Natalie Winter on tue 1 jan 02
Hi All
Here in frost-bitten England we've just celebrated the New Year, so all
my best wishes to all for a happy, healthy and prosperous 2002.
Heather (my partner) and I had planned to see in the New Year with a
floodlit raku session, but were defeated by the weather. I guess some of
the non-Brits here will call us wimps for giving up in a mere -7°C
(19°F), but here on the "English Riviera" (south Devon coast) such
temperatures are unprecedented -- ever since I've lived here, we've
never had a frost to speak of, and can keep our clay bins and glaze
buckets outdoors all year round. We now have a backyard full of frost-
bitten clay, but that's another story...
I saw in the New Year in the kiln room (where else?!) where just after
midnight I unloaded the final test firing of my latest glaze recipe
creation. I thought I'd post the recipe in case it's useful to anyone...
here goes...
This is a rather specialized sort of glaze, developed to accompany
crystal glazes (which are my great passion). Now, crystal glazes are
very runny, and you inevitably end up grinding dribbles of glaze off the
bottom of pots. On decorative ware, we finish off the ground surface by
sticking a felt pad to the base of the pot, but for functional ware we
wanted a better way of finishing off. I set out to develop a *very* low
temperature glaze that could be applied to the base after grinding, and
re-fired at a temp too low to harm the crystal glaze. It had to be non-
crazing and lead free, and my experiments showed that it would have to
fire no higher than 800°C to avoid disrupting all those lovely crystals
that have taken hours of firing-down to achieve... and we wanted it to
be an unobtrusive black color that would disguise any marks from
grinding or drops of glaze.
Incidentally, I reckon this might be useful as a raku glaze too. I've
tried fast-firing and crash-cooling it, and it holds up fine.
Here it is: NW90, "Cover-a-splodge" (!)
High Alkaline Frit (Potterycrafts 2962) 65
Calcium Borate Frit (Potterycrafts 2954) 30
Kaolin 5
Copper Carbonate 6
Cobalt Silicate (or carbonate) 6
Red Iron Oxide 6
This deliberately uses the colorants as additional fluxes to meet the
very low melting point requirement. The Ca/B frit is the magic anti-
crazing ingredient. I prefer the silicate of cobalt to the carbonate
because it's much less prone to specking, and at least in England it's
actually slightly cheaper than the carbonate too.
If anyone wants to make this with different frits, or maybe using
gerstley borate or colemanite instead of the Ca/B frit, the molecular
analysis of the glaze (sans colorants) is as follows:
.412 Na )
.371 Ca ) ( 1.48 Si
.153 K ) .139 Al ( .52 B
.062 Ba )
.002 Mg )
Hope this is useful (or at least interesting!) to at least someone.
Happy New Year!
Nali.
Natalie Winter
The Dawnmist Website:
http://www.dawnmist.demon.co.uk
Jocelyn McAuley on thu 3 jan 02
Hi Natalie,
This is a great idea. Thanks for sharing your glaze experiment
results with us. I have worked with crystalline glazes too, so its nice
to add this trick up my sleave!
I've played with reducing already fired crystalline pieces at this
temperature too. So perhaps rakuing the crystalline pieces with this
glaze on them would be interesting.
Good luck and thanks
Jocelyn
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon
http://www.ceramicism.com
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