Harper's new monthly magazine, 41 / 1870
The use of mica in spectacles, for protecting the eyes of workment from the heat and glare of the fire, is rapidly coming into general favor; and complete masks, and even cylinders entirely encincling the head, are sometimes used for a similar purpose when a greater safeguard is required. Experiments have been lately made in regard to the manufacture of blue spectacles from this material. The best method of accomplishing this has been found to consist in the use of plates of transparent blue gelatine fixed between two layers of mica, thus protected from the action of the heat. The experiment of applying the blue coloring matter directrly to the surface of the mica itself failed in consequence of the impossibility of forming a suitable combination; but the gelatine layer, as indicated, answers all the purposes desired.