While I don’t believe CuO is a good finish for an incubator, it may work if not subjected to hot water or steam. Several alternatives, but I’d go with the hot oxide process mentioned first below.
A CuO finish is best produced by a hot, caustic oxidizing solution: 240
oF, caustic soda and sodium nitrate – Metal Finishing Guidebook, p. 382 (2003),online:
Proprietary solutions are normally used. This is more of a specialty service than is the hot black oxide finish on steels To locate a shop, try this ‘Jobshops’ link
If unsuccessful, go to EPI’s site
They have a suitable product:
“Ultra-Blak 420 for Copper/Brass — Oxidizing salt mixture for blackening copper, brass and bronze. Used at a concentration of 2 pounds per gallon of water at temperatures of 200° to 210° F to blacken copper surfaces with a deep black, abrasion resistant finish.”
Either use yourself or ask EPI for their nearest customer in your area.
Another, well-known product is ‘Ebonol C.’ It is/had been made by Enthone-OMI, but I couldn’t find on their site. Some ‘Ebonol C’ info is at
and
I looked at all 27 recipes for black/brown/gray finishes on Cu given in
The Colouring, Bronzing and Patination of Metals, R. Hughes and M. Rowe, Thames and Hudson (1991). 17 of these produce a sulfide, not an oxide. All 27 mention that a wax finish may or must be applied, surely not good for an incubator.
A number of art sites show a black copper finish which looks to be produced by heat, e.g.,
Finally, here is a less dangerous, Do-it-Yourself recipe for a blue-black finish:
“Copper carbonate, 1 pound
Ammonia, 1 quart
Water, 2.5 quarts
Temperature, 175
oF
The copper carbonate and the ammonia are thoroughly mixed before adding the water. An excess of copper must be present. The color, which is a blue-black, may be fixed by a subsequent dip in a 2.5% solution of caustic soda.”
--
Metal Finishing Guidebook (1998), p. 461.
Good luck, let us know the outcome.
Ken