May Luk on mon 24 nov 03
Hi all;
I am comparing a few Tin Chrome Glaze in my computer. What is the subtotal
alkalis number in relation to total fluxes? It's the percentage of alkalis
in the total fluxes? I suppose it's a quick glance guide to see if it's
within limits [0.25 % in unity?]
Other than that, what's the purpose of seeing different values of total
alkalis in different recipes? To predict colour responses?
I'm getting potter's dictionary in the post [a thanksgiving present to
myself] I'll look it up in the book when I get it. Meanwhile, I appreciate
any input to this premature question.
Many thanks
May
London, UK
P.S. I was reading the recipes and the calculated numbers of different
tin-chrome glaze before I went to sleep. In my dream, I tested 4 recipes and
they all come out green in my sleep.
P.S.S. My pots are not in the Morley Exhibition with Russel, but my "work"
is with every pots in the show. I made all the labels that went on the pots.
eheh!
John Hesselberth on mon 24 nov 03
Hi May,
Since I know you have GlazeMaster, I will assume you are talking about
the subtotal alkalis number that is calculated within that program. It
is just the total of sodium, potassium, and lithium numbers above it.
And yes, predicting color response is one use for it. In recipes
containing no lithia, you might want to match the Na + K total without
worrying too much about the individual levels when substituting
ingredients. Also some authors talk about KNa as if they were
one--since relatively few recipes have lithia in them this is the same
as KNa for most recipes. As we learn more (and here I am speculating)
you might be able to predict the activity of the flux system by looking
at that number or the ratio of alkaline earths to alkalis.
Regards,
John
On Monday, November 24, 2003, at 05:55 AM, May Luk wrote:
> I am comparing a few Tin Chrome Glaze in my computer. What is the
> subtotal
> alkalis number in relation to total fluxes? It's the percentage of
> alkalis
> in the total fluxes? I suppose it's a quick glance guide to see if it's
> within limits [0.25 % in unity?]
http://www.frogpondpottery.com
http://www.masteringglazes.com
David Hewitt on wed 26 nov 03
May,
This is an interesting question with more than one answer.
Mike Bailey in his book 'Glazes Cone 6' illustrates one usage very
clearly.
If you are seeking to produce a Cone 6 shiny transparent glaze without
using boron, then the Seger formula wants to be 1:.2 to .4:2.5 to 3.5,
fluxes alumina, silica.
It is also important to get the fluxes right - alkalis/alkaline earths.
The alkalis should not exceed .5 parts and the alkaline earths should
not exceed .75 parts.
He shows two recipes:-
T10
China clay 30
Whiting 30
Quartz 40
fluxes alumina silica
0.02 K2O 0.34 Al2O3 2.93 SiO2
0.01 Na2O
0.97 CaO
alkaline earths are 97 parts
At cone 6 this is semi-opaque matt
T11
High alk frit 60
China clay 20
Quartz 20
fluxes alumina silica
0.34 K2O 0.30 Al2O3 2.92 SiO2
0.50 Na2O
0.16 CaO
alkalis are 84 parts
At cone 6 this runs on vertical surfaces and crazes badly
The more you go above cone 6 the greater the fluxing power of the
alkaline earths. T10 might be quite a good cone 9 glaze.
There is also the question of colour response, the alkalis giving
brighter colours.
In message , May Luk writes
>Hi all;
>
>I am comparing a few Tin Chrome Glaze in my computer. What is the subtotal
>alkalis number in relation to total fluxes? It's the percentage of alkalis
>in the total fluxes? I suppose it's a quick glance guide to see if it's
>within limits [0.25 % in unity?]
>
>Other than that, what's the purpose of seeing different values of total
>alkalis in different recipes? To predict colour responses?
>
>I'm getting potter's dictionary in the post [a thanksgiving present to
>myself] I'll look it up in the book when I get it. Meanwhile, I appreciate
>any input to this premature question.
>
>Many thanks
>May
>London, UK
>
>P.S. I was reading the recipes and the calculated numbers of different
>tin-chrome glaze before I went to sleep. In my dream, I tested 4 recipes and
>they all come out green in my sleep.
>
>P.S.S. My pots are not in the Morley Exhibition with Russel, but my "work"
>is with every pots in the show. I made all the labels that went on the pots.
>eheh!
--
David Hewitt
David Hewitt Pottery
South Wales UK
Web:- http://www.dhpot.demon.co.uk
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