*76 M.- [Book VI. 



yellow in conrequencc of the decay of the vegetable 

 matter. Their legibility may be reftored by the ufe 

 of infufion of galls, or gallic acid. The beft method, 

 however, of refloring the legibility of ancient writings, 

 confifts in fpreading a folution of the Pruffiari alkali 

 thinly with a feather over the traces of the letters, and 

 then to touch it gently, and as nearly upon or over 

 the letters as can be done, with a diluted acid, by means 

 of a pointed flick. 



The only eflential ingredients of ink are green vi- 

 triol, galls, and water. Dr. Lewis has made many 

 ufeful experiments on the proportions of thefe ingre- 

 dients which produce the beft ink. He found that 

 equal quantities of galls and green vitriol produced 

 the deepeft colour, but not the moft durable , he 

 found, that by increafing the quantity of the galls the 

 colour was rendered more durable; that with three 

 times the weight of the galls tb one of the vitriol, the 

 colour was very permanent j but that if the propor- 

 tion of galls was increafed beyond this, the colour 

 was too weak ; in this cafe the writing was much re- 

 frefhed by wafhing it with a folution of vitriol. He 

 alfb endeavoured to alcertain the beft proportion of 

 the fluids to the vitriol and the galls. He firfl tried 

 water, and found that by confiderably diminishing the 

 quantity of it the ink was more durable, but too thick 

 for ufe. He found that all waters were much the 

 fame; that white wine and vinegar made a more 

 durable ink ; but that both thefe were exceeded by a 

 decoction of forty ounces of water to one of logwood, 

 which of itfelf gives a permanent red ftain. If the 

 colour of the ink iliould fail, that of the logwood will 

 remain, and it produces, with ink, a much ftronger 

 and blacker colour than ufual ; for the common colour 

 of ink is a purplifh blue, which, mixed with red, 



makes 



