Dictionarium Polygraphicum. Allum, Alum. Allum Water, Alum Water.

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.
Allum, Alum is a principal ingredient in colouring and dying; neither of which in many cases can be well perform'd without it.

It is a kind of mineral salt of an acid taste, leaving in the mouth a sense of sweetness, with a considerable degree of astringency.

Allum is either native or sactitious, the natural is found in the island of Milo, being a kind of whitish stone very light, friable and porous, and streak'd with filaments resembling silver.

Factitious Allum is made after different manners, according to the different materials whereof it is made.

Allum is of divers sorts, red, Roman, plumose, saccharine and burnt, the three last of which are not proper native Allums.

Allum is principally produc’d in England, Italy and Flanders.

The English Allum call'd also Roche Allum, is made from a bluish mineral stone found plentifully in the hills of Yorkshire and Lancashire.

The stone they calcine on a hearth or kiln, and steep it successively in several pits of water; and then boil it for about twenty four hours: lastly, letting it stand for about two hours, the impurities subside and leave a pure liquor; which being remov’d into a cooler, and some urine added to it, begins in three or sour days to gather into a mass; which being taken out, wash’d and melted over again, is fit for use.

In the Allum works at Civita Vecchia, the process is as follows: The stone, which is of a ruddy hue, being calcin'd, they boil and dissolve the calx in water; which imbibing the salt, i. e. the Allum, separates itself from the useless earth. Lastly, leaving the water thus impregnated with salt to stand some time, it crystallizes of itself, like tartar, about a butt, and makes what they call Roche or Roman Allum.

The Swedish Allum is made of a mineral which contains a great deal of sulphur and vitriol, not to be taken away; but by calcination or distislation.

The matter remaining in the iron vessels, us'd in separat ing the sulphur from the mineral, being expos'd to the air for some time, becomes a kind of bluish ashes, which they lixiviate, crystallize and convert into Allum.

Allum in colouring and dying, serves to bind the colour upon the stuffs, and has the same use there, that gum water and glutinous oils have in painting; it likewise disposes stuffs to take colour, and adds a degree of briskness and elegancy to them, as is seen visibly in cochineal and the grain of scarlet. It also preserves paper, that has been dy’d in its water, from sinking when wrote upon.

ALLUM WATER, ALUM WATER, boil four ounces of Allum in a quart of rain or river water, till the Allum is dissolv’d and let it stand twenty four hours.

With this water wash prints you design to colour, and it will fix the paper so, that the colours will not sink or run in it, when you lay them on, and will help likewise to brighten your colours.

If your paper is very thin and loose, then wash it with this Allum water four or five times, letting it dry between every time, and your paper must always dry before you lay on any of your colours.

But take notice, that if you design to varnish your prints after they are colour'd, then wash the prints all over equally with white starch before you colour them, and when that is dry lay on the colours.

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