not being to thick. What would cause a glaze to be so
extremely sensitive to thickness? Or is it a combination of the firing
conditions and this specific glaze? I spoke to a local potter about it and
he said he makes his own clear glaze and never sees this problem but has
seen it with store bought glazes before.

I posted some pics for anyone crazy (or nice!) enought to have a look I
would sincerely love any advice or comments...

www.dramaworks.ca/badpots/badpots.htm

Thanks,

Zander


--
Steve Mills
Bath
UK

Steve,

newbie question:
If I soak the kiln for 30 minutes will that move the cones beyond cone6
or will they stop moving at the peak temperature? I do normally soak the
kiln but only for 5 or 10 minutes until I see a cone6 at about 3 o'clock
or so.

I'm a new controller owner (bartlett v6-cf) so I'm still adjusting to
that but it's already a huge help in shelf to shelf consistency.

The shelf those clear pots were fired on showed a cone6 slightly
overfired (about 100degree on the orton scale, just past the top of the
plaque).

Do you think refiring those clear pots could help?

Thanks,

Zander

Steve Mills wrote in
:

Zander,

I see what you mean.

My immediate reaction is a tad under-fired

Are you firing with cones or just a controller?

Either way I suggest a 30 minute soak at the end, or if you can't do
that the next cone up.

I know it supposed to be cone 6, but, like the man said, this can be a
problem with off the shelf glazes. In the end you are far better off
making your own glazes if you can; you can adjust them to suit your
kiln and way of firing because you KNOW what's in 'em. With bought
glazes the ingredients are often a mystery and you are groping around
in the dark!

Steve
Bath
UK

"Zander" no@no wrote in message ...
Hi all,

I'm having a hard time with a store bought clear glaze (cone 6). I bought
this glaze in powder form and mixed it myself. Since then I'm having
random problems with it, usually on big bowls with lots and lots of work
invested in them. Problem is: milky white translucent spots develop in
place where I guess the glaze is to thick, except we've been extremely
carefull about it not being to thick. What would cause a glaze to be so
extremely sensitive to thickness? Or is it a combination of the firing
conditions and this specific glaze? I spoke to a local potter about it
and
he said he makes his own clear glaze and never sees this problem but has
seen it with store bought glazes before.

I posted some pics for anyone crazy (or nice!) enought to have a look I
would sincerely love any advice or comments...

www.dramaworks.ca/badpots/badpots.htm

Thanks,

Zander

Steves answer could be right, otherwise, haven't seen anything like it
myself. The commercial clear glaze I use can turn slightly milky over dark
clay if thick, but not nearly as noticably as this, and it is when it is
really thick. Firing to reach cone 6 in my electric kiln I set to 1200C and
soak for 30 minutes
For what its worth I don't think it ruins the pots at all, they look good.

"annemarie" wrote in
:

Steves answer could be right, otherwise, haven't seen anything like it
myself. The commercial clear glaze I use can turn slightly milky over
dark clay if thick, but not nearly as noticably as this, and it is
when it is really thick. Firing to reach cone 6 in my electric kiln I
set to 1200C and soak for 30 minutes
For what its worth I don't think it ruins the pots at all, they look
good.




Thanks Annemarie, I think maybe I'm not soaking long enough based on yours
and Steve's comments as well as tips read elsewhere. I fire with a
controller but base my program end temp on when a regular cone6 is just
touching the top of the plaque it's in. I have been holding for about 5-
10 minutes normally, I guess I'm worried if I up this to 30 min I'll just
be overfiring?

I'm confused about the effect of soaking on cones... I have to remember
that most of the ware is coming out fine. But this milky spot problem has
ruined about 10 large bowls in the last while, it's getting very
frustrating. I think I'm going to dump that glaze or save it for
experiments only.

Thanks,

Zander

OK,

Cones measure accumulated heatwork, controllers/pyrometers measure the
temperature prevailing at the exact moment you look at the readout, so
cones behave like clays and glazes. A long slow firing will achieve the
right amount of heatwork at a lower INDICATED temperature. It's exactly
the same as using a slow cooker.
You are doing absolutely the right thing checking your Controller
against the cone. So following on from above; yes the cone will soften
more. I fire my cones until the tip touches the kiln shelf it is stood
on.
By all means re-fire your work, and in the future glaze a little
thinner, and fire a little higher, or as I suggested a good soak.
I like to think of glaze firing as like putting on an overcoat; if you
rush out of the door putting the coat on as you do it takes about 25
yards or more to get it comfortable, and even then it not really right.
Better to put the coat on slowly and carefully and THEN walk out of the
door in a relaxed fashion.

:-)

Steve
Bath
UK


In article , Zander no@no.? writes
Steve,

newbie question:
If I soak the kiln for 30 minutes will that move the cones beyond cone6
or will they stop moving at the peak temperature? I do normally soak the
kiln but only for 5 or 10 minutes until I see a cone6 at about 3 o'clock
or so.

I'm a new controller owner (bartlett v6-cf) so I'm still adjusting to
that but it's already a huge help in shelf to shelf consistency.

The shelf those clear pots were fired on showed a cone6 slightly
overfired (about 100degree on the orton scale, just past the top of the
plaque).

Do you think refiring those clear pots could help?

Thanks,

Zander

Steve Mills wrote in
:

Zander,

I see what you mean.

My immediate reaction is a tad under-fired

Are you firing with cones or just a controller?

Either way I suggest a 30 minute soak at the end, or if you can't do
that the next cone up.

I know it supposed to be cone 6, but, like the man said, this can be a
problem with off the shelf glazes. In the end you are far better off
making your own glazes if you can; you can adjust them to suit your
kiln and way of firing because you KNOW what's in 'em. With bought
glazes the ingredients are often a mystery and you are groping around
in the dark!

Steve
Bath
UK



--
Steve Mills
Bath
UK

"Zander" wrote in message
. ..
"annemarie" wrote in
:

Steves answer could be right, otherwise, haven't seen anything like it
myself. The commercial clear glaze I use can turn slightly milky over
dark clay if thick, but not nearly as noticably as this, and it is
when it is really thick. Firing to reach cone 6 in my electric kiln I
set to 1200C and soak for 30 minutes
For what its worth I don't think it ruins the pots at all, they look
good.




Thanks Annemarie, I think maybe I'm not soaking long enough based on
yours
and Steve's comments as well as tips read elsewhere. I fire with a
controller but base my program end temp on when a regular cone6 is just
touching the top of the plaque it's in. I have been holding for about 5-
10 minutes normally, I guess I'm worried if I up this to 30 min I'll just
be overfiring?

I'm confused about the effect of soaking on cones... I have to remember
that most of the ware is coming out fine. But this milky spot problem has
ruined about 10 large bowls in the last while, it's getting very
frustrating. I think I'm going to dump that glaze or save it for
experiments only.

Thanks,

Zander

Just to add - the blistering is another issue that might be dealt with by
doing a soak at the right temperature.
Two sites that I recommend
http://ceramic-materials.com/cermat/...ble%20Shooting
http://www.masteringglazes.com/Pages/faqframe.html
And I think your pieces are quite lovely with or without the milky spots.
With the style I can see why you might want it not to happen but then there
are those who will like it because they do make each piece more unique...

Zander

Just to add - the blistering is another issue that might be dealt with
by doing a soak at the right temperature.
Two sites that I recommend
http://ceramic-materials.com/cermat/...ble%20Shooting
http://www.masteringglazes.com/Pages/faqframe.html
And I think your pieces are quite lovely with or without the milky
spots. With the style I can see why you might want it not to happen
but then there are those who will like it because they do make each
piece more unique...



Thanks Dkat,

I've already ordered the mastering... book! So I will wait for that to
come, We (my wife and I) are still very inexperienced with
glazes/firing etc.) so hopefully with all the great advice we've
received and a little more experience we will start having more success.


BTW, do you have any idea where to go to buy bulk sieve mesh? I want
to build my own but have struck out finding the mesh.

Thanks,

Zander

"Zander" wrote in message
. ..
Zander

Just to add - the blistering is another issue that might be dealt with
by doing a soak at the right temperature.
Two sites that I recommend
http://ceramic-materials.com/cermat/...ble%20Shooting
http://www.masteringglazes.com/Pages/faqframe.html
And I think your pieces are quite lovely with or without the milky
spots. With the style I can see why you might want it not to happen
but then there are those who will like it because they do make each
piece more unique...



Thanks Dkat,

I've already ordered the mastering... book! So I will wait for that to
come, We (my wife and I) are still very inexperienced with
glazes/firing etc.) so hopefully with all the great advice we've
received and a little more experience we will start having more success.


BTW, do you have any idea where to go to buy bulk sieve mesh? I want
to build my own but have struck out finding the mesh.

Thanks,

Zander

http://www.wovenwire.com/brass-strainer-cloth.htm
http://www.twpinc.com/twp/jsp/produc...d=384&page=buy
http://www.darbywire.com/wirecloth_stock.htm

Lots of places on the net but I have not bought any so could not recommend
anyone. I recently read a really cute way of making a strainer though -

Take a 5Gallon bucket and cut off a ring from the top of a few inches. Then
take the bottom that is left and drop it through the ring (think of the
wider part of each as being the top side). Where it catches mark the top
and bottom and cut off this second ring. Now put your screen on the inner
ring so that it is on the outside of the ring and covering the bottom (think
sock on a foot). Drop this screened ring into the outer ring and force it
down tight.

In article , W_D_Great_Divider
writes
http://www.wovenwire.com/brass-strainer-cloth.htm
http://www.twpinc.com/twp/jsp/produc...d=384&page=buy
http://www.darbywire.com/wirecloth_stock.htm

Lots of places on the net but I have not bought any so could not recommend
anyone. I recently read a really cute way of making a strainer though -

Take a 5Gallon bucket and cut off a ring from the top of a few inches. Then
take the bottom that is left and drop it through the ring (think of the
wider part of each as being the top side). Where it catches mark the top
and bottom and cut off this second ring. Now put your screen on the inner
ring so that it is on the outside of the ring and covering the bottom (think
sock on a foot). Drop this screened ring into the outer ring and force it
down tight.


OR:

get an off-cut of plastic drainpipe or a heavy duty plastic bucket with
its bottom cut off, heat up a hot-plate to about 300F put a piece of
cooking foil shiny side up on it, your mesh on that, and press the piece
of pipe or bucket onto that until you see it melting around the edges.
lift it off, put it on a cold surface for a few moments then peel off
the foil. Viola!

Steve
Bath
UK



--
Steve Mills
Bath
UK