I am already known around here for my Iron Oxide [rust], well…how about Copper Oxide too. I am making [black] Copper (II) Oxide by first dissolving Copper (II) Sulfate penta Hydrate (CuSO4 * 5H20) crystals in water to form an aqueous Cu+2 solution. Then I take Sodium Hydroxide (NaOH) and add it to the Cu+2 solution. In some methods I have seen, you are then suppose to heat/boil the solution to turn the resulting Copper Hydroxide into Copper Oxide. By me adding solid NaOH to the water (carefully of course), I can skip this step because of all the heat generated into the dissolving and reacting process. So at this point, I have a thick, black suspension of Copper Oxide and a solution of Sodium Sulfate (Na2SO4). From here, I let the solution settle down and then decant/siphon off the water above it. I repeat this process several time, adding more water, decant it off, over and over until I am sufficiently satisfied that there is a negligible about of Sodium Sulfate remaining in solution. I then take the wet Cupper Oxide and pour it into an Aluminum baking pan and let it dry in the sun for several days until it is dry enough to crush it into a powder. I have done this procedure twice now and I have had a few problems I hoped you all could help solve. It seems to be very difficult to purify the solution of Sodium Sulfate, or some other impurity. As the Copper Oxide dries, a white powder forms along the edge of the container. I repeated my process of diluting and decanting (is there a technical name for that instead of my having to keep explaining what I do?) several times with large volumes of water and still it remains. I have also seen some type of impurity inside the dried Copper Oxide chunks, when I break them open, you can see it isn’t all CuO. My source of CuSO4 * 5H20 is from store bought root killer, advertised as 99% pure, 1% other. I don’t know what the “Other” is, but I would assume it is soluble and inert. Hopefully the company will respond to me email and let me know. I can only assume the white impurity is Na2SO4, or possibly something resulting from the other 1%. But whatever it is, I want to get rid of it. The Aluminum pan I use to dry the CuO seems to be a one time use only thing because as it dried, large holes were eaten away through the bottom and side of the pan. The Aluminum corroded and leaks water out the holes. I have noticed this with my Iron Oxide too, but it is quite obvious and much more drastic in my CuO batches. When I flipped the dried CuO chunks over, what do I find? Besides some of the white powder residue, I see that it is much more reddish brown than the black top is; the color is also on the bottom of the pan. When I saw this, it became obvious to me what happened; the Aluminum reduced the Copper (II) Oxide to Copper (I) Oxide. The Aluminum pan was oxidized, a lot, and that is what caused the holes in the pan. So now I was thinking about using a steel pan instead of Aluminum. This should work better I suppose, but it will still be Oxidized by the Copper somewhat (but I wonder if I can get away with it anyway?). I will either need to use a much less reactive metal as the pan, or perhaps use glass/Pyrex instead.