gordon jones on sun 23 mar 03
help i'm a newbie and i messed it up, had a great glaze and used it with
nothing but success,ran out mixed it again and now it will not behave .i
bought a new batch of powders and think it may be in this area. got the
Mastering Cone 6 book and still trying to figure the math.
i am getting a lot of pinholes and have a new blue color.
should be a tan and green matte finish with a hint of blue
cone 6 whiting 24.18
custer feldspar 54.94
EPK 14.29
Flint 6.59
zinc oxide 9.89
cobalt oxide .50
copper carbonate 3.00
rutile 6.00
i think i was very careful in all meeasurments
any help would be greatly appreciated
could i substitute a frit based glaze for better results,
head hung low in winston salem
earthbound arts gordon
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Fraser Forsythe on mon 24 mar 03
Hi Gordon.
My guess is that you over did it with the cobalt.
Cobalt is a powerful flux. This may have lowered the
melting point of you glaze and caused it to boil
around the max temperature. If you cooled fast in the
middle of a boiling phase the bubbles would not 'heal'
over. Too much cobalt would obviously account for the
shift in colour to blue. Also since you were weighing
up a small amount the error margin will be magnified.
My advise is, before you compound your woes by
substituting with frits etc, make up another (smaller)
batch. That will tell you right off what you did. If
the second batch works you might want to double up a
base amount and add it to the first batch - thereby
diluting the over concentration of cobalt. It'll be
hit and miss.
If the second batch does the same thing you need to
isolate the materials you've just bought. The problem
could be a lot variation - and believe me there can be
big variations. Of course you could have miss weighed
one of the base amounts but that would not account for
the colour shift. Not so likely but possible is your
supplier sold you the wrong stuff. But please rule out
the obvious possibilities first.
This happens to everyone, and it can be very maddening
at times. Good luck.
Fraser
--- gordon jones wrote:
> help i'm a newbie and i messed it up, had a great
> glaze and used it with
> nothing but success,ran out mixed it again and now
> it will not behave .i
> bought a new batch of powders and think it may be in
> this area. got the
> Mastering Cone 6 book and still trying to figure the
> math.
> i am getting a lot of pinholes and have a new blue
> color.
> should be a tan and green matte finish with a hint
> of blue
> cone 6 whiting 24.18
> custer feldspar 54.94
> EPK 14.29
> Flint 6.59
>
>
> zinc oxide 9.89
> cobalt oxide .50
> copper carbonate 3.00
> rutile 6.00
> i think i was very careful in all meeasurments
> any help would be greatly appreciated
> could i substitute a frit based glaze for better
> results,
> head hung low in winston salem
> earthbound arts gordon
>
>
>
>
>
>
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> FREE*
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John Hesselberth on mon 24 mar 03
Hi Gordon,
I can only offer a guess on why your glaze shifted on you. First,
though, let me say that this is probably not a good glaze for
functional work. It has too little silica coupled with a fairly high
level of copper. The zinc may help rescue it a bit--I sometimes see
zinc-containing glazes that do better than I would predict. The glaze
should be matte and you say it is, so no problem there. The fact that
it is pinholing and is more blue (or purple maybe??) than the original
gives a couple hints. It is probably not melting as well and the
chemistry that affects color probably has shifted.
Was whiting one of your new ingredients? What did it say on the bag?
If you bought a little bag, call the supplier and ask them to give you
the information on the 50 lb. bag it came out of. The reason I am
suspicious is that I have had several hints recently that some
suppliers might be buying their "whiting" from the garden supply chain,
reasoning that "lime" (like we put on our lawns) is just ground
"limestone" which is calcium carbonate or whiting. And it is dirt
cheap if you get it at the garden store. Unfortunately, while that
material is sometimes whiting, it is often a low grade of dolomite
(containing calcium and magnesium instead of just calcium) instead of
whiting. That could explain the differences you seeing. Please
understand this is just a pure shot in the dark speculating on the
small amount of information you have given us.
However there are several other things it could be also. Please tell us
exactly which chemicals are "new" and what you know about them. Ask
your supplier for analysis sheets--tell him you are having trouble
reproducing a glaze and ask if he has any new suppliers. Then get back
and I or someone else will try to give you a firmer answer to your
problem.
Regards,
John
On Sunday, March 23, 2003, at 09:08 PM, gordon jones wrote:
> help i'm a newbie and i messed it up, had a great glaze and used it
> with
> nothing but success,ran out mixed it again and now it will not behave
> .i
> bought a new batch of powders and think it may be in this area. got the
> Mastering Cone 6 book and still trying to figure the math.
> i am getting a lot of pinholes and have a new blue color.
> should be a tan and green matte finish with a hint of blue
> cone 6 whiting 24.18
> custer feldspar 54.94
> EPK 14.29
> Flint 6.59
>
>
> zinc oxide 9.89
> cobalt oxide .50
> copper carbonate 3.00
> rutile 6.00
> i think i was very careful in all meeasurments
> any help would be greatly appreciated
> could i substitute a frit based glaze for better results,
> head hung low in winston salem
> earthbound arts gordon
>
http://www.frogpondpottery.com
http://www.masteringglazes.com
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