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Gold coloured Glass, with metallic subjlances.

Precipitates of silver,baked on glass, stain it yellow,and likewise give a yellow colour on being mixed andmelted with forty or fifty times their weight of vitreouscompositions : the precipitate from aquafortis by fixt al-cali seems to answer best. I have likewise obtained yel-low glasses with certain preparations of iron, particularlywith Prussian blue. But neither with silver nor with irondoes the colour succeed constantly, or approach to thehigh yellow of gold.

The nearest imitations I have obtained of the colour ofgold in glass, were produced with antimony and lead. Aquantity of crude antimony in fine powder was calcined bya little at a time in a flat iron pan, with care to prevent asmuch as possible its running into lumps, by using a verygradual fire, and keeping it constantly stirring, till at length,when brought to a full red heat, it neither softened noremitted any fumes. The ash coloured calx, weighinglittle more than half of the crude antimony, was put into acrucible, and urged with a strong fire in a blast furnace: itmelted into a glass, dark coloured and opake in pieces of anyconsiderable thickness, and of a transparent yellow whendrawn out thin.

Some of this glass, reduced to powder, was mixed andmelted with four times, three times, and twice its weightof powdered flint glass: the glass resulting from the firstmixture was of a transparent pale yellow, from the seconddeeper, and from the third of a pretty deep yellow, with-out any mixture of greenish or brown. Equal parts ofthe glass of antimony, of flint calcined and powdered, andof minium, formed a glass of a high yellow, and with twoparts of glass of antimony, two of minium, and three ofpowdered flint, the colour approached still more to that of

gold.

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