Lili Krakowski on tue 3 jun 08
Barnard, a.k.a. Blackbird, disappeared from the market a good many (20?)
years ago. Some still have a batch stashed away here and there. However
there is no certainty that if you get a bag of the stuff from A it will be
the same as the bag B gave you.
Barnard was a natural clay, mined over many years, and varied a good deal.
As far as I know/knew Barnard was a red surface clay with a good dash of
manganese. (Vide infra. [I just love to use that phrase, gives me chills up
and down my spine!] )
BUT, looking up Blackbird/Barnard under Digital Fire--on whom all
blessings--their formula is:
CaO .600
K2O 1.100
MgO .700
Na2O .600
TiO2 .200
Al2O3 7.600
SiO2 47.00
Red Iron Oxide 33.9
Look, Ma, no manganese....
Turning then to my trusty notebooks (this is the Infra vided Supra)
Ron Roy, blessings on him too, gave this recipe for a Barnard Substitute on
Clay Art :
Red Art 56.6
Ball ClayOM4 18
Silica 25.5
Red Iron Oxide 23.5
Manganese Dioxide 5.5
Recipe Name: barnard sub
Unity Oxide
.026 Na2O
.384 K2O
.343 MgO
.247 CaO
1.000 Total
2.046 Al2O3
2.529 Fe2O3
17.059 SiO2
.149 TiO2
Glaze Master (TM) reveals this molecular formula. Note that the Manganese
is NOT calculated in.
So it seems to me that anyone who needs Barnard Clay in a recipe can just
recalculate, and anyone who wants Barnard can work with the substitute. I,
for one, have simply used Red Art plain, doctored with a bit of manganese.
Red Art goes like this:
Na2O .018
K2O .495
MgO .44
CaO .047
Al2O3 1.843
SiO2 12.248
Fe2O3 .505
TiO2 .152
This is what I have in my GlazeMaster records, BUT I do not know whether
this came with it, or whether I added it...so any errors in
composition...blah, blah.
As you can see you probably could conjure up something good with a high
magnesium glaze doctored with iron and manganese! BUT it would not have the
qualities of a slip glaze.
Good luck.
Lili Krakowski
Be of good courage
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