Copper forms two oxides, the suboxide and the protoxide; the suboxide colours glass red, while the protoxide renders it green.
If there is much sugar, the first drop will throw down a yellow precipitate of suboxide of copper, which becomes rapidly red.
Hence it is easy to calculate the total amount of copper which has been present as suboxide.
This color was quite superficial, and the glass itself was opaque and of a vermilion tint, attributed to suboxide of copper.
The suboxide of a grayish blue colour, which forms a kind of crust upon a plate of lead long exposed to the air.
This specimen is interesting, as showing the early use and knowledge of suboxide of copper as a stain or coloring agent for glass.