Francie Pusateri on mon 18 mar 96
I use two different Raku glazes that result in a nice turquoise
color, Higby High Water Blue "darker" and Utah Alkali Blue "lighter".
Both develop their color using copper carb as the
colorant. Unfortunately, I do not have the recipies here at the
office, but will forward them eventually. I can offer some
advice on how to get consistant turquoise color from glazes using
copper carb as the colorant.
1) The kiln atmosphere has to be in oxidation.
The best way to check with out an expensive oxygen probe is to
fire at night when you can see the color of the flame and the
extent that it reaches out of the flue. If you have visible flame
extending out of the flue, your kiln is in reduction. If the flame
is blue to lavender, it is in light reduction, if it is pink to orange,
it is in heavy reduction. We use a metal blower fan behind the burner
ports to add oxygen to put our kiln in full oxidation. You can see the
flames when a kiln is in reduction during the day, but it is more
difficult. A reduction atmosphere is fairly common with a propane
fired raku kiln.
2) The second thing you need to do is pull the piece and
let the glaze solidify prior to your post fire reduction. This can
be done by misting with a spray bottle similarly to how you would
handle a white crackle pot. I also put a small piece of kiln shelf
in the kiln while I fire the pots. Then once I have misted the pot,
I put the kiln shelf in the combustibles to start a good fire and
place the pot on the shelf. This prevents the pot from coming in
contact with the combustibles which will cause blossoms of copper
red and at the same time starts a good fire to blacken the clay
3) Another approach to gaining consitancy with turquoise raku
glazes would be to fire the pot in an electric kiln (c 05 for the
glazes I use) prior to firing in Raku kiln. Then fire in Raku
kiln to ~ c 012 to get the pot hot again prior to the post fire
A couple of things to consider. You probable will not get consistant
copper turquoise if you are using it in combination with glazes that
need a slight reduction atmosphere inside the kiln and mod/heavy post
fire reduction ie: copper matts. Other glazes that work well with
the above firing process are white crackles and other glazed that
do not need post fire reduction to develop their color, ie: the
post fire reduction is use to blacken the claybody.