The great objections to mirrors coated with pure silver are the yellow character of the reflected light, and the fact that such mirrors are apt to be affected by sulphur. M. Lenoir has invented a process which is said to avoid these difficulties. The glass is first silvered by means of tartaric acid and ammoniacal nitrate of silver, or by the process described in the preceding section, and is then exposed to the action of a weak solution of double cyanide of mercury and potassium. When the mercurial solution has spread uniformly over the surface, fine zinc dust is powdered over it, which promptly reduces the quicksilver.

And permits it to form a white and brilliant silver amalgam, adhering strongly to the glass, and which is affirmed to be free from the yellowish tint of ordinary silvered glass, and not easily affected by sulphurous emanations.