14 



Proceedings of the Boyal Irish Academy. 



paper. Tlie printer's varnish, is in all good printing ink linseed oil, 

 more or less oxidized — but the oxidation may vary in degree from its 

 first stages, known as ordinary drying oil, and made by the action of 

 acetate of lead upon linseed oil, or it may be burnt until it becomes 

 a stringy varnish that can be drawn into threads. 



The first is a fluid linseed oil hardly changed in its properties, 

 whilst the last is a tough resinous mass scarcely soluble in oils, and 

 quite altered in character from the original compound. This last may 

 be considered as a glyceride of lineolic acid. 



I have found that the older printing inks are more easily saponi- 

 fied and washed off by alkalies, than those of the last century, and 

 that in this respect there is a marked difference. In their general 

 character they agree, as carbon seems to- have been the basis of 

 printing ink from the time of Johann Paust, and from this reason 

 printed matter will bear the action of acid oxidizers, or bleachers, with 

 impunity ; but many, if not all, the printing inks of the fifteenth 

 and sixteenth centuries are more or less sensitive to the action of 

 alkalies. Some specimens are so extremely sensitive to this alkaline 

 influence that on introducing them into a weak solution of ammonia, 

 the characters instantly float off the surface of the paper, although 

 they may have previously withstood the action of a powerful acid 

 bleaching bath. The only explanation that I can offer is that the oil 

 or oils used as vehicles were not formerly submitted to the boiling 

 process, which in the more modern inks has thoroughly resinified 

 them. 



It is also probable that copaiba or other balsams were freely used 

 in the more ancient inks. These balsams are easily acted upon by 

 diluted alkalies. 



It will be seen by the following details that this peculiarity was 

 not confined to one country. * 



Inlc insoluble, or nearly insoluble in 

 alkalies. 



Yarious pamphlets published in 

 England and Ireland, 1720 to 

 1730. 



Modern English Inks, all the 

 specimens tried. 



Modern Leipzig Ink. 



InTi soluble in diluted ammonia. 



" Agricola. De re metallica," 



Basilefe, 1561. 

 Some of Albert Durer's plates. 

 "Libri Solomonis," Paris, 1542. 

 " Titi Livii Historiarum Libri," 



Amsterdam, 1635. 

 "Le Martyrologe Romaine," 



Lyons, 1636. 

 "Portraiture of his Sacred 



maiestie," London, 1648. 



