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ON IRIDESCENT SILVER. 
ART. IX.— NOTE ON IRIDESCENT SILVER. 
By Prof. John Brockelsby. 
It is well known to those who are conversant with optical 
phenomena, that the brilliant play of prismatic colours ex- 
hibited by mother of pearl is due to the structure of the sur- 
face ; provided the shell is cut and polished in a particular 
manner. This interesting fact was announced to the scientific 
world in 1829 by the discoverer, Dr. Brewster, who success- 
fully transferred by pressure the splendid tints of the pearl to 
black wax, fusible metal, balsam of tolu, lead, tin, and various 
other substances. The colors displayed by fusible metal pos- 
sess at first extraordinary beauty, which in a short time is 
partially lost, owing to a change that occurs upon the surface 
of the metal. 
A few months ago, while engaged upon some experiments 
in electrotyping, I was led to think that by this process the 
hues of the pearl might be readily transferred to those metals, 
which from their hardness are incapable of receiving impressions 
in mass, but yet, on account of their freedom from oxidation, 
retain for a long time a surface comparatively pure. I there- 
fore took a Smee's battery, which I had just constructed, and 
after several experiments succeeded in obtaining small sheets 
of silver, radiant with the hues of the shell. When seen by a 
single light, as that of a lamp, the play of colours is surpass- 
ingly beautiful, scarcely inferior to that of the pearl; and 
where equal care was employed, the plate of silver, which was 
formed eight months ago, rivals in brilliancy that which came 
fresh from the battery a few hours since. 
The process by which this result is obtained is as follows. 
The first thing required is to prepare the shell. This is ef- 
fected by grinding, and polishing it upon the back, in such a 
manner as to cut through the numerous concentric strata that 
compose its substance. When this is done, by the aid of a 
