iandol on mon 12 jun 00
I have pondered before on these pages about the necessity for including =
Boric oxide in one form or another in glazes which mature upwards from =
cone 6. With the disappearance from suppliers shelves of Gerstly Borate =
I did wonder if people would abandon boron in this temperature range and =
rely totally on the group 1 and 2 fluxes.
I have always found the rhetoric of glaze maturing theory to be =
confusing. It seems incongruous to be told that materials used in glaze =
recipes, especially those containing Sodium, Potassium and to a lesser =
degree Calcium, melt because of low solidus temperatures -Eutectics- and =
then find that so much Boron substance has to be included to get a =
recipe to work.
Ivor Lewis.
Michael Banks on wed 14 jun 00
I don't think melting is the issue , Ivor. The Group I & II oxides promote
fusion just fine above (or below) cone 6, but the resulting glazes have too
high expansions to fit normal clay bodies. Boric oxide has extraordinary
low expansion, so using it as a flux and glass-former enables the high
expansion alkalis to be kept to lower levels.
Leave out boron if you don't mind a lot of crazing, otherwise you might just
have to resort to it. This is just one reason boron is useful in mid-fire
glazes. Others include it's ability to dissolve alumina while maintaining a
lower fluidity than silica/alkalis alone, lustre, unique colour response,
desirable textural (e.g. floating texture) and blush effects.
Michael Banks,
Nelson,
NZ
Ivor Lewis wrote:
----- Original Message -----
> I have pondered before on these pages about the necessity for including
Boric oxide in one form or another in
> glazes which mature upwards from cone 6. With the disappearance from
suppliers shelves of Gerstly Borate I did
> wonder if people would abandon boron in this temperature range and rely
totally on the group 1 and 2 fluxes.
> I have always found the rhetoric of glaze maturing theory to be confusing.
It seems incongruous to be told that
> materials used in glaze recipes, especially those containing Sodium,
Potassium and to a lesser degree Calcium,
> melt because of low solidus temperatures -Eutectics- and then find that so
much Boron substance has to be
> included to get a recipe to work.
Ron Roy on wed 14 jun 00
Hi Ivor,
Mostly potters use what seems to work - quick answers - it explains why
lithium carbonate is used so often in spite of the problems that can arise.
Boron is very useful for some glazes in the lower stoneware temperatures
because it has such a low expansion rate below certain percentages. It is
difficult for instance to make a craze free glaze at cone 6, 7 and 8
without magnesium - boron is the answer for many of them.
Many glazes are far from a eutectic - relying on oversupply of certain
oxides for certain effects - how to melt em is the question - many times
the answer is a strong melter (rather encourages melting) with a low
expansion - like B2O3.
All this gives an idea why boron became the replacement for lead of course.
Have I mis read your question?
RR
>I have pondered before on these pages about the necessity for including
>Boric oxide in one form or another in glazes which mature upwards from
>cone 6. With the disappearance from suppliers shelves of Gerstly Borate I
>did wonder if people would abandon boron in this temperature range and
>rely totally on the group 1 and 2 fluxes.
>
>I have always found the rhetoric of glaze maturing theory to be confusing.
>It seems incongruous to be told that materials used in glaze recipes,
>especially those containing Sodium, Potassium and to a lesser degree
>Calcium, melt because of low solidus temperatures -Eutectics- and then
>find that so much Boron substance has to be included to get a recipe to
>work.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Ray Aldridge on wed 14 jun 00
Just as an addendum to what Michael is saying here: I recently did a fair
amount of work with C8 glazes that didn't use boron, mostly because I was
beguiled by Nigel Wood's descriptions of classic Chinese glazes.
Here's what I discovered in a brief period of time working with boron-free
glazes. Although it was perfectly feasible to get a good shiny melt at C7,
I had difficulty in developing a glaze fluid enough to level any marks from
the glazing process. If the glazing wasn't perfect, the fired glaze would
show blemishes.
I'm probably misunderstanding Michael, or my shaky grasp of glaze mechanics
is about to become obvious, but I didn't have the problem of high expansion
glazes in this range-- rather, I had the opposite problem. In fact, I was
a bit concerned about shivering in this kind of glaze.
G-200 44
Flint (Quartz) 21
Wollastonite 22
EPK 13
This glaze was the starting point for my experiments. I eventually began
to add whiting and frit 3134 to it to get the right texture and flow, and
also the whiting raised the expansion enough that I wasn't as worried about
shivering.
Ray
At 07:09 PM 6/14/00 +1200, you wrote:
>I don't think melting is the issue , Ivor. The Group I & II oxides promote
>fusion just fine above (or below) cone 6, but the resulting glazes have too
>high expansions to fit normal clay bodies. Boric oxide has extraordinary
>low expansion, so using it as a flux and glass-former enables the high
>expansion alkalis to be kept to lower levels.
>
>Leave out boron if you don't mind a lot of crazing, otherwise you might just
>have to resort to it. This is just one reason boron is useful in mid-fire
>glazes. Others include it's ability to dissolve alumina while maintaining a
>lower fluidity than silica/alkalis alone, lustre, unique colour response,
>desirable textural (e.g. floating texture) and blush effects.
>
>Michael Banks,
>Nelson,
>NZ
>
>
>Ivor Lewis wrote:
>----- Original Message -----
>> I have pondered before on these pages about the necessity for including
>Boric oxide in one form or another in
>> glazes which mature upwards from cone 6. With the disappearance from
>suppliers shelves of Gerstly Borate I did
>> wonder if people would abandon boron in this temperature range and rely
>totally on the group 1 and 2 fluxes.
>
>> I have always found the rhetoric of glaze maturing theory to be confusing.
>It seems incongruous to be told that
>> materials used in glaze recipes, especially those containing Sodium,
>Potassium and to a lesser degree Calcium,
>> melt because of low solidus temperatures -Eutectics- and then find that so
>much Boron substance has to be
>> included to get a recipe to work.
>
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melpots@pclink.com.
>
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Ken Chin-Purcell on thu 15 jun 00
Ron,
You write,
> Mostly potters use what seems to work - quick answers - it explains why
> lithium carbonate is used so often in spite of the problems that can arise.
What material is most preferable to lithium carbonate?
-- Ken Chin-Purcell
thansen@DIGITALFIRE.COM on sun 18 jun 00
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In industry fast-fire glazes are all the rage and they are much lower in
boron that in the past. Traditional frits like Ferro 3134 and 3124 melt
early and body gases are forced to bubble up through them. Fast fire
glazes melt quickly after decomposition gases are gone and you can get
perfect glaze surfaces even firing on greenware. Frits like Fusion F300
are a good start. There is a case to be made the ceramic suppliers do
not have a good selection of modern frits and supporting information
for thier customers.
At the same time lots of research is going into incorporating borates
into bodies for lower fire stoneware.
====================================================
T o n y H a n s e n thansen@digitalfire.com
http://digitalfire.com Calculation/Database Software for Ceramic Industry
http://ceramicsearch.com Search engine for the Ceramic Industry
--
--==__==__A8420XZ382__==__==--
thansen@DIGITALFIRE.COM on sun 18 jun 00
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> I re-read the =
> article by Dr. Richard Eppler, Formulating Glazes =96 CM Vol 47 No. 6. =
> June-August 1999. Quite detailed and might be regarded as required =
> reading for anyone learning about glazes. His statements about Boron =
> confirmed my own opinion. I had only one problem with the article. =
I spend a few days with Mr. Epplier last week and together we are
working on something pretty exciting. His advice and opinions are going
to be a lot more accessible in the coming year. He is kind of the Ron
Roy industrial ceramics, just as helpful and, do I dare say it, no I better
not!
--
====================================================
T o n y H a n s e n thansen@digitalfire.com
http://digitalfire.com Calculation/Database Software for Ceramic Industry
http://ceramicsearch.com Search engine for the Ceramic Industry
--
--==__==__A8420XZ382__==__==--
Ron Roy on mon 19 jun 00
I think Tony was going to say "just as old" it was wise of him to abstain.
RR
>I spend a few days with Mr. Epplier last week and together we are
>working on something pretty exciting. His advice and opinions are going
>to be a lot more accessible in the coming year. He is kind of the Ron
>Roy industrial ceramics, just as helpful and, do I dare say it, no I better
>not!
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Ron Roy on tue 20 jun 00
The problem in answering your question is - it's a simple question with a
complicated answer. Lithium is a strong alkaline flux - similar in most
ways to sodium and potasium. The big difference is it has a much lower
expansion rate than both. This can lead to some glazes having a very low
expansion - a dangerous situation because shivering - flakes of razor sharp
glaze) is the last thing you want your customers to find in their ware - or
food. Also lithium is the most soluble of the carbonates we use and the
migration of lithium (from the carbonate) can cause weird fit reactions -
like shivering and crazing on the same pot.
Yes, I know - that was not the question but it's not a simple subject. The
reason the carbonate is used is because it's a relativly insoluble source
of a strong flux - no other oxides come with it - seems like an ideal
solution to those that don't or won't use the tools we have to solve the
problem another way. Just dump in some lithium and get instant fluxing - at
even earthenware temperatures.
Simple answer for the simple approach to glaze technology and you get the
alkaline colour response as well.
So I can say there is nothing else in the same catagory.
I say get your lithium - if you must use it - from petalite or spodumene
and understand if it is necessary - and remember - there is a toxicity
issue involved.
I once suggested to a group of potters who were glazing bowls with an
obviously unstable Barium glaze - to test it by letting their new puppy
drink water from a bowl glazed with it. They were outraged - even though
one of them had given a set to her husband with the same glaze on them -
true story!
RR
>You write,
>
>> Mostly potters use what seems to work - quick answers - it explains why
>> lithium carbonate is used so often in spite of the problems that can arise.
>
>What material is most preferable to lithium carbonate?
>
>-- Ken Chin-Purcell
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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