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tom sawyer's cone 10 to cone 6 glaze conversion

updated tue 26 jun 01


John Post on sat 23 jun 01

Hi Tom,
I ran across this old post from Ian Currie while looking through some =
glaze information I had saved. It's a post about developing a Reitz =
Green at midfire. I believe you requested some info about this =
recently. =20

I highly recommend Ian's book Revealing Glazes.... especially if you are =
trying to convert some cone 10 glazes down to cone 6. I think his grid =
method is an excellent way to explore glazes...You can learn about =
glazes on both the recipe and molecular formula level using his =

I would also get a copy of Robert Wilt's Glazchem software. It's a mere =
35 dollars and it does all of the things the more costly programs do. =20

I tested the glaze that Ian mentions below and got a nice matt blue =
green at cone 7
Here it is...
+++ Reitz/Currie Midfire Green +++
EPK 13.2% =20
Frit 3110 21.7% =20
Frit 3134 3.5% =20
Whiting 5.2% =20
Spodumene 8.7% =20
Nepheline syenite 47.7% =20
------ =20
100 % =20
Cobalt carbonate 1 % =20
Rutile 3 % =20

Chemical Analysis =20

Na2O 0.48 Al2O3 0.66 SiO2 3.27
K2O 0.10 B2O3 0.07 TiO2 0.12
MgO 0.00 Fe2O3 0.01
CaO 0.32 =20
Li2O 0.07 =20
CoO 0.03 =20

Alumina:Silica ratio is 1.00 : 4.96
Neutral:Acid ratio is 1.00 : 4.67
Alkali:Neutral:Acid ratio is 1.00 : 0.73 : 3.39

Expansion coefficient: 89.6 x 10e-7 per degree C
Oxides causing abnormal expansion effects: Li2O B2O3

Good luck with it,
John Post

Ian's original post starts here>>>>
It was an attempt to produce a good Cobalt/Titanium green at midfire in =
with a stoneware Reitz Green as the starting point.

To cut a long story short, we got some very nice Reitz Green type glazes =
midfire, and also some that were merging into blue, and had very =
mottled blue where thick and matt green where thin.

The best result similar to what you describe was Glaze 21 on the grid.

The Glaze-C for the grid was:
55 Neph Syenite
10 Spodumene
6 Whiting
4 Ferro frit 3134
25 Ferro frit 3110
+1% cobalt carbonate
+3% rutile

This is NOT the glaze recipe. This recipe is the bottom left corner of =
grid, and contains zero clay and zero quartz. This recipe is used to
calculate all the other glazes in the grid.

To get the recipe for Glaze 21, go to my website:
and click on the "Calculation Page". Read the instructions there, and =
input this Glaze C into the appropriate boxes at the bottom of the page.
[The first 5 materials above are flux materials. The last 2 are =
and opacifier in that order. You need to know this to put them into the
correct boxes.] Then click the "Calculate Now" button. This will =
produce a
list of 35 glaze recipes - the recipes for the grid.

Alternatively, to get the recipe(s) you can use the tables in the back =
of my
new book: "Revealing Glazes - Using the Grid Method", which you can buy =
the above website.

Read off the recipe for Glaze 21. It MIGHT work! There are however =
potential traps between the result on my once-only-tried new grid and =
your student might mix up. Therefore I would recommend you/they mix up =
least all of the glazes around Glaze 21. (Look at the diagram at the top =
the "Calculation Page" - that shows the layout of the 35 glaze numbers.)

You could do the whole grid if you like, but for this glaze you are =
only interested in the left hand 1 or 2 vertical rows.

I could just give you the recipe for #21 of course, but your chance of
getting what you want is much less if I do that than if you follow the
instructions above. One of the features of the grid method is that it =
built in a range of values of alumina and silica that compensate and =
out for a whole heap of possible differences between what we mixed up =
what you or your student might mix. It also compensates to some degree =
firing and clay differences. The question becomes not "will the glaze
recipe work", but "are we lucky, and which of the 35 glazes will give =

And of course someone might just give you the recipe you want!! :) =
ever way... good luck

Ian Currie