Caroline and Hedley Saunders on mon 25 may 98
I would really appreciate some help from the wonderful glaze guru's on =
Clayart
as I do not have direct access to a glaze chem. teacher. I am using Rhodes,
Clay and Glazes for the Potter and Hamer, The Potter's Dictionary of =
Materials
and Techniques as my main sources of reference.
I am trying to learn about glaze chemistry and have been playing with the
following recipe, (the original by Emmanuel Cooper uses flint instead of
quartz):
Feldspar 55
Dolomite 5
Barium Carbonate 20
Quartz 10
China Clay 10
Copper Carbonate 2=25
I do not have any glaze calculation software but am reasonably competent at
mathematics=21 Do I need to put the copper carbonate into the calculation =
to look
at the unity formula? By my reckoning, without the copper carbonate, I get =
a
unity formula of 1 : 0.618 : 3.463
What I am doing is taking each ingredient in turn and substituting something
else to see what happens. I don't want to do the calculations on the test
recipes until I know whether or not to include the copper carbonate=21
Caroline....who actually quite likes playing with sums =3Cg=3E
delphin=40eclipse.co.uk
Paul Lewing on tue 26 may 98
Caroline and Hedley Saunders wrote:
> I am trying to learn about glaze chemistry and have been playing with the
> following recipe
> Feldspar 55
>
> Dolomite 5
>
> Barium Carbonate 20
>
> Quartz 10
>
> China Clay 10
>
> Copper Carbonate 2%
>
> I do not have any glaze calculation software but am reasonably competent at
> mathematics! Do I need to put the copper carbonate into the calculation to lo
> at the unity formula? By my reckoning, without the copper carbonate, I get a
> unity formula of 1 : 0.618 : 3.463
Caroline,
You don't need to include the copper in the unity formula. In fact,
many calculation programs (for whatever reason, I've never been sure)
don't even iclude colorants in their materials databases. In this
case, there isn't really enough of it to affect the chemistry much
anyway. Where colorants seem to affect your glaze the most is in
coefficient of expansion, as many of them have COE's that are
radically different from most other glaze ingredients. But you
wouldn't get a COE figure by doing the math with a calculator anyway.
You need a program for that.
I don't have time to run this recipe through one of the programs I
have, but .618 seems like a very high figure for the R2O3 column. It
would be way outside the limit formulas for Alumina, and I don't see
where you would be getting that much Al from this recipe. You might
run that again.
Also, that's a lot of Barium. It may give you problems in mixing it
up, and it very well may not be food-safe.
> What I am doing is taking each ingredient in turn and substituting something
> else to see what happens.
A great idea, and one of the best ways to learn about glaze materials!
Another series of tests you should run for your education is to cut
each material in half and add it back in increments till you have
double the amount the recipe calls for.
Happy Testing
Paul Lewing, Glaze Guru Wanna-Be
Ron Roy on tue 26 may 98
Hi Caroline,
I don't usually include colourants - unless they are iron or rutile - don't
have my calculator set up for copper, cobalt etc. - it does not seem to
interfere with solving glaze problems. Here is my calculation of that glaze
using analysis of the materials I can get here. Feldspars vary as does
China clay and dolomite - so that may account for the differences. If you
want to send me the analysis for the materials you are using I can give you
a better idea of how accurate your calculations are.
I am assuming this is a cone10 matt glaze and it is oversupplied with
Barium - you will have to have it tested to see if it will leach
significant amounts of Barium into food. It may also discolour when in
contact with some foods. It also looks like it will craze on most bodies.
-----------------
G 200 SPAR.......... 55.00 55.00%
BARIUM CARB......... 20.00 20.00%
DOLOMITE............ 5.00 5.00%
SILICA.............. 10.00 10.00%
EPK................. 10.00 10.00%
----------
100.00
FORMULA & ANALYSIS
------------------
*BaO........ .40 16.98%
*CaO........ .14 2.22%
*MgO........ .10 1.15%
*K2O........ .25 6.44%
*Na2O....... .11 1.81%
Fe2O3...... .00 .15%
TIO2....... .00 .03%
AL2O3...... .54 15.16%
SiO2....... 3.38 56.04%
P2O5....... .00 .01%
RATIO 6.28
EXPAN 656.98
WEIGHT 361.94
I'll be happy to check your calculations for you.
>----------------------------Original message----------------------------
>I would really appreciate some help from the wonderful glaze guru's on Clayart
>as I do not have direct access to a glaze chem. teacher. I am using Rhodes,
>Clay and Glazes for the Potter and Hamer, The Potter's Dictionary of Materials
>and Techniques as my main sources of reference.
>
>I am trying to learn about glaze chemistry and have been playing with the
>following recipe, (the original by Emmanuel Cooper uses flint instead of
>quartz):
>Feldspar 55
>
>Dolomite 5
>
>Barium Carbonate 20
>
>Quartz 10
>
>China Clay 10
>
>Copper Carbonate 2%
>
>I do not have any glaze calculation software but am reasonably competent at
>mathematics! Do I need to put the copper carbonate into the calculation
>to look
>at the unity formula? By my reckoning, without the copper carbonate, I get a
>unity formula of 1 : 0.618 : 3.463
>
>What I am doing is taking each ingredient in turn and substituting something
>else to see what happens. I don't want to do the calculations on the test
>recipes until I know whether or not to include the copper carbonate!
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
BobWicks on tue 26 may 98
In a message dated 5/25/98 9:15:08 AM Eastern Daylight Time,
delphin@eclipse.co.uk writes:
<<
Feldspar 55
Dolomite 5
Barium Carbonate 20
Quartz 10
China Clay 10 >
Caroline:
I'm not going to try and explain here what would take a full text book to give
you what you want. You have already figured out that the base ingredients add
up to one hundred. It is accepted practice not to use the color agents in the
percentage batch.
To start in making any explanation on this subject you must place all
ingredients that have OR, R2O in the flux category. An example of this would
be CaO. Needless to say these numbers you have here represent a percentage
batch not a unity formula. You will note that the unity formulas that Dan
Rhodes uses indicate fractional parts of a molecule. These are expressed as a
decimal. Also note that when figuring out a unity formula all of the
fractional parts of a molecule in the FLUX column must be made to add up to
one molecule. How do you do this?
List all in gradients categorized as fluxes (or bases,RO,R2O) in one list.
List all ingredients categorized as a refractory (neutrals, R2O3) in one list.
List all glass formers or (acids, RO2).
If the decimals in the flux column do not add up to one full molecule then
divide each number in the list by total of the list to give you a new number
which should add up to one. Also divide each ingredient in the neutral column
by the total of the base column and also do the same for those falling in the
acid (RO2) column.
Ok I have now explained part of the answer you asked about. Now you will have
to learn how to calculate a raw compound into the numbers that Rhodes is
using. I suggest that get a book dealing solely on Glaze calculation. You
might try to get Glaze Calculations by McFee. You have your work cut out for
you.
Good Luck
Bobwicks@aol.com
Craig Martell on tue 26 may 98
>I am trying to learn about glaze chemistry and have been playing with the
>following recipe, (the original by Emmanuel Cooper uses flint instead of
>quartz):
>Feldspar 55
>Dolomite 5
>Barium Carbonate 20
>Quartz 10
>China Clay 10
>Copper Carbonate 2%
>I do not have any glaze calculation software but am reasonably competent at
>mathematics! Do I need to put the copper carbonate into the calculation to
look
>at the unity formula? By my reckoning, without the copper carbonate, I get a
>unity formula of 1 : 0.618 : 3.463
Hello Caroline:
Here is what my calculation is for your receipe.
Untitled Recipe 1
POTASH FELDSPAR 55.00 BaO 0.40*
DOLOMITE 5.00 CaO 0.11*
BARIUM CARBONATE 20.00 MgO 0.11*
SILICA 10.00 K2O 0.39*
KAOLIN 10.00 Al2O3 0.54
======== SiO2 3.29
100.00
Cost/kg 0.15
Si:Al 6.09
SiB:Al 6.09
Expan 8.70
When looking at the first column, which are the fluxes, the number 1 means
nothing unless you break all the fluxes down into their molecular
contribution to the glaze. Above, the starred oxides, or the first four in
the column are the fluxes and add up to "1". What you see is that there is
a lot of barium in relation to some of the other fluxes. There is a fair
amount of Potassium as well. But for food use, there is too much barium in
this glaze and you would only want to use it on surfaces that will not
contact food. The alumina is a bit high for the cone 6 range but OK for
cone 10. The silica is at a good level for cone 6 and at the low end of
normal for cone 10. The caluculated expansion is high, and this glaze will
craze on most claybodies.
What a unity formula shows, when it is in RO or in flux unity, is the
molecular relationship between one molecule of flux and whatever molecular
amounts of alumina and silica there are in the formula. In this particular
glaze, the one molecule of flux is divided into parts of barium, potassium,
calcium, and magnesia, and you can see which oxides are the major players in
the glaze. This can be looked at in the limit formulas for certain
temperatures to see if the fluxing oxides, alumina, and silica are within
the parameters for a balanced durable glaze. Also, our calculations differ
a bit because we are probably using different analyses for spar and kaolin.
It is important to use the most current analysis for any of the raw
materials in a glaze. I also don't know if the glaze calls for potash or
soda feldspar, as you just give "feldspar" in your receipe.
Almost forgot, you don't need to add the copper into the calculation, and
the other oxides add up to 100% without it anyway.
I hope this is of some help. I've just covered the basics really and there's
a lot more info to digest on the Unity or Seger formula to use it to your
advantage when going for specific types of glazes and color response etc.
regards, Craig Martell-Oregon
Ron Roy on wed 27 may 98
Yes you can - simply calculate the % oxides in a glaze then multiply by
what ever factors you want to use - I use the English and Turner set - (#7)
from Mike Mike Baily and David Hewitt article on expansion in Ceramic
Review #113 - 1988.
It could be reproduced on Davids IMC page at http://digitalfire.com and go
to people then to David Hewitt.
David can be reched by email as well.
snip > But you
>wouldn't get a COE figure by doing the math with a calculator anyway.
>You need a program for that.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Fay & Ralph Loewenthal on wed 27 may 98
Dear all glaze gurus, I am not so well up on the unity
formula. I was told by my pottery teacher that any barium
glaze with copper will leach. Apparently the copper does a
very nice job on helping it leach out. This is besides the fact
that this glaze submitted by Caroline has got more than
enough barium to leach out. The thread some months,
maybe years ago sort of indicated that more than 6 or 7%
would leach out. Please let me know if I am on the correct
track. Ralph in PE SA.
David Hewitt on thu 28 may 98
In message , Paul Lewing writes
>You don't need to include the copper in the unity formula. In fact,
>many calculation programs (for whatever reason, I've never been sure)
>don't even iclude colorants in their materials databases.
The absence of colouring oxides in some glaze programs has always
intrigued me too. I have always assumed it is because of the general
practice of developing a base glaze first, using a glaze program if you
have one, and then perhaps a line progression series of test glazes with
the colouring oxides added. However it is so easy to have the colouring
oxides added in the glaze program data base in the first place, that it
seems illogical to not include them. They are certainly not inert
materials and in the case of red iron oxide, for example, can be very
significant according to the the firing conditions. Also, as you say,
they do affect the coefficient of expansion.
>In this
>case, there isn't really enough of it to affect the chemistry much
>anyway. Where colorants seem to affect your glaze the most is in
>coefficient of expansion, as many of them have COE's that are
>radically different from most other glaze ingredients.
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Ron Roy on thu 28 may 98
Hi Ralph,
It is not so simple as that - many factors are involved. It is the
durability of the glaze which determines how much leaches out. It is more
likely that more will come out if there is more to start with - but - even
a glaze with only a small amount of say Barium - if not formulated to be a
good glass - can leach significant amounts - and it is widely reported that
lead glazes leach more when copper is present - and I assume this is true
for other glazes as well - but don't know that.
The good part about having small amounts of toxins in a glaze (if there is
a good part) is that it takes a shorter time to get all of the leachable
toxins out.
There is much misinformation around it seems - we love the simple answers
but this is not a simple science. We are making headway however - I hope
you all realize just how important this CerMatech thing is - and about
time.
It is important that those who are promoting this valuable information
source be given the support and encouragement they need to continue. I am
hoping there will be a journal of the talks - I will certainly encourage
them to do that.
>----------------------------Original message----------------------------
>Dear all glaze gurus, I am not so well up on the unity
>formula. I was told by my pottery teacher that any barium
>glaze with copper will leach. Apparently the copper does a
>very nice job on helping it leach out. This is besides the fact
>that this glaze submitted by Caroline has got more than
>enough barium to leach out. The thread some months,
>maybe years ago sort of indicated that more than 6 or 7%
>would leach out. Please let me know if I am on the correct
>track. Ralph in PE SA.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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