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There is another method of giving blackness to inks, bythe addition of some of the black pigments formerlymentioned; but the use of these pigments for writingwill make the subject of another article at the end of thissection.

As the galls and logwood ought to be in pretty finepowder, that their virtue may be more readily and effec-tually extracted, it is expedient to have the ink separatedfrom them, as in the second of the above processes; be-cause otherwise the ink will often be loaded with thefiner parts of the powder in substance, which being mixedup by ihaking the vessel, remain long suspended in theliquor. It is proper, however, in order to secure againstany danger of a deficiency in the astringent materials, toadd to the ink separated from its feculence, some galls incoarse powder freed from the fine dust by a sieve. Onthe same principle, an oaken cask is one of the best vesselsfor keeping ink in, this wood having a manifest astrin-gency, and answering nearly the fame end with the addi-tional galls. Besides the galls, some pieces of iron may beput into the vessel, as mentioned in page 386.

III. Of the preparation of the paper for durable writing.

The dyers, as we shall fee hereafter, prepare theircloth for receiving a permanent black colour, by boilingit with galls, that it may be thoroughly penetrated by theastringent parts of the galls before the vitriol is intro-duced ; so that wherever the vitriol can reach, it meetswith astringent matter, to unite and produce a black with.

It is observable, that writings first begin to fade orchange their colour on the back of the paper, where thelarger strokes have funk in or are visible through it •, as ifpart of the irony matter of the vitriol was in a moresubtile or dissolved state than the rest, and sunk further

into