[Clayart] Line blend shortcut: Is the "fast five" good enough?

[David Hendley]

----- Original Message ----- 
> I'm having trouble with my iron reds, which generally come out a deep
> maroon, rather than a ... well, iron red. I gather that I probably need to
> do a line blend, to see whether my RIO is the right strength. But here's
> what I want to know: Is Diana Pancioli's "fast five" test good enough, or
> do I need to do one percent increments, say from 1 to 10 percent RIO?
>
> FYI, I'm firing in an oxidizing atmosphere in a gas kiln, with a half-hour
> soak at about 1800 degrees, at the end. The clay is B-Mix or the 
> equivalent
> from another manufacturer.

I don't know what the "fast five" is, but I know that there is no point
in testing 1% or 10% RIO for an iron red glaze. All the iron red
glaze recipes I've seen have about 5-to-8 % iron red. An adequate
test would be, say, 4%, %5, 6%, 7%, 8%, 9% RIO.
I suspect, however, that the strength of the iron oxide is not your
problem, and that instead it is the glaze recipe of the firing.

David Hendley
david at farmpots.com
http://www.farmpots.com