LEAVES 149 



Series of blue prints illustrating forms of apex, base, mar- 

 gin, shape, and any other conspicuous features may be so 

 prepared, also many flowers, flower clusters, and such deli- 

 cate objects as thistledown, milkweed seeds, and feathers. 



Formula for Blue Print Paper 



Solution I. Potassium ferricyanide . . 1 oz. 



Water (distilled) 5 oz. 



Gum Arabic 1 drachm 



Solution II. Iron-ammonia citrate (green) 1| oz. 



Water (distilled) 5 oz. 



Gum Arabic 1 drachm 



Directions for using Mix equal parts. Coat paper in 

 the dark by use of oil lamp or yellow light. Dry the paper 

 quickly by heating and keep it in a dry, dark place. Select 

 by preference a paper which has a good sizing, such as fools- 

 cap. The mixed solution should have a wine color, and the 

 dry paper a lemon yellow. Print until the dark parts are 

 bronzed and wash the paper thoroughly in cold water. 

 Prints can be brightened by adding a trace of citric acid 

 to the last water. 



Note. No rule can be given for the time required for exposure, 

 since blue print papers vary in sensitiveness to light and the objects 

 used are so different in thickness. Thus the so-called " French- 

 satin-junior " paper is very sensitive, while many of the common 

 papers used by architects require a great deal longer time for ex- 

 posure. Objects like feathers, thistledown, and semitransparent 

 leaves may require but a minute, while old leaves may be exposed 

 for an indefinite time. 



A little practice will show the experimenter how to get the best 

 results. 



