Note 331 — COLOURED GLASS.—ARTIFICIAL GEMS.
William Johnston translation
In what the art of Abraham Helmback, a Nuremberg artist, consisted, I do not know. Doppelmayer, in his Account of the Mathematicians and Artists of Nuremberg, printed in 1730, says that he fortunately revived, in 1717, according to experiments made in a glass-house, the old red glass; the proper method of preparing which had been long lost.