Janet Coleman on mon 21 feb 00
Thanks to those who responded to my problem of the glaze drying slowly and
then cracking off the pot. I didn't include the recipie in the original
posting because I assumed that the problem was not related to recipie since
it was successfully used by the community studio (although I do purchase my
materials from a different supplier than they). But here is recipie -- it
is actually a 50/50 combination of two glazes, one of which I use alone and
the other which is used only in this combo:
gray: potash feldspar 20, gerstely borate 20, frit 3134 15, tenn. ball clay
15, and silica 30, plus cobalt carbonate 1.5, red iron oxide 1.5 and titanium
dioxide 5.
tan gloss: neph. syenite 38, silica 25, magnesium carbonate 3, zinc oxide 5,
gerstley borate 7, whiting 10, bone ash 4, bentonite 2, illmenite 2, rutile 2.
I don't think the problem is related to leaving the pot in the glaze too
long, as I do a pretty quick dipping and have been glazing pots for a number
of years and never had this specific problem. I also assume that it is not
because the glaze is too thick -- if anything the glaze looks a little too
thin to me and I was wondering if the problem might be due too it being too
watery -- or a combination of that and perhaps bisquing a little too high
(05). Also, I should mention that I'm using this glaze partially on top of
another glaze and the glaze has the most trouble where it sits on top of the
other glaze. I used this exact combination of glazes for at least a year
without any problem at the community studio.
Thanks for any further ideas
Janet
Paul Taylor on wed 23 feb 00
Dear Janet
These look like nice crystalline glazes.
But I would suspect they have very different shrinkage rates. The first
would raw glaze well. It has a good amount of clay in it, and would not
like too high a biscuit or to be too floculated - especially on the high
biscuit using a fine clay. The second is only held together by 2% bentonite
and would be less likely to shrink and more powdery.
If you put the second glaze on top of the first I can see no
problem. The other way round The glaze is likely to peel Having little grip
on the powdery surface. However if the first glaze was defloculated ( The
water it swims in a little alkaline) you would probably get away with it on
a soft biscuited pot.
If the glaze was left hanging about it would defloculate it's self ,
which may have come about in your shared workshop.
If you have moved from a hard water area to a soft one that would not
help but there I am speculating. ( Am I losing my sense of proportion) .
Regards Paul T
----------
>From: Janet Coleman
>To: CLAYART@LSV.UKY.EDU
>Subject: glaze drying slow and cracking- update
>Date: Mon, Feb 21, 2000, 9:28 pm
>
>----------------------------Original message----------------------------
>
>
>Thanks to those who responded to my problem of the glaze drying slowly and
>then cracking off the pot. I didn't include the recipie in the original
>posting because I assumed that the problem was not related to recipie since
>it was successfully used by the community studio (although I do purchase my
>materials from a different supplier than they). But here is recipie -- it
>is actually a 50/50 combination of two glazes, one of which I use alone and
>the other which is used only in this combo:
>
>gray: potash feldspar 20, gerstely borate 20, frit 3134 15, tenn. ball clay
>15, and silica 30, plus cobalt carbonate 1.5, red iron oxide 1.5 and titanium
>dioxide 5.
>
>tan gloss: neph. syenite 38, silica 25, magnesium carbonate 3, zinc oxide 5,
>gerstley borate 7, whiting 10, bone ash 4, bentonite 2, illmenite 2, rutile 2.
>
>I don't think the problem is related to leaving the pot in the glaze too
>long, as I do a pretty quick dipping and have been glazing pots for a number
>of years and never had this specific problem. I also assume that it is not
>because the glaze is too thick -- if anything the glaze looks a little too
>thin to me and I was wondering if the problem might be due too it being too
>watery -- or a combination of that and perhaps bisquing a little too high
>(05). Also, I should mention that I'm using this glaze partially on top of
>another glaze and the glaze has the most trouble where it sits on top of the
>other glaze. I used this exact combination of glazes for at least a year
>without any problem at the community studio.
>
>Thanks for any further ideas
>Janet
Cantello Studios on thu 24 feb 00
I not sure if this will help but I sometimes use 2 percent brown sugar
in my hi soda glazes to keep then from dusting out every time you pickup
the pot. I've been doing this for years and it works well. Also makes the
firing smell like backing cookies. Hope this helps Chris
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.UKY.EDU]On Behalf
Of Paul Taylor
Sent: Wednesday, February 23, 2000 9:32 AM
To: CLAYART@LSV.UKY.EDU
Subject: Re: glaze drying slow and cracking- update
----------------------------Original message----------------------------
Dear Janet
These look like nice crystalline glazes.
But I would suspect they have very different shrinkage rates. The first
would raw glaze well. It has a good amount of clay in it, and would not
like too high a biscuit or to be too floculated - especially on the high
biscuit using a fine clay. The second is only held together by 2% bentonite
and would be less likely to shrink and more powdery.
If you put the second glaze on top of the first I can see no
problem. The other way round The glaze is likely to peel Having little grip
on the powdery surface. However if the first glaze was defloculated ( The
water it swims in a little alkaline) you would probably get away with it on
a soft biscuited pot.
If the glaze was left hanging about it would defloculate it's self ,
which may have come about in your shared workshop.
If you have moved from a hard water area to a soft one that would not
help but there I am speculating. ( Am I losing my sense of proportion) .
Regards Paul T
----------
>From: Janet Coleman
>To: CLAYART@LSV.UKY.EDU
>Subject: glaze drying slow and cracking- update
>Date: Mon, Feb 21, 2000, 9:28 pm
>
>----------------------------Original message----------------------------
>
>
>Thanks to those who responded to my problem of the glaze drying slowly and
>then cracking off the pot. I didn't include the recipie in the original
>posting because I assumed that the problem was not related to recipie since
>it was successfully used by the community studio (although I do purchase my
>materials from a different supplier than they). But here is recipie -- it
>is actually a 50/50 combination of two glazes, one of which I use alone and
>the other which is used only in this combo:
>
>gray: potash feldspar 20, gerstely borate 20, frit 3134 15, tenn. ball clay
>15, and silica 30, plus cobalt carbonate 1.5, red iron oxide 1.5 and
titanium
>dioxide 5.
>
>tan gloss: neph. syenite 38, silica 25, magnesium carbonate 3, zinc oxide
5,
>gerstley borate 7, whiting 10, bone ash 4, bentonite 2, illmenite 2, rutile
2.
>
>I don't think the problem is related to leaving the pot in the glaze too
>long, as I do a pretty quick dipping and have been glazing pots for a
number
>of years and never had this specific problem. I also assume that it is not
>because the glaze is too thick -- if anything the glaze looks a little too
>thin to me and I was wondering if the problem might be due too it being too
>watery -- or a combination of that and perhaps bisquing a little too high
>(05). Also, I should mention that I'm using this glaze partially on top of
>another glaze and the glaze has the most trouble where it sits on top of
the
>other glaze. I used this exact combination of glazes for at least a year
>without any problem at the community studio.
>
>Thanks for any further ideas
>Janet
Ron Roy on sun 27 feb 00
There are some problems with the both glazes which can probably be fixed by
reformulating. Magnesium carb, Gerstley borate and Zinc oxide can all have
an adverse effect when it come to too much shrinkage of a raw glaze.
It is important with these kinds of glazes to let them dry completely
before trying to fire them - and to fire slowly during the beginning stages
of firing. Adding a binder - like sugar - as someone suggested will
sometimes work - it comes to the surface as the glaze dries and forms a
tough skin. It does go bad after a while and you need a strong stomach when
glazing.
If you want me to make suggestions about how to reformulate to avoid the
problem contact me off list.
RR
>>----------------------------Original message----------------------------
>>gray: potash feldspar 20, gerstely borate 20, frit 3134 15, tenn. ball clay
>>15, and silica 30, plus cobalt carbonate 1.5, red iron oxide 1.5 and
>titanium
>>dioxide 5.
>>
>>tan gloss: neph. syenite 38, silica 25, magnesium carbonate 3, zinc oxide
>5,
>>gerstley borate 7, whiting 10, bone ash 4, bentonite 2, illmenite 2, rutile
>2.
>>
>>I don't think the problem is related to leaving the pot in the glaze too
>>long, as I do a pretty quick dipping and have been glazing pots for a
>number
>>of years and never had this specific problem. I also assume that it is not
>>because the glaze is too thick -- if anything the glaze looks a little too
>>thin to me and I was wondering if the problem might be due too it being too
>>watery -- or a combination of that and perhaps bisquing a little too high
>>(05). Also, I should mention that I'm using this glaze partially on top of
>>another glaze and the glaze has the most trouble where it sits on top of
>the
>>other glaze. I used this exact combination of glazes for at least a year
>>without any problem at the community studio.
>>
>>Thanks for any further ideas
>>Janet
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Stephen Mills on tue 29 feb 00
Following on from the comment below; an old Majolica painters trick is
to dissolve 1 dessert spoon of sugar to one (UK) gallon of glaze. The
result when dry is a nice crisp surface to paint on that doesn't "pick
up" when touched by a loaded brush.
Steve
Bath
UK
In message , Cantello Studios writes
>----------------------------Original message----------------------------
>I not sure if this will help but I sometimes use 2 percent brown sugar
>in my hi soda glazes to keep then from dusting out every time you pickup
>the pot. I've been doing this for years and it works well. Also makes the
>firing smell like backing cookies. Hope this helps Chris
>
>-----Original Message-----
>From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.UKY.EDU]On Behalf
>Of Paul Taylor
>Sent: Wednesday, February 23, 2000 9:32 AM
>To: CLAYART@LSV.UKY.EDU
>Subject: Re: glaze drying slow and cracking- update
>
>
>----------------------------Original message----------------------------
>Dear Janet
> These look like nice crystalline glazes.
>
> But I would suspect they have very different shrinkage rates. The first
>would raw glaze well. It has a good amount of clay in it, and would not
>like too high a biscuit or to be too floculated - especially on the high
>biscuit using a fine clay. The second is only held together by 2% bentonite
>and would be less likely to shrink and more powdery.
>
> If you put the second glaze on top of the first I can see no
>problem. The other way round The glaze is likely to peel Having little grip
>on the powdery surface. However if the first glaze was defloculated ( The
>water it swims in a little alkaline) you would probably get away with it on
>a soft biscuited pot.
>
> If the glaze was left hanging about it would defloculate it's self ,
>which may have come about in your shared workshop.
>
> If you have moved from a hard water area to a soft one that would not
>help but there I am speculating. ( Am I losing my sense of proportion) .
>
> Regards Paul T
>
>
>
>----------
>>From: Janet Coleman
>>To: CLAYART@LSV.UKY.EDU
>>Subject: glaze drying slow and cracking- update
>>Date: Mon, Feb 21, 2000, 9:28 pm
>>
>
>>----------------------------Original message----------------------------
>>
>>
>>Thanks to those who responded to my problem of the glaze drying slowly and
>>then cracking off the pot. I didn't include the recipie in the original
>>posting because I assumed that the problem was not related to recipie since
>>it was successfully used by the community studio (although I do purchase my
>>materials from a different supplier than they). But here is recipie -- it
>>is actually a 50/50 combination of two glazes, one of which I use alone and
>>the other which is used only in this combo:
>>
>>gray: potash feldspar 20, gerstely borate 20, frit 3134 15, tenn. ball clay
>>15, and silica 30, plus cobalt carbonate 1.5, red iron oxide 1.5 and
>titanium
>>dioxide 5.
>>
>>tan gloss: neph. syenite 38, silica 25, magnesium carbonate 3, zinc oxide
>5,
>>gerstley borate 7, whiting 10, bone ash 4, bentonite 2, illmenite 2, rutile
>2.
>>
>>I don't think the problem is related to leaving the pot in the glaze too
>>long, as I do a pretty quick dipping and have been glazing pots for a
>number
>>of years and never had this specific problem. I also assume that it is not
>>because the glaze is too thick -- if anything the glaze looks a little too
>>thin to me and I was wondering if the problem might be due too it being too
>>watery -- or a combination of that and perhaps bisquing a little too high
>>(05). Also, I should mention that I'm using this glaze partially on top of
>>another glaze and the glaze has the most trouble where it sits on top of
>the
>>other glaze. I used this exact combination of glazes for at least a year
>>without any problem at the community studio.
>>
>>Thanks for any further ideas
>>Janet
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Tel: **44 (0)1225 311699
Fax: **44 (0)870 0526466
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