Blue colour on copper plates
My vote on this (and I did see the plates) is that it was most probably an
very thin oxide layer. The colour of these depends on thickness.
Hydrated copper(II) compounds have only a pale blue colour and could not
account for the density, although of course ammonia forms much more
intensely coloured complexes with copper(II).
Peter Marshall
On Fixing Shadows, Dragonfire and elsewhere:
http://faraday.clas.virginia.edu/~ds8s/
Family Pictures & Gay Pride: http://www.dragonfire.net/~gallery/
And on: http://wwwspeltlib.demon.co.uk/