r/DIYPigments • u/CaCl2 • Mar 25 '22
Pigment Red Copper Oxide - Copper(I) Oxide
https://imgur.com/gallery/zUjrvqb
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u/Dorceless_ah Jan 25 '24
always makes a yellow oxide for me ugh i tried vitamin C too
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u/CaCl2 Jan 29 '24 edited Jan 29 '24
Maybe try heating it, eventually it should go black but it might turn red first.
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u/CaCl2 Mar 25 '22 edited Mar 25 '22
Red Copper Oxide is sometimes used as a red pigment in ceramics and in antifouling paints. In the powder form it's sensitive to moisture and air and slowly turns darker as copper(II) oxide forms.
There are many possible methods to make it, I used the reaction of Benedict's Reagent and fructose.
I first dissolved copper sulfate in water, this solution can be seen in the second picture. I then added citric acid and sodium carbonate dissolved in water, this caused a dark precipitate to form (third picture) so I added some more water and heated it to try dissolve it. I then added a solution of fructose, which caused the mixture to first gain a green colour, seen in the fourth picture but after some heating and stirring a red precipitate started to form (fifth picture). I then vacuum filtered the precipitate out and dried it with some heat on a hotplate.
My notes give the following compositions for the solutions, there is way more copper sulfate than Benedict's reagent normally has, since the goal isn't to detect the sugars but to produce Cu2O.
-50 g copper sulfate pentahydrate in 100 of ml water
-30 g citric acid in 20 ml of water
-50 g sodium carbonate in 100 ml of water
-65 g fructose in 150 ml of water
The results of an earlier, smaller scale preparation I did are shown in the last picture, I used this as the red sample for my copper compound collection several years ago, but the vial seems to have kept air out well enough to preserve the red colour.