Pat's Pottery on fri 7 sep 07
Hi,=20
My name is Pat and I am new to this list. I have a question about =
glazes and one in particular. I have read that all the glaze recipes =
should add up to 100 without the additions. I have two recipes for =
VAL'S TURQUOISE and they both only add up to 77/78 (see below). Am I =
safe in making this glaze, and could someone explain to me why some =
glazes don't add up?
VAL'S TURQUOISE (^5-9)
Custer Feldspar 27.6
Gerstley Borate 16.87
Flint 21.32
Whiting 8.82
Dolomite 2.9
Copper Carbonate 2.34
Bentonite .8
pale blue turquoise with a frost
Val's Turq. cone 6, oxidation.=20
Tested on mid range, iron flecked stoneware, fired to 1220c, oxidation.=20
Receipe=20
27.60 Custer spar=20
16.90 Gerstely Borate=20
21.30 Silica=20
2.90 Dolomite=20
8.80 whiting=20
ADD=20
0.8 Bentonite=20
2.3 Copper carb.=20
Subbed local spar for Custer=20
All percentages rounded up to the nearest whole percent.=20
Resulted in a stable, bright and clear, gloss turquoise glaze.=20
Iron flecks came clearly though glaze. Slight, slight steaking and =3D=20
pooling=20
in bottom half of test bowl. Not a big color or covering difference =3D=20
where double dipped.=20
Same receipe with G.Borate subbed with Colemanite produced same results =
=3D=20
as above=20
Same receipe with G.Borate subbed with local frit produced same results =
=3D=20
as above.=20
Personal:=20
A nice, smooth gloss with a good greenish turquoise color.=3D20=20
Without the colorants, this makes a nice white gloss
Ted Neal on sat 8 sep 07
Hi Pat
Glazes do not need to add up to 100...it is just a convention that makes life easier.
If it works as it should, and you like it, then you can retotal it to 100 with some simple math to
make future batches easier to mix and compare to other recipes
As you said remove, the additions (Copper and bentonite) and add up the first 5 ingredients
Custer, GB, Flint, Whiting and Dolomite divide each part by the total.
So if the total is 77.51
the new feldspar amount, divide 27.6 by 77.51 and you get .3560. Move the decimal over 2
places and you get 35.6
the new Gerstley amount, divide 16.87 by 77.51 and you get .2176. Move the decimal over and
you get 21.76.
Do the same for all the materials...and you new base recipe will be..
Custer 35.60
Gerstley Borate 21.76
Flint 27.50
Whiting 11.37
Dolomite 3.74
Just finish up by checking that they add up...should be 100 (or very very close. (99.97 in this case.
Then add back in the other modifying ingredients (colorants/suspender here) by figuring what %
they were in the original recipe by weight.
Copper carb was 2.34/80.65 (The total of all the original ingredients). Divide to figure the % by
weight. and you get .0290 or 2.9% copper
Figure Bentonite the same way .8/80.65 about .01 or 1% by weight.
So here is the new recipe
Custer 35.60
Gerstley Borate 21.76
Flint 27.50
Whiting 11.37
Dolomite 3.74
Add 2.9% Copper
Add 1% Bentonite
Of course there are programs out there - (Hyperglaze, Insight) that will do these calculations
instantly, but don't let a little math scare you. Remember this works because any number over
itself is equal to 1....so if you put each part of a total number, over the total, it gives you a
percentage of one...just move the decimal over to change that a percentage of 100.
Also you don't have to remove the glaze modifiers from the original before you retotal, this is also
a convention that makes it easier to read and compare recipes, but it in not necessary.
Best
Ted
Ted Neal
Ball State University
Maurice Weitman on sat 8 sep 07
Hello, Pat,
I don't know whether this will be helpful, but when I read your
query, the glaze looked familiar to me.
I found several references to it in the archives, one that I recalled
in the form of a response by the always informative Craig Martell way
back in July of naught-naught. I believe it provides useful info
about the "am I safe in making this glaze" part of your question.
Here it is:
>I retotalled this glaze to 100% and ran it thru my glaze program. For a
>cone 5-7 glaze it is within or close to the limits for various
>oxides. It's at the lowest recommended limit for alumina and just a tiny
>bit over the limit for boron so it may shift and run a bit if applied
>heavily. I see that this glaze has a firing range that extends above cone
>7 and into the 8-9 range. It's out of the suggested limits for alumina and
>silica for that temp. It's about .2 moles short of silica which isn't a
>disaster but copper will increase the solubility of the glaze somewhat so
>there may be some leaching and you won't be able to tell if it's ok without
>having it tested. My guess, and that's all it is, would be that this glaze
>is probably ok and if you lowered the copper to about 2% it would help.
>
>later, Craig Martell in Oregon
The link to it and two queries that prompted Craig to write is:
Here's a link to a clayart archive search (which might actually work,
depending on the height of the moon and how often you floss)
containing all mentions of val's turquoise. you'll note that all
recipes add up to the 77 or so number you found...:
In the thread, you'll find that the earliest reference (1999) came
from Mishy Lowe who said she posted the recipe to clayart "many moons
ago."
I hope that will be helpful to you.
Regards,
Maurice
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Pat wrote:
>Hi,
>My name is Pat and I am new to this list. I have a question about glazes
>and one in particular. I have read that all the glaze recipes should add
>up to 100 without the additions. I have two recipes for VAL'S TURQUOISE
>and they both only add up to 77/78 (see below). Am I safe in making this
>glaze, and could someone explain to me why some glazes don't add up?
Ron Roy on sat 8 sep 07
Hi Pat,
Good for you to post that extra information about the glaze - it would also
be important to include the cone drop and the kind of spar you used.
I do think there is something missing because of how the numbers are stated
- I tried adding in 22.49 EPK but that is not it - I have no idea what the
missing material might be - I checked Val Cushings book but no mention of
that glaze.
The alumina is low so I expect the glaze will deteriorate during washing -
you could do a couple of test tiles - leave one in the dish washer and
compare them now and then to see if it really a problem.
I tend to think it will also release copper into acidic food - you could
line a mug with it and leave it over night with orange juice in it to see
if you could taste the copper next day.
If you add at least 6 EPK to the glaze it will improve it considerably -
and will have some effect on the colour.
RR
>Hi,
>My name is Pat and I am new to this list. I have a question about glazes
>and one in particular. I have read that all the glaze recipes should add
>up to 100 without the additions. I have two recipes for VAL'S TURQUOISE
>and they both only add up to 77/78 (see below). Am I safe in making this
>glaze, and could someone explain to me why some glazes don't add up?
>
>VAL'S TURQUOISE (^5-9)
>
>Custer Feldspar 27.6
>Gerstley Borate 16.87
>Flint 21.32
>Whiting 8.82
>Dolomite 2.9
>Copper Carbonate 2.34
>Bentonite .8
>pale blue turquoise with a frost
>
>Val's Turq. cone 6, oxidation.
>
>Tested on mid range, iron flecked stoneware, fired to 1220c, oxidation.
>
>Receipe
>27.60 Custer spar
>16.90 Gerstely Borate
>21.30 Silica
>2.90 Dolomite
>8.80 whiting
>
>ADD
>0.8 Bentonite
>2.3 Copper carb.
>
>Subbed local spar for Custer
>All percentages rounded up to the nearest whole percent.
>
>Resulted in a stable, bright and clear, gloss turquoise glaze.
>Iron flecks came clearly though glaze. Slight, slight steaking and =
>pooling
>in bottom half of test bowl. Not a big color or covering difference =
>where double dipped.
>
>Same receipe with G.Borate subbed with Colemanite produced same results =
>as above
>Same receipe with G.Borate subbed with local frit produced same results =
>as above.
>
>Personal:
>A nice, smooth gloss with a good greenish turquoise color.=20
>Without the colorants, this makes a nice white gloss
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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