DECORATIVE NATURAL HISTORY WORK. 109 



turned to the ordinary commercial sea-green (from 

 which we may conclude that it is useless laying in a 

 stock of both tissues). Leave it a little longer, and a 

 brilliant apple-green results ; longer 

 still, and you will approximate to 

 yellow. Take another blue trans- 

 parency and immerse in a five per 

 cent, solution of persulphate of am- 

 monium : it will be slightly reduced 

 and approximate in colour to the com- 

 mercial engraving black. Indefinite 

 changes can be rung with the other 

 tissues by the use of various dyes 

 Each particular effect must be learnt 

 by experiment, but it is not too much 

 to say that, with the five or six 

 ordinary commercial tissues, and a 

 supply of simple aniline dyes, any 

 desired colour can be approximated 

 to. 



Moreover, the supply of material 

 from which one can form a backing 

 for the transparency is practically un- 

 limited in its variety metal, wood, 

 opal, thick plate glass, paper of any 

 kind, colour, or texture and yet how 

 many thousands of photographers are 

 there who employ nothing but silver 

 papers with their hideous and uncertain 

 tones, or platinum tristissimum ! Nor 



Treefrog. 



