Lili Krakowski on wed 27 jul 05
Someone asked about a speckled Robin's Egg Blue.
This recipe--from Beth Molaro via the Gibbes Museum Studio, is a lovely REB.
Kaolin 12
silica 24
Pot spar 32
Zinc Oxide 8
Whiting 24
add Rutile 7
Cobalt CARB .5
Tin Ox. 7.5
Now. We have had several questions/remarks/observations about Glaze
Testing, and I would like to address here some of its aspects.
Here is a really pretty glaze that worked well. In my 24-year old notes it
names a pot spar no longer to be had. TIME TO TEST.
Ok. Good reason to test. You try the potash spar YOU have. See how IT
works. If you do not yet have pot spars "in depth" you might want to get
ahold of 2 lbs of each your dealer sells, and see how they work in this
glaze. Good reason to test.
Now the inquirer wanted speckles. And we know (don't we) that cobalt OXIDE
tends to GIVE speckles, and that it often is rejected , and the carbonate
used, to avoid speckles. So here is ANOTHER reason for testing. We ALSO
know that granular rutile gives specks. Well 7% of granular rutile might
be overkill, but a nice straight line blend using granular at one end, and
powdered at the other might yield pleasant surprises.
Now we get to tin. The tin is essential to the look of this glaze. I have
argued before--oh so many times--that while tin is pricey, it is totally
worthwhile in the greater scheme of things. (You do the math, as the nonce
phrase has it! Around here 1 lb tin = 3 lattes)
However. I find it written nowhere that this glaze HAS to have 7.5% tin.
Maybe, just maybe, that glorious satin look could be achieved with only 5%
tin and another opacifier making up the balance. No idea. ANOTHER reason
to test.
BUT! Wait up a minute! I only have used this glaze over a bland buff
body. (NO, did not apply as makeup. Shoulda said CLAY body.! N'est ce
pas, M. Clennell?) If you work on a white body, it may contain talc--i.e.
magnesium--and that may affect the blue. And if you use a dark red body,
who knows what might happen. So you DO want to test over the clay you are
using, and over a white slip on that clay....Another reason to test.
And last you do want to know about fit. Crazing. Like that. ANOTHER
reason to test. And I have only used this in a regular old style electric
kiln, low/medium/high type, so you with the new digital ones may want to
check out some more stuff.
What I am driving it, dearly beloved Newbies, is that testing is not done in
a vacuum. It is done for reasons. Of which several above. And it is a
waste of time and money, and taxing on one's enthusiasm and patience to test
test test (those 480 tiles still give me nightmares) without having a
specific, and relatively narrow goal in mind. Just don't do it.
Now one more test you might like to make, and which I think valid.
The rutile/tin/cob.carb "colorant" may work beautifully in a glaze you
already have. NB that this recipe contains zinc, but neither boron, nor
magnesium. so if you already HAVE a glaze like that, why not give that
colorant combo a whirl.
Or you might want to reach out and use a recipe that DOES contain magnesium,
but NO zinc and see what the colorants do.
PLEASE NOTE. This calls for one half percent, a teeny tiny amount of
cobalt, you may not get quite right in a 100 gram test.
PS: I DO mean "dearly beloved Newbies." Those of you who are sincere and
really interested and really want to learn are wonderful. As to those who
check in for a "freebie" consultation without wanting to learn...that is
THEIR tragedy, now ain't it--because they probably take this attitude
towards other things in life as well.
Lili Krakowski
Be of good courage
Ron Roy on thu 28 jul 05
This one is short of silica as well - so it will not be a stable glaze -
which means it may - under certain conditions lose colour in places - or
maybe all over.
Best not to use it as a liner glaze - and it will craze on most pottery clays.
RR
>Someone asked about a speckled Robin's Egg Blue.
>
>This recipe--from Beth Molaro via the Gibbes Museum Studio, is a lovely REB.
>
>Kaolin 12
>silica 24
>Pot spar 32
>Zinc Oxide 8
>Whiting 24
> add Rutile 7
> Cobalt CARB .5
> Tin Ox. 7.5
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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