Tom Buck on sun 8 sep 02
Hey, Wanda:
where-ever, whomfrom did you find this recipe? It is most unusual,
and it is an expensive way to get a copper blue at C6...two frits at US$5
per 1000 grams. Yet, it is a fine example of what not to do, namely, avoid
standard limits but still expect the glaze to behave as if it were a
standard-limit glaze.
and when a Clayarter seeks a response to a query for this mix:
20%w FF3110; 34%w FF 3289; 4%w Lithium carbonate; 10%w EPKaolin; 27%w
SiO2; plus 5%w copper cabronate
then the use of a glaze calculation program sheds some light on the
problem.
First stage analysis yields this Seger Flux Unity Formula:
BaO 0.27 B2O3 0.31 SiO2 4.65
CaO/MgO 0.11 Al2O3 0.28 Ratio SiO2/Al2O3 = 16.7
Li/K/Na oxides 0.62 Ratio SiO2+B2O3/Al2O3 = 17.7
And 0.2 moles of CuO will be there too.
COE/CTE : Bailey/Hewitt: 4.3 micometres per metre per degree Celsius
Insight value: 6.8 x 10-6 m/m.oC
These expansion numbers hint that the glaze will fit a stoneware body,
perhaps even a porcelaineous stoneware body. But as John H said earlier,
this presumes 1) the glaze is fired to maturity and 2) no crystallines
form in the melt as it cools.
The Seger (above) confirms that the glaze is outside standard
limit for silica, namely 4.65 moles versus 3.5 moles for Cone 6. Also, the
high levels of alkalis (Li/K/Na oxides) and Boric Oxide are difficult to
be compatible with the Alumino-Silica glass made from 0.28 moles Al2O3 and
2.80 moles of SiO2 (a common ratio).
The mole percentages also will reinforce this notion of poor
design: Silica, 74.5%m; alumina, 4.5%m; boria, 4.9%m; alkalis, 10%m;
barium oxide, 4.3%m; alkaline earth oxides, 1.8%m. None of our raw
materials (eg, Cornwall Stone) come close to these percentages. Hence, it
is hard for this mix to become "good glass".
There is every likelihood that two glass phases will be present in
the melt, an alumino-silca glass, and an alkali-boria glass, and that
these two glasses will not cool as a uniform glass on the pot. and some
crazing will be the result.
Ok. How to revise? This might suit:
Cone 6 Oxidation Copper Blue
12 Strontium carbonate
43 G200 fs.
20 Gerstley borate
5 Lithium carbonate
20 Silica (flint, quartz)
5 Copper carbonate
If a Gerstley Borate with a 1997 analysis is used, the Seger comes out
like this:
SrO, 0.27 Al2O3 0.32 SiO2 2.88
CaI/MgO 0.26 B2O3 0.25
Li2O, 0.22; K2O, 0.14; Na2O 0.11 Ratio Si/Al = 9; Si+B/Al=9.8
The COE/CTE calculates at 4.5 (B/H values). The Seger and the COE suggest
good glass with a fit on stoneware body. However, there is room for more
silica should crazing occur at the body/glaze interface.
now let the "yes/no" comments begin. Peace. Tom.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
Wanda Holmes on mon 9 sep 02
Tom, thank you for a great post - got me thinking bright and early this
morning! Let me clear up a couple of things and then I have a follow-up
question for you.
1) When I pasted the recipe into my email, I left off one ingredient.
It also has 9% whiting. Sorry to everyone for that mistake. GlazeChem
gives an analysis for this glaze of:
Na2O 0.26
K2O 0.02
MgO 0.00
CaO 0.36
Li2O 0.17
BaO 0.19
Al2O3 0.20
B2O3 0.22
SiO2 3.33
P2O5 0.00
TiO2 0.00
Fe2O3 0.00
Al:Si=1.00:16.63
Neut:Acid=1.00:7.96
A:N:A=1.00:0.42:3.33
Expansion: 73.5
It falls outside John & Ron's limits by being a bit short on alumina.
It also contains barium which they discourage. It falls well within the
limits given by Cushing, with the exception of the barium being high.
2) The cost of the glaze, given my local material costs is US$1.99/kg.
I admit it's a bit high, but I haven't been trying to optimize for cost
at this point.
2) Don't blame anyone for passing around a bad recipe. I made it up
myself and I'm the first to admit my inexperience. I started with one
of Ian Currie's corner glazes (90% 3134, 10% kaolin) and worked out a
number of experiments. The glaze above gave a beautiful color and
clear, bright glass, hence my desire to 'fix' it.
Now, for my question. With the corrected recipe is your comment about
two glass phases still applicable?
Thanks,
Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Tom Buck
Sent: Sunday, September 08, 2002 10:37 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: copper blue glaze
Hey, Wanda:
where-ever, whomfrom did you find this recipe? It is most
unusual, and it is an expensive way to get a copper blue at C6...two
frits at US$5 per 1000 grams. Yet, it is a fine example of what not to
do, namely, avoid standard limits but still expect the glaze to behave
as if it were a standard-limit glaze.
and when a Clayarter seeks a response to a query for this mix:
20%w FF3110; 34%w FF 3289; 4%w Lithium carbonate; 10%w EPKaolin; 27%w
SiO2; plus 5%w copper cabronate
then the use of a glaze calculation program sheds some light on the
problem.
First stage analysis yields this Seger Flux Unity Formula:
BaO 0.27 B2O3 0.31 SiO2 4.65
CaO/MgO 0.11 Al2O3 0.28 Ratio SiO2/Al2O3 = 16.7
Li/K/Na oxides 0.62 Ratio SiO2+B2O3/Al2O3 = 17.7
And 0.2 moles of CuO will be there too.
COE/CTE : Bailey/Hewitt: 4.3 micometres per metre per degree Celsius
Insight value: 6.8 x 10-6 m/m.oC
These expansion numbers hint that the glaze will fit a stoneware body,
perhaps even a porcelaineous stoneware body. But as John H said earlier,
this presumes 1) the glaze is fired to maturity and 2) no crystallines
form in the melt as it cools.
The Seger (above) confirms that the glaze is outside standard
limit for silica, namely 4.65 moles versus 3.5 moles for Cone 6. Also,
the high levels of alkalis (Li/K/Na oxides) and Boric Oxide are
difficult to be compatible with the Alumino-Silica glass made from 0.28
moles Al2O3 and 2.80 moles of SiO2 (a common ratio).
The mole percentages also will reinforce this notion of poor
design: Silica, 74.5%m; alumina, 4.5%m; boria, 4.9%m; alkalis, 10%m;
barium oxide, 4.3%m; alkaline earth oxides, 1.8%m. None of our raw
materials (eg, Cornwall Stone) come close to these percentages. Hence,
it is hard for this mix to become "good glass".
There is every likelihood that two glass phases will be present
in the melt, an alumino-silca glass, and an alkali-boria glass, and that
these two glasses will not cool as a uniform glass on the pot. and some
crazing will be the result.
Ok. How to revise? This might suit:
Cone 6 Oxidation Copper Blue
12 Strontium carbonate
43 G200 fs.
20 Gerstley borate
5 Lithium carbonate
20 Silica (flint, quartz)
5 Copper carbonate
If a Gerstley Borate with a 1997 analysis is used, the Seger comes out
like this:
SrO, 0.27 Al2O3 0.32 SiO2 2.88
CaI/MgO 0.26 B2O3 0.25
Li2O, 0.22; K2O, 0.14; Na2O 0.11 Ratio Si/Al = 9; Si+B/Al=9.8
The COE/CTE calculates at 4.5 (B/H values). The Seger and the COE
suggest good glass with a fit on stoneware body. However, there is room
for more silica should crazing occur at the body/glaze interface.
now let the "yes/no" comments begin. Peace. Tom.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
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dennis mclaughlin on sun 19 mar 06
Yesterday I was discussing glazes with a friend who was telling me about a copper blue cone ten reduction glaze she used to use but has since lost the recipe.
She thought it was called "H and H Copper Blue".
I checked the clayart archive which sometime proves to be very helpful with a search like this but I had no success.
Does this sound familiar to anyone?
I continue to enjoy the varied discussions that take place on the clayart.
-Denny
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