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. CCXXXV. To Extract the Ultra-marine.

NOW we come to take out the Vltra-marine, from its Confinement to make it appear Tri∣umphant, and in its full Glory.

Take therefore the Loaf of Cement and Powder, washing it in the same Water extraordinary well with your Hands; weigh it to know the quantity of Oyl it requires, and put it into an Earthen-Bowl, or Dish, very smoothly glazed, rubbing first the Bot∣tom with your Linseed-Oyl; then pour in Water scarce warmed, until it arise two Inches above the Matter; let it stand in this condition a full quarter of an Hour (or less in the Spring-time;) pour this Water afterwards into the Vessel mentioned Chap. 230. adding more warm Water to your Matter, and so 'twill soften: Continue thus whilst there remains any Tincture thereon; by this means all the substance that is good for any thing, will be separated from the Cement, which cannot be done otherwise.

Whilst it is imbibed in the warm Water, you must move and roul it gently round with two Sticks, or Spatula's of Box, or any other well polished Wood rounded at the ends smooth like a Wallnut; let them be about an Ell long, and an Inch thick. Whenever you perceive the Matter stick to the bottom of your

Dish, rub your Hands with Linseed-Oyl, and stir it about leisurely so as to colour the Water, which you must put along with the former, in the mean time holding up the Matter with your Staves, lest it should stick to the Vessel.

Take notice that a little steeping at first will tinge the Water very much, and when the Cement is just yielding its colour, it will discover certain Bluish Streaks on the Water, like the Sun-Rays, and then you must strain this Water out among the other, through a Scarce, that the grosser part of the Ce∣ment may remain; afterwards pour in by little and little the fresh warm Water, stirring the Cement easily, that it may not dilate too much, and give its colour all at once. After you have thus stir'd it a∣bout five or six times, close and amass it anew, by which means you'll see how much 'tis diminished, and what quantity of colour it has given.

If the Lapis be good and right, you'll find it will the first Steepings yield about four or five Ounces of Vltra-marine, which keep apart by its self as the best and finest colour, tho it appear grosser than the others of this sort, by reason of the Gold-coloured Veins, which are peculiarly therein.

For the second, whereof you'll have three or four Ounces, you must follow the Processes aforemen∣tioned, this indeed will be finer than the o∣ther, but not so good a Colour; keep it also by it self.

Draw off a third, and this will be still siner than the former, but paler and more bright co∣loured. You must still pursue the same Directions to extract it, letting your Water be but half luke∣warm, and take care to manage the Cement dex∣trously with the Spatula's, and so preserve the Co∣lour apart.

You may extract a fourth Colour after this rate, but the Water must be hotter, and you must press the Cement very well with the Spatula's to squeeze out the Colour, and if meer Water will not do, make use of the mild Lixivium of Chap. 229. this last Colour will be Grayish, or Ash-colour'd, and of no great value, and therefore not at all to be mixt with any of the rest.

Observe here that you can't take up less than eight Hours full, to extract the Colours, nor than ten or twelve to allow the Water for setling, and if you perceive the Colour does not come out free e∣nough with the warm Water, add a third part of our mild Lixivium, and if that does not do, use all Lixivium, but let it be cold, and when that fails too of effecting it sufficiently, you must make a Lixi∣vium of Vine-stalk Ashes, and this being strained, let it boil for half a quarter of an Hour, until it be sharp enough to bite your Tongue; and then let it settle and grow clear; this is your last shift for extracting your Colour, and with this heated, wash your Cement very well, and set it aside: The whole design of all this trouble, is only to serve for obtaining the greater quantity of Vltra-ma∣rine, and this consists in the goodness of the La∣pis Lazuli and the Cement, which the Circumspecti∣on and care taken in all their Preparations must advance.