Acetic acid and ammonium complexes (including horse urine) leave a green 
patina. If you want a black one, H2S is used. Degrease the object and 
put it in a hermetic container OUTDOORS. Put a flask containing a little 
iron sulphide in the container and add some dilute hydrochloric acid and 
shut the container FAST. Leave for as long as it takes and carefully 
open a tiny corner of the container to allow the H2S to dissipate slowly 
(it is toxic to plants, animals and you: if you can more than just smell 
rotten eggs, then you and your environment are being poisoned: spraying 
in cold water will help slow down the dissipation of the gas and won't 
dissolve the patina.)

Brian

Jack Olson wrote:
> Does anyone know how to make copper tarnish FASTER?
> 
> (I want to make a wire sculpture look older)
> 
> Saturday project.... Jack
> 
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