Laura Conley on tue 16 jun 98
I am confused about lead silicates. The ratios of lead to silica (and alumina,
etc.) that I see in ceramics textbooks do not agree with the ratios shown in
Laguna's catalog. I called them to confirm that their numbers are not just typo
I expect lead bisilicate to have 1PbO 2SiO2. Laguna shows 1 PbO to 3 Al2O3 to
195SiO2. Could there really be 195 silica to every lead?????? Is lead really t
strong a flux?
Similarly, lead monosilicate is 1PbO 67SiO2 according to Laguna, whereas I find
to 1SiO2 in books.
Help!!!!
Now I don't trust my notes on lead sesquisilicate...
Laura Conley
Boulder, CO (getting ready to teach that glaze class...)
Tony Hansen on thu 18 jun 98
>I called Laguna to confirm that their numbers are not just typo
>I expect lead bisilicate to have 1PbO 2SiO2. Laguna shows 1 PbO to 3 Al2O3 to
>195SiO2. Could there really be 195 silica to every lead?
>Similarly, lead monosilicate is 1PbO 67SiO2 according to Laguna
The books are right.
Lead bisilicate is about 1 part lead to 2 parts silica, usually closer
to 1 part lead, 1.8-1.9 silica. Lead mono is equal parts.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
Edouard Bastarache on sun 10 aug 03
Hello all,
according to A.E.Dodd in Dictionary of Ceramics,
lead silicate comprises a group of lead frits.
"It is a material obtained by fritting lead oxide with
silica in various ratios.
The usual ratio is PbO.2SiO2 and a frit of this
composition is known as "lead bisilicate".
so-called lead monosilicate is approx. PbO.0.75SiO2.
Tribasic lead silicate, 3PbO.SiO2 finds some use in
making lead glasses.
The bilisicate is used in pottery glazes, enamels, etc."
I have not found any information concerning the hazardous=20
decomposition products for "lead bisilicate" in the=20
documentation I have at hand except, one MSDS
supplied by our friends at Potterycrafts in the UK.
It is stated on it that there is no hazardous decomposition
products.
Still, you will have to test your utilitarian wares for lead=20
leaching in accordance with local regulation.
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
iandol on wed 13 aug 03
Dear Friends,
As seems to be the norm in ceramic arts circles we are not getting the =
complete picture of what happens when Lead Oxide is associated with =
Silicon Dioxide to create a glaze worthy compound.=20
It seems to me that there is a broad assumption about the "stuff" we =
process. It is being assumed that the only thing "stuff can do is to =
melt and mix, then form a glassy material called a frit or glaze when =
such mixtures cool. It is an assumption which ignores the potential for =
Chemical Reactions between Chemical Compounds.
Those who have access to the relevant phase diagram (Fig 284 System =
PbO-SiO2 in the 1979 A.C.S Atlas) will see that there is potential for =
three Chemical Reactions between Litharge and Quartz. These give rise to =
chemical compounds which have PbO to SiO2 ratios of 4:1, 2:1 and 1:1. Of =
these, Lead Meta silicate: O3PbSi *, has a melting point of 764 deg C =
and Lead Ortho Silicate: O4Pb2Si *, has a melting point of 743 deg C. A =
mixture of these two compounds exhibits a Eutectic temperature of ~720 =
deg C which contains molecular values of approx 15% PbO - 85% SiO2 and =
might be called, as a milled ingredient of its parent compounds, Lead =
Sesquisilicate. Greenwood and Earnshaw report of another compound =
PbSi2O5 while Levin et al show Beta 4PbO.SiO2 which may be another =
compound to consider..=20
So, my Friends, where do we go from here?
I am wondering if people who are employed by Universities to teach =
Ceramic Arts ever think to go to the Uni library and have a look along =
the shelves given over to other subjects, or if they ever approach =
members of other faculties to check their thinking before going into =
print. Or are they content to rely on Rhodes, Hamer, Lawrence, Etc for =
knowledge?
** My way of expressing the Formulae? Alphabetical in Element order. =
Stop for a while. Try not to think in terms of Molecular Oxides!!
Best regards to all,
Ivor Lewis. Redhill, South Australia
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