Peet Robison on tue 2 dec 97
Karl wrote a very intereting post, imo, and it should open up an
educational dialog on the elusive copper red glass.(glaze)
What follows is my non-scientific view on the subject after more than 20
years of experience melting glass, including Cu rubies.
From what I have learned, it is very important to have Zinc and Potash in
the glass. I don't know why for sure, but it could be that they help the
metals go into a complete solution. Another thing I have learned is that
by using REDUCED tin (black tin oxide) and REDUCED copper(red copper
oxide)your chances of success are greatly increased.
We don't melt the glass in a reducing atmosphere. Period. The glass goes
red in the striking stage while being worked, near the end of the piece and
sometimes it strikes in the annealing oven. In a kiln firing that would
mean you want to hold the ware around 1200 F for the "strike". It would
probably take 20 minutes or more. Watch carefully! If it strikes too long
you will have mud, the dreaded liver color or even black.
Why don't I reduce the furnace while melting? Again I am not sure but I
feel it is because the glass composition itself is "reduced", trying to
strip Oxygen from the Cu. If I try to melt Cu red using a batch that
contains excess O2 in the form of Niter it won't work. However if I take
the scrap (cullet), crush it and mix in Cu, Sn, and Zn it mkes a near black
Cu red! The O2 has been taken out after the initial melt.
The wt %:
Red copper oxide , no more than 1%, usually .5%
Black tin, 1%
Zinc, 1%
For Black Tin Oxide, try Goldschmidt Industrial Chemical 1-800-426-7273
(no affiliation)
Peet in cloudy and cold Santa Fe
Peet Robison on sun 14 dec 97
Karl wrote:
>The title of this thread is ridiculous. Cu red is impossible in
> oxidation.
Karl, I hope you mean that it is impossible to make a red with oxidized
copper. I would agree. But if you are saying it is impossible to make a red
in a neutral or even oxidizing *atmosphere* then I strongly disagree! We do
it all the time in a small pot furnace. The glass composition is reduced,
not the atmosphere.
Peet, in chilly but sunny Santa Fe
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