red copper/black copper

[Mark Armstrong]

I did a little searching but did not find a specific answer about being able to substitute black copper for red copper. My local pottery supply places no longer carry red copper only black.
Can black be substituted for red? The molecular weight of red is 1.8 times greater than black, does that mean I need to increase the amount of black copper by 1.8 to achieve the same transparent copper blue colour. Thanks for the help.

[Steven O'Day]

I don't know about in glass but in ceramic glazes it depends on the desired color. Red copper will make a reduction red easier than black, it is the reduced form of black copper. Red fired in oxidation will generally go blue or green.
The molecular weight is not as straight forward as it seems, there is a good discussion here

[Pete VanderLaan]

Red Copper- Cu20

Black Copper- CuO

So red has more oxygen than black. It is easier reduced and will take form as CuO. That extra Oxygen is why it weighs more. I use Red copper in all my copper rubies. I've used the carbonate as well but you're paying for carbon you'll not use.

[Josh Bernbaum]

US Pigment say on their site that they will ship to Canada.

https://uspigment.com/product/copper-oxide-red/

[Mark Armstrong]

Thanks for the answers. I have ordered from U.S. pigment before and had good luck. I would just like to find something more local with shipping rates and dollar exchange.
Here is where my brain gets confused, I understand from Petes colour class,for the copper rubies I would want a reduced glass, less oxygen, but does it make a big difference for the transparent blues.
Would copper carbonate be better than the black copper?
Thanks for the link Steven, I don't really have any chemistry background, so its all foreign to me.

[Pete VanderLaan]

I would just use your regular clear glass to make copper blues. In general United Pigment is rather expensive. If you use the carbonate, you are paying for oxygen and carbon (CO2) as opposed to the Cu0. It is worth pointing out that the carbonates can be perceived of as being "softer" on going into solution. I find that true of Cobalt Carb as well. I can't explain that better. you have to do it.
Copper bears watching as it makes expansions and viscosities fairly crazy.

[Mark Armstrong]

Thanks Pete,
I have been making a copper blue using spruce pine TS and Everclear and been very happy with it. I have really noticed the viscosity, it fines out beautifully. I was more curious about, best, if any substitute for the red copper, for what is available locally. It sounds like the copper carbonate might be the way to go.
Local large pottery supply houses in Canada offer black copper oxide at roughly $44 per 500grams, or just over a pound. Even with exchange US pigment seems like a good deal. Are there less expensive places you can point me towards? I just got a quote on Potash, a 55lb bag is now $166.

[James Burts]

Originally Posted by Pete VanderLaan

.....In general United Pigment is rather expensive. .......

Who would you recommend purchasing from these days? Looking to acquire a number of things, and always looking for the best sources.

Thanks.

--James--

[Pete VanderLaan]

Originally Posted by Mark Armstrong

Thanks Pete,
I have been making a copper blue using spruce pine TS and Everclear and been very happy with it. I have really noticed the viscosity, it fines out beautifully. I was more curious about, best, if any substitute for the red copper, for what is available locally. It sounds like the copper carbonate might be the way to go.
Local large pottery supply houses in Canada offer black copper oxide at roughly $44 per 500grams, or just over a pound. Even with exchange US pigment seems like a good deal. Are there less expensive places you can point me towards? I just got a quote on Potash, a 55lb bag is now $166.

*****
Sadly, expect the potash to go up. It's being used to make fertilizer of which there is a great shortage in Ukraine, the world breadbasket. It may come down again but most stuff never does. I think my last quote for K2Co3 was more like $200. I'll check.
Sourcing suppliers has been really difficult since I wrote the stuff for Glassnotes. You can see if Ceramic Color and Chemical, or Standard Ceramic supply still exist. Those are options. 45 bucks a lb sounds awful. The carb will be worse. Just look up red copper on the web and see what pops up. I usually get at least 10lbs when I order such stuff and the price improves.

[Pete VanderLaan]

Standard Ceramic- Pittsburgh had copper carbonate at $8.50 lb when I googled it. I did not find the red copper but I didn't try very hard either. I suggest you check there. If I had to choose between what you are getting screwed for and this stuff, I'd use the carbonate.

I just straight up googled black copper and I saw one place at $14.00 lb. I saw your fifty five dollar guys too.

[Mark Armstrong]

Thanks for the lead Pete. It`s looking like my Canadian Potash is not such a bad deal. It went up from $110 a 55lb last year.

[Pete VanderLaan]

Well, I screwed that up and realized it driving to town. My potash is now $2.00 lb. That's up 68 cents from last year. I don't expect it to go up more any time soon though.

[Hugh Jenkins]

I have not seen a more misleading chemical conversation here. CuO is the Cu+2 form of copper (black or cupric Oxide). Cu2O is the +1 form of copper (red or cuprous oxide). The Cu2O supplies more copper per molecule at a higher molecular weight but is the more efficient way to put copper into a glass or glaze formula by weight. It is also the least oxidized, meaning the lower positive valence of copper, so it make sense that it would reduce more easily. Copper carbonate carries a CO3 -2 component which makes it a less efficient copper additive but way easier to melt with its weaker bond to the carbonate.

I have experienced the difference in the melting and the heating of copper glasses. In the range of .25 to .5% it is a very soft working glass that can take over the heat behavior of mixed color creations. What somewhat baffles me is that copper is easy to melt in but often has lead in its formulas which is really unneeded until much higher percentages.

[Pete VanderLaan]

I did not mean to mislead. You are certainly correct. I am interested in the prices of the different materials and when you are or aren't paying for oxygen or carbon. Actually I appreciate your observations a lot. The places to buy the materials are good.

[Mark Armstrong]

Thanks everyone for the discussion on this. I did check into Standard ceramics, thanks Pete. It seems at the moment they do not have red copper, but do carry black. The per pound price is actually slightly higher than US pigment. They will ship to Canada.
Ultimately my next question is whether I am doing my math correctly for replacement quantities. I understand ( I am pretty sure) the link from Steven and it was very helpfully. Following that info, I have calculated that I would need 1.73 times as much Copper Carbonate compared to Red Copper. Places on the internet suggest that red and black copper are interchangeable weight wise. Suggesting that a substitution of 1.5 times as much Copper Carbonate. Could someone kindly confirm I am doing my calculations correctly. Thanks,
Happy November!!

[Pete VanderLaan]

well, just go to the periodic table and do the atomic weights of the copper, the oxygen and the carbon.

My caution would be that copper is strange stuff in a melt and makes glasses inexplicably runny. It also can dramatically change the expansion factors as well as the viscosity. I tend to start low and go up.
I haven't used black copper in 30 years since the red has worked so well for me. That's true of the carbonate as well. We never used it in the color rod work either.
I think Seattle Pottery would be another source. They're usually pricey.