Chemical Forums

Specialty Chemistry Forums => Citizen Chemist => Topic started by: Arcaeca on August 17, 2019, 01:59:13 AM

Title: Trying to make red copper & iron oxides
Post by: Arcaeca on August 17, 2019, 01:59:13 AM
So in my continuing quest to make pigment from scratch, I want to make a red pigment, and it seems like iron(III) oxide and copper(I) oxide are probably my best bets, since iron and copper metal are more easily available and less absurdly toxic than, say, arsenic (in realgar, As4S4) or mercury (in vermillion, HgS). However, I've not had much success in making the red oxide of either metal. Trying to make iron(III) oxide by oxidizing iron metal in hydrogen peroxide, the oxide layer formed is more reddish-brown than the vibrant red that's supposedly achievable, and copper(I) oxide can supposedly be made by heating copper metal red-hot in air, but I only end up forming a layer of black copper(II) oxide on the outside (which is still good as black pigment, but not what I'm after).

Most tutorials I've seen for making copper(I) oxide are essentially Benedict's test, or a modified version of it; the problem is they all start with copper(II) sulfate, which I could make if I had sulfuric acid in which to dissolve my copper. Sulfuric acid drain openers are readily available but almost always come with an anti-corrosive agent, which completely defeats the point, since corroding the copper is exactly what I want it to do.

And the tutorials for making iron(III) oxide I've seen usually use electrolysis, but I don't have a power source I can use (like a spare car battery?) and don't know what to use as electrodes. And the color of the resulting oxide still usually seems... questionable.

Given my limited toolset, what procedure will give me the most vibrant red from copper or iron?
Title: Re: Trying to make red copper & iron oxides
Post by: nathanwind on September 24, 2019, 09:43:17 PM
Hi. I cant help you with pigments but I know that you donĀ“t need much current to make electrolysis by experience.

With a regular cellphone charger, usually 500mA, is usually too much current for small samples.

I made a current regulator with a 317 transistor and a resistor to cut voltage from 5v to 2.5v and 500mA to 100mA.

For iron electrolysis you need iron electrodes/anodes and for copper, copper electrodes/anodes.

Hope this helps. Sorry for my english.