[ 17 ] 



III. Method of p7-eparing the Dutch Turnfol Blue *. 



T is well known that the Dutch kept their procefs for pre- 

 paring turnfol blue a very great fecret; and, in order to 

 miflead the public, pretended that it was made from rags 

 dved with the juice of the fun-flower (Hdlianibus), from 

 which it obtained its name. Since the late revolution, howT 

 ever, in Holland, the true method employed by the Dutch 

 for preparing this colour has been difcovered, and the procefs 

 is as follows : — ^That kind of lichen called orchil {Lichen ro~ 

 cella), or when that cannot be procured, the large oak mofs, 

 after being dried and cleaned, is reduced to powder, and by 

 means of a kind of oil-prefs the powder is forced through a 

 brafs fieve, the holes of which are fmall. The lifted powder 

 is then thrown into a trough and mixed with an alkali called 

 'vetas, which is nothing elfe than the afhes of wine lees, in 

 the proportion of half a pound of aflies to one pound of 

 powder. This mixture is moiftened with a little human 

 urine, for that of other animals contains lefs ammonia, by 

 which a fermentation is produced; and the moiftnefs is ilill 

 kept up by the addition of more urine. As foon as the 

 mixture aflumes a red colour, it is poured into another 

 trough ; is again moiftened with urine, and then ftirred 

 round in order that the fermentation may be renewed. In 

 the courfe of a few days it acquires a blueifli colour, and is 

 then carefully mixed with a third part of very pure pulve- 

 rifed potalh ; after which 'the mixture is put into wooden 

 pails, three feet in height, and about half a foot broad. 

 When the third fermentation takes place, and the pafte has 

 acquired a confidcrably dark blue colour, it i° mixed with 

 chalk or pulvcrifed marble, and ftirred well round that the 

 whole may be completely united. 'J his laft fubllance gives 

 the colour no higher quality, and is intended merely to add 



■ I'roni the Jloulluti^fzciltni?, bv ]. A. Hil.Jt, for Dc-C!.i.'jbtr 179S. 



Vol. IV. " C to 



