Earl Krueger on mon 2 aug 04
To see the effects of adding various amounts of
RIO and Cobalt Carbonate in one glaze go to:
http://www.duckfootpottery.com
then select "Glaze Tests" on the left.
Earl K...
Bothell, WA, USA
David Hendley on mon 2 aug 04
There is no reason to make ugly harsh blue glazes. There are
plenty of beautiful blue glazes. Here are some tips for making
blue glazes you can be proud of.
1 - As Mel mentioned, add iron oxide along with the cobalt.
Unless you want an garish blue-on-blue, add much less
cobalt and more iron than the MLB secret recipe.
My rule of thumb is to add twice as much red iron oxide
as cobalt carbonate. Start with small amounts - .20 (that's
point (.)20 percent) cobalt carbonate will give a nice blue in
many glazes. It is believed that the mineral added to ancient
Chinese glazes had iron oxide naturally occurring with the
cobalt. By adding RIO with the cobalt you are simply
duplicating that mineral with modern refined ingredients.
2 - For a very light delicate blue with no specks, put a
tube of cobalt blue watercolor paint in your clear glaze.
Of course, you will have to figure out how much to use for
the color intensity you want. Using cobalt carbonate and
especially cobalt oxide, it is hard, unless you ball mill
your glazes, to get a delicate light blue with no dark blue
spots.
3 - As Mel also said, add chrome oxide along with the
cobalt. My rule of thumb for these ingredients, for teal
blue, is equal amounts of cobalt oxide and chrome oxide.
If you use cobalt carbonate, use 1/3 less chrome oxide.
BTW, it is also helpful to add cobalt to the chrome oxide
when you are formulating chrome green glazes. My rule of
thumb for forest green is to add half as much cobalt
carbonate as chrome green.
4 - For dark cobalt blue glazes (with the added iron oxide
of course), add some granular illmenite to add visual
texture and break up the surface. Gold specks on a dark
blue background is beautiful. Suggested amount is .17%
(that's point (.) 17 percent, a tiny, tiny amount), added after
sieving the glaze.
5 - Best of all are the non-cobalt blue glazes, with rutile or
titanium blue glazes topping the list. Usually about 3 to 5%
rutile will produce rutile blue, but these colors are, unlike
cobalt blues, sensitive to the glaze formula and firing
conditions.
6 - Stains. There are some very pretty Mason or Cerdac
stains. The color you see is the color you get. Try some
of the non-cobalt blue stains - my favorite is vanadium-
zirconium turquoise.
I work at cone 10 reduction - relationships and addition
amounts may well be different for different firing conditions.
No Blue Christmases for me. I make a point of using
plenty of nice looking non-blue glazes. Blue is still my
biggest selling color, but not by much.
There are a lot of people who do not like blue pottery.
Ron Roy would rather have a cup with an oxide-leaching
copper glaze than to have to look at a cobalt blue glaze.
David Hendley
david@farmpots.com
http://www.farmpots.com
Tig Dupre on wed 4 aug 04
Earl,
That's a LOT of work! Not just the pots, which is painstaking work enough, but the web pages as well. My, we have some talent in this venue!
Thanks for all the comparisons, the well-presented results, and for your generosity in sharing all of it.
Tig Dupre
in Port Orchard, WA, USA
Ron Roy on wed 4 aug 04
Yes - I admit that blue is not one of my favorite colours - in fact almost
my lest favorite - there are certain yellow greens that turn my stomach.
I would never have any disrespect for anyone who does blue pots however. To
foucus on one of the more superficial aspects of a pot - like colour -
seems to me to be missing the point.
I have some blue pots in my collection - they are exceptional pots - they
are exceptional pots to me even though they are blue.
I do prefer the sunrise and sunset to the miday sky - I thought everyone does???
If I had to sum up my feelings about blue - the colour of the sky shades -
I would have to say - isn't there enough already?
RR
>There are a lot of people who do not like blue pottery.
>Ron Roy would rather have a cup with an oxide-leaching
>copper glaze than to have to look at a cobalt blue glaze.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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