Daniel Semler on fri 2 jun 06
Hi All,
Thought I'd toss this one out there for two reasons, 1) it was a blast to see
it work, 2) it needs some tweaking, and 3) I thought there might be some
interest. Be warned this is a long lab report.
So I have as I'm sure you're sick of hearing recently finished reading
Understanding Glazes by Richard Eppler and Mimi Obstler. In the back they
design glazes for specific properties coming up with a formula first and then
converting it to a recipe, explaining as they go why they picked a particular
material for some oxide or other.
It finally occurred to me that I could try that. So here it is.
I wanted a glaze that :
- would be a satin matte
- would fit Glacia porcelain - a very low expansion cone 10 clay body
- would be well melted
- would be able to take cobalt to make a very pale purple
So here's what I came up with initially :
Al2O3 0.5
SiO2 3.5
MgO 0.25
CaO 0.5
KNaO 0.25
After playing with it a little I ended up with :
CaO 0.07*
Li2O 0.14*
MgO 0.29*
K2O 0.14*
Na2O 0.07*
Al2O3 0.50
SiO2 3.52
SrO 0.29*
As you can see most of the calcia has been traded for strontia and lithia, to
lower the expansion.
So can I explain my choices ? Here goes and leap in and tell me I'm nut at any
appropriate point.
The key thing about hitting a satin was picking an Al:Si ratio. 5 is matte and
10 is gloss so I figured 7 was good for satin. I also wanted enough of Al2O3 and
SiO2 to ensure a reasonbly durable glaze. 0.5 alumina at cone 10 seemed good and
so that left me with 3.5 silica. As I used custer spar as a rule and had a bunch
around it seemed sensible to use it. To counteract its high expansion I used
Aussie spodumene, the lithia lowering the expansion. This gave me a base to
work with.
Next the fluxes. KNaO (from the spar) is high expansion, so lower expansion
fluxes were required from here on. MgO was a natural choice to help there. It
also turns out that MgO tends to favour purples from cobalt, so I'd read. I
wanted to see if that worked out, so I made sure I had a bunch of it but was
worried that if I had too much I might end up with crawling. I also wanted the
stain quality often associated with MgO containing materials, like dolomite,
talc and so on. Following that, I was concerned to have decent melt for the
glaze and have read/heard that a diversity of fluxes will aid melting. So I
added another one that I've been playing with lately, strontium carbonate.
So I had chosen custer spar, aussie spodumene, talc as the MgO source rather
than dolomite because I wanted to avoid the CaO expansion, and strontium
carbonate. So now I had all the ingredients to sit rock hard on the bottom of
the bucket, and to be pretty friable when dry on the pot. So some clay (EPK)
was added, as I needed the alumina anyway. Finally silica to make up the rest
of the required silica.
My recipe then when balanced to match my formula and desired expansion was
this :
CUSTER SPAR................. 36.80
SILICA...................... 13.40
EPK......................... 11.20
TALC........................ 11.20
AUSI SPOD................... 15.20
STRONT CARB................. 12.30
=========
100.10
The molecular formula differs a bit from my original envelope sketch being :
CaO 0.07*
MnO2 0.00
Li2O 0.14*
MgO 0.29*
K2O 0.14*
Na2O 0.07*
Fe2O3 0.00
TiO2 0.00
Al2O3 0.50
SiO2 3.52
P2O5 0.00
SrO 0.29*
Fluxes are MgO 0.29, KNaO 0.21, SrO 0.29 and Li2O 0.14 plus odds and sods.
Silica/Alumina ratio is bang on. COE calculated is 433 which is about what I
need for this body.
Next I made up three batches, one plain, one with 5% tin oxide and 0.25% CoCO3
and, one with 5% zircopax and 0.% CoCO3.
So the results. Well the colour is off. First its far to strong. I wanted very
pale. Secondly its very blue, not purple enough. However, on the upside the
glaze is a beautiful satin, very nice to the touch, and well melted. It appears
to be craze free but I'll need to really check that and being a satin its a
little hard to tell straight off. The one with tin oxide was not so much to my
taste but I very much liked the plain and the zircopax ones but as I said a
little too much cobalt.
So I need to work on the colour. No surprise there. Otherwise it was something
of a revelation that it can be done and it does work.
If you've got this far, the cone 10 redux fired samples can be viewed here
Thanx
Daniel
Ivor and Olive Lewis on sat 3 jun 06
Dear Daniel Semler ,
Congratulations on taking that giant step forward.
Pleased to see you are supporting our local economy. I prefer Petalite. =
One of the "Double Whammy" compounds when it comes to controlling C.o.E, =
having both Lithium and Silicon Dioxide.
I have been unable to borrow the Eppler/Obstler book but I was =
interested in your comment "...that a diversity of fluxes will aid =
melting..." Did this come from their book. If it did I would be =
interested to know how they argue the theory that supports this view. It =
is a thing that I have read before and wondered where it originates.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
If you have not already had your hands on it I would suggest your next =
step is to access Greg Daly's book, "Glazes and Glazing Techniques" ISBN =
0-86147-502-7
Daniel Semler on sat 3 jun 06
Thank you Ivor,
The "diversity of fluxes" is a thing I've heard around the traps for a while.
I don't believe I've ever come across data demonstrating it. I'd been meaning
to experiment with it for some time. Of course I'd need a properly designed
test to demonstrate it, and currently I'm doing another big test series so
it'll have to wait I'm afraid.
I double checked the Eppler/Obstler book and a quick look doesn't turn up a
comment on this. Parmalee makes the following statment in "Maturing the Glaze"
on p221, "Increasing the number of different bases employed in the glaze will
generally lower the maturing temperature and extend the firing range
throughout
which it will be serviceable. Since these characteristics are the
result of the
presence of eutectics as well as other chemical and physical conditions, the
above mentioned effects are not necessarily present in all cases." I think Ron
has mentioned this sort of thing on the list before, in respect of glazes
bearing multiple feldspar bases and such.
So many tests so little time :) That said the literature contains a
great deal
of work on such things already. I would think that someone might have already
done this bit of testing.
And yes I already have Greg Daly's book. Been a while since I looked into it.
Thanx
D
Taylor Hendrix on sat 3 jun 06
Daniel,
Your exercise is an EXCELLENT illustration of the power of Segar
formulation for developing glazes. Fantastic work. Not only do you
use the power of unity formulation you follow it up with one of the
potter's bestest friends, empirical testing.
I'm going to get my hands on a copy of that book now. Thanks for
letting us in on your work.
Taylor, in Rockport TX
On 6/2/06, Daniel Semler wrote:
> Hi All,
>
> Thought I'd toss this one out there for two reasons, 1) it was a blast to see
> it work, 2) it needs some tweaking, and 3) I thought there might be some
> interest. Be warned this is a long lab report.
>
> So I have as I'm sure you're sick of hearing recently finished reading
> Understanding Glazes by Richard Eppler and Mimi Obstler. In the back they
> design glazes for specific properties coming up with a formula first and then
> converting it to a recipe, explaining as they go why they picked a particular
> material for some oxide or other.
>
> It finally occurred to me that I could try that. So here it is.
>
> I wanted a glaze that :
>
> - would be a satin matte
> - would fit Glacia porcelain - a very low expansion cone 10 clay body
> - would be well melted
> - would be able to take cobalt to make a very pale purple
>
> So here's what I came up with initially :
>
> Al2O3 0.5
> SiO2 3.5
> MgO 0.25
> CaO 0.5
> KNaO 0.25
Ivor and Olive Lewis on sun 4 jun 06
Dear Daniel Semler,
Thank you for your message.
You confirm my expectations. I have read Parmellee and Parmellee and =
Harmond, which was the second edition.
Seems to me that given a Eutectic is the "Lowest point at which melting =
will take place" claiming that there are other such events of eutectic =
melting in the maturation of a glaze is illogical.
Singer and Singer, "Industrial Ceramics" give some wonderful information =
relating to "Deformation Eutectics" which is enlightening. The original =
information about this concept is worth exploring. I read their =
reference material. Well worth the cost and effort.=20
Keep up the good work.
Best regards,
Ivor
Ron Roy on wed 7 jun 06
Hi Daniel,
Just to let you know I saw both this one on your web site and the Kona
experiment - good of to post them - you are doing a great service to all by
doing these I think.
I think it was Louis Kats who said - add a new flux and you automatically
get more melting.
I makes sense to me but don't ask me why - I'm sure there are people around
who can explain why - I certainly know it's true when you sub in Li2O for
KNaO.
Keep up the good work - just was working on the CA itinerary - beginning to
get a slight buzz about the trip - we will drive up to Seattle and fly back
from there.
Best regards - hope all is well with the family - RR
> The "diversity of fluxes" is a thing I've heard around the traps for a while.
>I don't believe I've ever come across data demonstrating it. I'd been meaning
>to experiment with it for some time. Of course I'd need a properly designed
>test to demonstrate it, and currently I'm doing another big test series so
>it'll have to wait I'm afraid.
>
> I double checked the Eppler/Obstler book and a quick look doesn't turn up a
>comment on this. Parmalee makes the following statment in "Maturing the Glaze"
>on p221, "Increasing the number of different bases employed in the glaze will
>generally lower the maturing temperature and extend the firing range
>throughout
>which it will be serviceable. Since these characteristics are the
>result of the
>presence of eutectics as well as other chemical and physical conditions, the
>above mentioned effects are not necessarily present in all cases." I think Ron
>has mentioned this sort of thing on the list before, in respect of glazes
>bearing multiple feldspar bases and such.
>
> So many tests so little time :) That said the literature contains a
>great deal
>of work on such things already. I would think that someone might have already
>done this bit of testing.
>
> And yes I already have Greg Daly's book. Been a while since I looked into it.
>
>Thanx
>D
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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