Ron Roy on thu 12 jun 97
KKP wrote -
"This is in the interest of ending the hysteria and making dumb
replacements of Ba with Sr -- they're not much alike at all, you know."
KPP
This is the 1st part of my answer re strontium as a good substitute for
Barium. It covers the use of up to 10 percent Barium in WHITE OR CLEAR OR
SEMI-OPAQUE LINER GLAZES used for functional ware. To get that amount of
barium oxide into a cone 10 glaze you would need any where from 11 to 13
percent of Barium Carb in your recipe. Over that amount it is possible to
have Barium matte (read non-functional) glazes and I will talk to that in
the 2nd part of my answer.
Actually these are not my answers - I am quoting from two of the best
Ceramic Technology books I have - Ceramics Glaze Technology by Taylor &
Bull (CGT for short)
a Ceramic Glazes by Parmelee and Harman (CG for short.)
Keep in mind there are two ways in which Strontium and Barium are similar.
They are both middle temperature fluxes (unless fritted when they are more
usable at lower temperatures) with Strontium fluxing a little lower than
Barium. Both have similar expansion with Strontium's being a bit lower. We
can say roughly the same thing about Calcium oxide as well - a mid range
flux with a similar expansion to SrO and BaO. The other mid range fluxes
are ZnO and MgO but which have a lower expansion.
Quote from page 23 (CGT) "The use of Strontium in conjunction with Barium
and Calcium gives benifits beyond what might be expected from the mixed
base effect when there is a need to control crystallization. In direct
comparison with Barium oxide alone , Strontium oxide produces brighter and
more fusible glazes."
"recent investigations have consentrated on the non -hazardous nature of
Strontium based glazes"
"The commercial aspects of the use of Strontium compounds are related to
those of Barium and Calcium because these elements have similar properties
and are often substiuted for Strontium."
"(Strontium Carbonate) has the advantage over Barium Carbonate of being
non-poisoness."
Also - in relation to a statement about Strontium on the list re changing
in a glaze - ".. can be used ............ in raw glazes dispite its slight
solubility in some grades of water.
CG page 41. "Clark concluded that superior glazes could be had by using
strontia for replacing some of the other bases......." "The opinion is
expressed that the use of strontia as a replacement for calcia and baria
will promote a more satisfactory interfacial reaction with a resulting
better glaze frit. It is expected that there will be a greater scratch
resistance and lower solubility in water and other fluids commonly brought
into contact with tableware."
Sounds to me like Strontium is a very interesting oxide to use in making
durable table ware - perhaps even better than Barium? It certainly melts
better and usually lowers expansion a bit which is of particular interest
to those trying to make hard glazes at c6.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/ronroy.htm
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