Bruce Girrell on thu 17 dec 98
Seasons' Greetings,
Last night I decided to try out a different glaze and used Tom Buck's raku
Red Lustre #8 as a starting point:
Gerstley borate 38
Frit F3134 31
Frit F3195 31
Copper oxide, red 10
Iron oxide, red 10
I have to admit that I'm still pretty new at this and this is the first time
that I've used _red_ copper oxide.
I placed all the ingredients in a sealed contained and mixed them, then
added water and mixed again - pretty much what I always do. When I opened
the container, though, I didn't find the slurry that I expected. Instead, a
red, dry powder covered everything. Since I've never seen this happen with
RIO, I assume that it is the red copper oxide. The powder is so non-wetting
that it remained dry even after sieving. The mixing container was completely
dry on the inside after pouring out the mess. Regardless of how I try to mix
this stuff, it will not go into suspension and simply stays on top as a dry
powder. Out of frustration, I added a wetting agent, Kodak Photoflo 200, and
that helped, but I still have a scum of dry powder this morning.
Question 1: What am I doing wrong? What is the proper way to do this?
Question 2: Do I pour/dip as is with the scum on top or skim it?
Question 3: Have I screwed anything up by adding the wetting agent?
Thanks to all.
Bruce "all wet" Girrell
Tom Buck on fri 18 dec 98
Bruce, perhaps I didn't mention that Copper Oxide Red is coated with a
"sealant" chemical to prevent oxidation of red to black while stored ...
this is for industrial users not us potters. So what I do when I place a
lot of Cu2O in a glaze recipe is: 1) Take most of the glaze water and add
a few drops of detergent (dishpan or clotheswasher) then add the Cu2O and
stir well; 2) Add the Cu2O slurry to the other ingredients and stir again;
and 3) Screen the glaze slurry (through a 60-80 mesh screen) and that will
ensure all the powders are reasonably well dispersed.
It's messy, I know, but such is the price one has to pay to employ
lots of copper and iron oxides in a Raku recipe.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East 43rd
St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of Ontario,
Canada).
Tom Wirt on sat 19 dec 98
-----Original Message-----
Subject: Re: Wetting glaze ingredients
----------------------------Original message----------------------------
>Bruce, perhaps I didn't mention that Copper Oxide Red is coated >with a
>"sealant" chemical to prevent oxidation of red to black while stored
Tom....does this imply that once mixed up, the CU2O has a shelf life because the
coating is now washed off?
Tom Wirt
claypot@hutchtel.net
doug honthaas on sat 19 dec 98
Do the instructions of wetting copper oxice in water and detergent to help
disolving problems apply to copper carb? Thanks. Veronica
Tom Buck on sun 20 dec 98
Tom W:
You ask what happens to Cu2O (copper oxide red) once the
protective coating is removed by dishpan detergent (or other surface
active agent). Cu2O will slowly become CuO (black) if the powder has
access to oxygen in the air at room temperature. Should this occur during
storage, then the molecular weight gets changed. In pottery, since we work
to say 0.5% accuracy, we can afford to use blackish red copper oxide and
not worry about the results (we will still get greens, or blues, or reds).
But in an industry where more precision is required, a modest change in MW
would likely be most troublsome.
As for removing the coating as the glaze mix is being prepared,
well since the glaze water keeps the oxygen away (O2 is only slightly
soluble in water), once the glaze recipe is fully mixed and screened
there would be slight chance that the Cu2O would change to CuO at room
temperature, and even if it did it would not matter since you have
already weighed out the right amount of red oxide that the recipe calls
for. [100 g red = 111 g black = 154.5 g carbonate basic = 175 g copper
sulfate decahydrate].
When the glazed pot is fired to temperature/cone, as the
temperature goes beyond 1000 oC all copper compounds become CuO (black
oxide) in an oxidation firing. If heavy reducing occurs below 1000 oC and
above then Cu2O will become/stay dominant, with some Cu metal also being
formed.
Good pots. Happy Holidays. Tom B.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of
Ontario, Canada).
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