Jorge Nabel on wed 8 mar 06
Dear Clayarters, I need some advice coming from experience.
After a Currie grid , we developed a bunch of Iron Saturate ^6 glazes.
They range from caramel to metalic grey,to black. You know, the standard.
We refired some of them to bisque (1000C)and those closer to corner C
turned yellow.
Some changed from black to brown. But, in the only one firing we have
no records of,
when refired they turned a gorgeous RED. Of course it never happened again.
Since this happened, some months ago, I have read archives, hammer, some
other books
concernig iron cristals,etc,but couldnt duplicate the red.
Corner C is 40% Nepheline, 40% alkaline frit and 20%dolomite. plus 15%RIO
Someone says it depends on fast first firing with enough heat, others
say go slow,
and so on.
I began to learn some chemistry in order to understand. But so far, no clue.
Anyone has experienced this?
Anybody out there,still at home?
Thanks, Jorge en Buenos Aires (so humid and full of mosquitoes)
Des & Jan Howard on thu 9 mar 06
Jorge
You didn't mention if you are using an electric or gas kiln.
If it is an electric kiln with a programmable controller try this
refiring cycle.
Fire to about 1020C
Fire down to 920C over 4 hours, then 720C over 4 hours, then kiln off.
Do the refiring as its own cycle, don't include the refires along with a
biscuit firing.
Bone ash added to high iron glazes can produce tomato reds in oxidation.
I can't give you amounts for ^6 glazes, ^10 reds usually match the
RIO & bone ash, eg 10% RIO + 10% bone ash, 15% RIO + 15% bone ash.
I've refired ^10, ^11 & ^12 glazes fired in electric & gas kilns under
oxidation or reduction & find that some of the zappiest results occur from
slow cooling around the temps I indicated (G'donya Hank!).
Des
Jorge Nabel wrote:
> Dear Clayarters, I need some advice coming from experience.
> After a Currie grid , we developed a bunch of Iron Saturate ^6 glazes.
> They range from caramel to metalic grey,to black. You know, the standard.
> We refired some of them to bisque (1000C)and those closer to corner C
> turned yellow.
> Some changed from black to brown. But, in the only one firing we have
> no records of,
> when refired they turned a gorgeous RED. Of course it never happened
> again.
> Since this happened, some months ago, I have read archives, hammer, some
> other books
> concernig iron cristals,etc,but couldnt duplicate the red.
> Corner C is 40% Nepheline, 40% alkaline frit and 20%dolomite. plus 15%RIO
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
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