Daniel Semler on sat 6 may 06
Maiolica query
Hi May,
Found this rather interesting. I can't I'm afraid offer much on
earthenware as
I know v. little about it. As to best melt it seems that you are in an ideal
position to develop that first hand, from the plot and the glaze test results.
I have a question though. I am assuming that the mole ratios are mole
percents
? Is that so ? On this point, the new Understanding Glazes by Eppler
and Obstler
was interesting. They state that use of mole percent is better at earthenware
temps as many usual stoneware/porcelain fluxes normal counted as RO
(fluxes) in
the Seger formula are refractories at low temps. Anyhow given this, it may be
interesting in respect of best melt to also note mole percent of flux - what's
too much, too little for your taste or purpose.
Thanx
D
May Luk on sun 7 may 06
Maiolica query
Hello Daniel
Yes, it was mole percentage. I have no fluxes in mind
when I plot the graph. I used mole % because it is
easier to graph. In theory, I can use unity or wt %.
They are essentially the same graphical
representation. I plot this graph so that I can see
which direction I should take regarding materials*.
That is why I asked for the best melt area in the
first place. I see that I would have to do the 4
corner grid test.
Thanks for the note. I appreciate it. I went and look
at traixial graph and its application**. At this
point, it’s beyond my cognitive load. (ie, to include
RO in my graph and how to INTERPRET it.) It appears
that I have to get some phase diagrams or some data of
the best balanced area.
For the most part, I don’t know how to work in mole %,
except RR taught me to keep an eye on it when I have
to round off the numbers in unity. I will plot the
triaxial graph and see if I get something just from
doing it. The 7 glazes had been fired. Luckily I had
the graph template made already when I was studying
David Hewitt’s booklet a few years back. Then I will
go back to read your note again (about the fluxes) and
see if I can make it out. Physically doing is the best
way to learn, I reckon.
Many thanks for your interest
May
*Michael Bailey, Oriental Glaze, Chapter 8 – plotting
the raw materials
**http://www.dhpot.demon.co.uk/, click on Eutectics &
Phase Equlibrium Diagrams
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
[...]
I have a question though. I am assuming that the mole
ratios are mole percents? Is that so ? On this point,
the new Understanding Glazes by Eppler and Obstler was
interesting. They state that use of mole percent is
better at earthenware temps as many usual
stoneware/porcelain fluxes normal counted as RO
(fluxes) in the Seger formula are refractories at low
temps. Anyhow given this, it may be interesting in
respect of best melt to also note mole percent of flux
- what's too much, too little for your taste or
purpose
Daniel Semler
Ivor and Olive Lewis on sun 7 may 06
Dear Daniel Semler,=20
I found your remarks about the comments of Eppler and Obstler =
interesting.
Perhaps you could provide me with the biblio information for this book =
so that I can access it via our travelling library.
I would like to read their opinions about the formulation of low =
temperature glazes and the benefits that accrue from using refractory =
compounds in low temperature melting glazes.=20
It seems to me that if an ingredient is refractory it will have a low =
level of solubility and remain undissolved in the silicate melt. This =
will increase opacity. It may also affect the durability of a glaze. =
Certainly, if the vitreous portion of the glaze is deficient in these =
materials both viscosity and surface tension as well as transparency =
might be affected.=20
Do E and O suggest that the full recipe should be fully fritted prior to =
application ? Perhaps this may be a necessary step in the production of =
low temperature glazes.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Daniel Semler on mon 8 may 06
Hi Ivor,
Here are the details :
Title : Understanding Glazes
Authors : Richard Eppler with Mimi Obstler
Paperback: 300 pages
Publisher: American Ceramic Society (October 30, 2005)
Language: English
ISBN: 1574982222
That said I do not think that they particularly recommend that materials that
are low temp refractories ought to be used, but rather that they felt
there was
more general applicability of mole percent in calculations. Of course you are
correct that it would only be a problem if there were such materials in
a given
formula. I am not sure that you will find much on this in the book though. I
found the comment interesting in that I had asked precisely the question as to
why one would prefer one representation over another some time ago.
As to fritting, much of the discussion relates to industrial products, as it
were, and fritting is assumed for most of the low fire glazes. The discussion
of colour is interesting in that ir is largely confined to the use of
industrial fritted pigments and the chemical requirements of the base glaze.
This is not a subject I have had any previous experience with.
BTW, they discuss how a glaze melts and state that the glaze has components
which melt and others that disolve in that melt, altering the propoerties of
the melt as they do so. I think you've put this forward before too. It seems a
reasonable explanation to me.
Overall I think its a fabulous book. I've almost finished reading it and I'm
now looking at the example glazes in the final chapter. I did find that
some of
the photographs were less than clear. It has extensive references which is
always a good sign.
Thanx
D
Daniel Semler on wed 10 may 06
Maiolica query
Hi May,
Thanx for this.
I'm not sure that you need to go to phase diagrams and so on. I guess
that all
I'd say is that you need to be able to define what it is that you mean
by "best
melt" or "best balanced" and be able to determine if you've hit it with any
given glaze. Perhaps visual inspection is enough. Perhaps you want to use some
chemical test. I'm not dead sure what your aim is. Are you looking for durable
glazes, are you looking for a certain kind of surface, do you just want to
ensure that the glazes are not underfired ? Just things to think about.
If your
just exploring the glaze space then perhaps the plots themselves will reveal
something interesting in that way.
Good luck, thanx
D
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