Hand machined mechanical pencils

Making cuprous oxide (01/02/12)

I came across this paper which describes making grainless fluorescent screens for detecting electron beams. I thought it might be nice to try, but I needed some cuprous oxide. Lacking any, I made some from Fehling's solution. It turned out that the screens weren't fluorescent (at least to UV), but making the cuprous oxide was rather nice.

Fehling's 1 is 7g of copper(II)sulphate in 100mL water. Fehling's 2 is 35g of potassium sodium tartrate (Rochelle salts) and 10g of sodium hydroxide in 100mL water. When mixed, they produce the deep blue colour of the copper complex. Upon adding a teaspoon of glucose and heating, the solution turns murky green, then finally bright opaque orange as the cuprous oxide is formed. All that remains is to filter the solution and dry the resulting precipitate.

I tried painting some of the oxide on to glass and firing it at 350°C for 30mins. Unsurprisingly, I ended up with black cupric oxide. The glass didn't appear to fluorescent under UV - maybe it only responds to electrons.

Solution 1 on right, solution 2 on left (sorry about the ordering)


Glucose added, precipitate beginning to form

Precipitate fully formed

Filtered cuprous oxide

Painted on to some soda-lime glass

After firing in the kiln