David Hewitt on wed 26 mar 97
I think that this is a most interesting question and I wish I knew the
answer. Borax is also a glass former, so you could, perhaps, also ask if
it should be included as Acidic.
If you use limit formulae you need to have a common basis for these
figures when analysing a glaze. To include the B2O3 as Amphoteric has
become the most common approach for its inclusion and so, in the absence
of any contrary approach being developed, this has the virtue of
being consistent.
If you use triaxial phase diagrams for plotting glaze analyses, the same
question arises. The point on the graph changes significantly when the
borax is added and,so of course, does the performance of the glaze.
Mike bailey and I are currently carrying out some glaze tests for Cone
5-6 glazes. We are starting with recipes that do not include borax and
then adding the same amount of a borax frit to each recipe. We have
started from the known eutectic area on the triaxial diagram for cone 8
glazes and altered the basic oxides to be strong in alkali fluxes, K2O,
Na2O and Li2O and also ZnO. We have had no difficulty in getting a range
of glazes that range from matt to satin to very shiny. The next step is
to add the borax frit and see how these change.
In time I would hope to be able to add something more positive to this
discussion.
In message , Mo Cain writes
>----------------------------Original message----------------------------
>It is not my intent to start an ongoing debate but does anyone have an
>easily understood rationale for sometimes including B2O3 in the RO
>column for the Seger Unity analysis and sometimes including it in the
>RO2O3 column? It seems to me that for any given batch recipe analysed
>either way (B2O3 a flux and B2O3 not a flux) it would lead to different
>theoretical formulae and presumably different limits for each ingredient
>yet the actual glaze is the same in either case. Is this a big deal or
>am I barking up the wrong tree? I am relatively new at this analysis
>lark and I am somewhat bemused by the fact that batch recipes are
>carefully weighed out in grams to two decimal places and the unity
>formula calculated often to three decimal places and yet to get the
>glaze to work I sometimes have to add a little bit of this or subtract a
>little bit of that and generally fiddle about and usually ending up with
>something entirely different. From my discrete lurking position I
>recognise that there are some mighty sharp folks out there in Clayland
>so I anticipate some further insight into what for me is a mystery.
>
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
URL http://digitalfire.com/education/hewitt.htm
Rick Sherman on thu 27 mar 97
Where to put borax? David Hewitt is correct. Whether you place it in
the RO or the R0203 column, be consistant. I have always considered
it a flux and been happy with my tests. Since it is soluable, I used
to make my own frit when using the stuff. Now there are more
commercial frits containing borax. It seems to help elminate crazing
in some glazes. RS
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