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gum-arabick, or fenega, to bind them together, 

 and make them ftick to the paper. If there 

 be too little gum, the colours will rub off if 

 you pafs your finger over the paper when dried : 

 if too much, the colours will lliine, crack when 

 very dry, and fometimes peel off. What I fay 

 muft always be undcrftood of water-colours, or 

 painting and colouring in water. Indigo muft 

 be ground with gum diffolved in water, and, 

 when well ground, dried in fmall drops, which 

 will be eafily reduced again to a liquid, in fair 

 water, fi^t for ufe. I have difcovered a fecret 

 relating to purifying indigo, which may be of 

 ufe : make a ftrong lye of pot-afli, then break 

 your rock-indigo pretty Imall, and put it into 

 the lye, fo that it be covered : it may ftand a 

 month or more. When you pour off the lye, 

 cover it with boiling water, fliifting it ëvery day 

 till the water comes from it pretty clear, and it 

 will be purified from all its filth 5 for the lye, 

 and many of the waters after it, will come from 

 it of the colour of very ftrong brown beer, while, 

 the bluenefs of the indigo is not extraded ; the 

 foul colour is drawn from the rotten leaves that 

 are maftied with the indigo when it is made up : 



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