The art of glass shewing how to make all sorts of glass, crystal and enamel : likewise the making of pearls, precious stones, china and looking-glasses : to which is added, the method of painting on glass and enameling : also how to extract the colours from minerals, metals, herbs and flowers ... : illustrated with proper sculptures / written originally in French, by Mr. H. Blancourt, and now first translated into English ; with an appendix, containing exact instructions for making glass-eyes of all colours.

CHAP. LVIII. A way to make a fair Chalcedony in Glass.

ALtho Chalcedony is not so dear as it has been heretofore, since it is found in Europe; yet Peo∣ple have not left off counterfeiting it by help of Art, to make several Works of it no less beautiful than the true, and much cheaper.

We will shew three different ways to prepare this Chalcedony, which will make three different Species of it, all of them very fair, but whose Beauty may be also augmented by the number of Ingredients we compose them of, and which cause those Diversities of Colours, which that Stone ought to have.

Among the rest of the Ingredients we employ in this Subject, there are some that give no colour to Glass, as Tartar, Soot, Sal-Armoniac and Mercury.

Those that are of an unctuous Nature, as Lead, Soot, Tartar, the Azure-stone often hinder the Union of the Ingredients, by reason of the Separation which may happen by the cooling the Metal; which does not happen to those who know how to observe the degree of heat, wherein the principal knowledge of this Art consists.

To make the first sort of Chalcedony: Put two Pound of Aqua fortis (whereof we have given the Prepara∣tion in Chap. 52.) into a Glass Body with a long Neck, four Ounces of fine Silver in small and thin Plates, or granulated, put the Body in an Ash Furnace over a soft Fire, or in warm Water, and the Silver will be presently dissolv'd. At the same time take ano∣ther Body and dissolve in it 6 Ounces of Quick-silver in a Pound and half of the same Aqua fortis. After that pour both the Solutions together into a greater Body, which put in the same Bath, or warm Water, or Ash-Furnace: then add to it six Ounces of Sal∣Armoniac, which dissolve over a gentle Fire; then put to it one Ounce of Zaffer, and half an Ounce of Manganese prepared, little by little, with as much Ferretto of Spain also little by little, for fear the Matter coming to swell too much should break the Vessel. Add to all these Ingredients one Ounce of Crocus Martis calcined with Sulphur; as much Scales of Copper thrice calcined, which ought to boil like Manganese; as much blue Lake that the Painters use; and the same quantity of Red Lead, the whole reduc'd into Powder. In putting in these Powders you must gently stir the Glass Body, that they may the better incorporate with the Aqua fortis, never∣theless take care there be not too much heat; then you must well stop the Matras (or Glass Body) stir∣ring it well every Day for ten Days, that the Pow∣ders may well incorporate, and that they may always appear as separated from the Water. After that

put the great Glass Body in a Sand-Furnace in a temperate heat, or rather empty it into a GlassCucur∣bit, after having luted it at the bottom, and put it over the same Fire, so that the Aqua fortis may eva∣porate in 24 Hours, and at bottom of the Vessel you will have a yellow Powder, which keep safely in Glasses for use. When you are to make Chalcedony, take white Crystal in Glass, well purified, and that has been often melted; for Crystal new made is not fit for that Operation, because the Colours will not stick to it, but are consumed by the Frit. Put about twenty Pound of this sort of Crystalline Glass into a Pot; and being well melted, put in about three Ounces of your Yellow Powder at three different times, mix the Glass well with it each time, that the Powder may incorporate with it, the Glass being thus well mixed, let it stand an Hour, then mix it once more and let it stand during 24 Hours: Then mix it again for the last time, and make an Essay of it, it will give a yellowish Azure colour. Having made your Essay, and found your Matter right, you may take your Pot out of the Furnace, and when it is cold you'll have colours which shall represent Wavings of the Sea, and other fine things. But to have a very fair Chalcedony, you must make a second Ope∣ration to join to the first, by taking eight Ounces of Tartar calcined, as we have shewn Chap. 41. Two Ounces of Soot of the Chimney well purified, half an Ounce of Crocus Martis calcined with Sulphur: Mix the whole well together, then put it into the melted Metal at five or six different times; otherwise the Impetuous Swelling of the Materials would break the Pot, and the whole would be lost; which may be avoided by putting it in little by little, stirring it each time well, that the Matters may incorporate: Make the Pot also boil, then let it stand twenty four Hours. After which you may work it into what you

please, which put in the Furnace to whiten, and see if the Glass please you; if it be green without, and blue, white, red, yellow and of other Colours like Jasper and Oriental Agat. If looking on it obliquely it be red like Fire, and held to the Sun it shew the Colours of the Rain-bow by reflection of the Rays; if so, then it is fit to make all sorts of Vessels which may be polished at the Wheel. If it be pale and clear, you must add to it more calcined Tartar and Soot as before, stirring it well to make it incorpo∣rate; then let the Glass stand and purifie several Hours, and afterwards work it as you please.

Chalcedony is much used for the Effigies of Kings and Princes, for Heads, Cups, and many other Vessels; principally for making Seals, because it may be gra∣ved easily, and the Wax will not stick to it.