search  current discussion  categories  glazes - cone 8-10 

cone 10 glaze results

updated sat 4 jun 05


John Britt on fri 3 jun 05


As you know from reading my book, especially the =93Overview of Glazes=94, I=

selected glazes in use across the country as well as some of my glazes and
finally glazes that were submitted by the artists in the book. I tired to
show a range of possibilities within the glaze type chart. So, more than
being just a recipe reference, I tried to make the charts a learning tool.

You can see many things by studying them. In the Temmoku chart you see
that most contain feldspar, silica, whiting and clay. They all contain
iron, from 7 =96 11 % (approx.). A few contain zinc oxide, gerstley borate
and barium carbonate.

Yes, the 0.1% silica in Hamada Rust is probably unnecessary. I put it in
primarily because it is on the teapot on page 71 and also because this
glaze is in between a temmoku and a tessha (one definition =96 a =93rust col=
that covers at least 50% of the pot=94.)

Its inclusion also helps you to notice how different this recipe is from
the other temmoku=92s, in that it contains 12.4% gerstley borate. In fact,
this base is more like Pete=92s Red or Peach Bloom 2 listed in the =93Copper=
section. It is a copper red base recipe with iron added.

This illustrates what Mel and Joe Koons did in their Iron Saturate
investigation (Ceramics Monthly article - March 2005). They took base
recipes like Pete=92s Red and left out the colorants and added various
amounts of iron. Notice their recipe Iron Saturate #15. It lists silica at
1%. Very similar to Hamada Rust!

So that is why I put recipes like these in the book, so you could
recognize them in other places.

A good exercise would be to take the recipe chart from their article (page
65 Ceramic Monthly March 2005) and retotal all the recipes with Iron Oxide
below the 100% line and Zinc Oxide above the line. This will give you a
standard to compare. Then try to find the same bases in my book. You will
see that #10 is similar to Glick Red, #16 is similar to John=92s Oil spot
#3, etc. See how many you can find!

As for the Buttermilk, in the =93White=94 section, it is a magnesium matte
glaze fluxed with gerstley borate (10.5 %) again. So it will give teadust
effects since magnesium oxide is what causes these. Yes, you can add other
colorants and an infinite variety of results. If you are getting rose and
mauve I would assume you are firing in reduction because that is the
effect of copper oxide.

As for the John=92s Red, I would think you either slightly under fired it or=

applied it too thin on the exterior and that is why it is clear/ gray.
Also this is typical of using it on a stoneware body. (Gray) So you may
just try it again and see the results. Try it on porcelain!

Hope that is helpful and glad you like the book. There is a lot of
information in the book that you will find if you really read it. You need
to fire and see the results and then read again. Then compare. Fire again,
etc. There are layers and layers of information.

Great job and glad you liked the results!

John Britt

I fired my kiln Monday(Memorial Day) loaded with my pots and glazes
from your book. I used three that "I" thought would be easy, safe, fun and
material I had on hand.
First let me clarify that I am not a glaze person. I usually go by what I
read or people give me.

My first question is about a glaze called Hamada Rust (page 70).
This formula calls for 0.1% silica. Is this a typo or does it get enough
silica from the feldspar. It seemed like a really low amount to even
bother with if it gets it somewhere else.

Second question/comment, Buttermilk(page 63). I added 3% copper carb to
this and got a wonderful rosy, mauve, teadust looking result. Whitish
speckles over the mauve/rose, purple where thick. Surface looks/feels semi-
matte. Just wondering if you have played with this.

I also fired Johns Red. Got mixed results. Inside the pots are a bright
tomato red, outside, red/rose with what looks like clear gray where the
copper burnt out.
Not displeased with any of them, just thought I would ask about the one
and share about the others. The book has been a real treat. Loads of


I should add I fired these glazes on Standard 182 clay, propane fired
light reduction. Since this was my first firing I am not completely sure
about the reduction cycle. I do not have a oxy probe. I relied on what I
have learned at the local Art Center, and a really good friend who used to
fire there kilns.