Dictionarium polygraphicum. To give glass the colour of lapis lazuli.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
Lapis Lazuli, which is a fine blue, and full of veins of gold, will not be easy to imitate, without a great deal of care and industry in its preparation.

To make this fine colour, you must use the same matter as for the fine white; and when it is in fusion in the pot, you must add to it by little and little, the blue enamel in powder, which is made use of by painters, mixing the whole well together each time, and that as often as there is occasion to make this colour.

Then try it, whether the colour is to your mind, and when it is, let it stand for full two hours, and make a second essay of it; if the colour be perfect, let it stand ten hours, and then mix it again.

If it keeps in the same estate without changing the colour, you may employ it in making what vessels you please, which will be of the true colour of Lapis Lazuli.

If in working this glass it hapens to rise, you may cast in a little leaf gold, which will make the glass approach yet nearer to Lapis Lazuli, and which will in a moment stop the rising of the metal, as sugar will do in boiling oil.

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