Magic Mirrors - Page 3
Brewster, being an expert in the polarisation of light, first of all suggests that might be the answer. "It is well known that silver polished by hammering acts differently upon light from silver that has received a specular polish." Then he suggests that the reflected image was not an image of the figures on the back of the mirror but a deliberate deception. The figures are a copy of the picture which the artist has drawn on the face of the mirror and then concealed by polishing. Brewster also proposes that the figure may be eaten out by a dilute acid, so as to remove the smallest possible portion of the metal. The surface can then be polished with a cloth so that the sunken parts will be as highly polished as the rest. He finally recommends that magic mirror might "furnish a lucrative article of trade"In 1875 Dr. Geerts published a paper in the Transactions of the Asiatic society of Japan where he described in some detail how the magic mirrors were cast. He gave the metal mixture for the best mirrors made in Kyoto as :-
After the mirrors have been well polished they are covered with a layer of mercury amalgam. " The amalgam is rubbed vigorously with a piece of soft leather, which manipulation must continue for a long time until the excess of mercury is expelled and the mirror has got a bright, reflecting surface."
On 24th May 1877 Professor R.W. Atkinson of Tokyo University published a letter in Nature describing a magic mirror he had been shown by a friend. "Considering the mode of manufacture I was led to suppose that the pressure to which the mirror was subjected during polishing, and which is greatest on the parts in relief, was conserved in the production of the figures. On putting this to the test by rubbing the back of the mirror with a blunt pointed instrument, and permitting the rays of the sun to be reflected from the front surface, a bright line appeared in the image corresponding to the position of the rubbed part. This experiment is quite easy to repeat, a scratch with a knife or with any other hard body is sufficient. It would seem as if the pressure upon the back during the polishing caused some change in the reflecting surface corresponding to the raised parts whereby the amount of the light reflected was greater; or supposing that of the light which falls upon the surface, a part is absorbed and the rest is reflected, those parts corresponding to the raised portions on the back are altered by the pressure in such a way that less is absorbed, and therefore a bright image appears."