NOTES ON THE PHOTOGRAPHIC TECHNIQUE 

 which are virtually indistinguishable from originals. One method is to make a paper 

 negative by treating the drawing as a transparency and making a contact print of it 

 on to any slow contrasty printing paper. The two pieces of paper should be kept closely 

 in contact with the unexposed sensitive surface against the drawing either in a printing 

 frame or by other means. Illumination is through the back of the drawing, and a 

 negative print results, from which positives may be obtained by a repetition of the process. 

 Any ordinary gashght paper can be used, though Ilford Reflex Document paper no. 50 

 was found specially suitable and cheaper than gaslight paper for large diagrams. 



(d) Duplication of drawings by reflex copying. If a drawing is much touched up, or has 

 writing on the back, or is on rather opaque paper or board, it may be inconvenient to 

 illuminate through it, and in that case reflex copying is to be preferred. The drawing is 

 placed face upwards and is covered by a piece of Ilford Reflex Document paper no. 50 

 with the sensitized side downwards. Close contact is essential, and may be obtained 

 either in a printing frame or by covering with a piece of glass held down by weights. 

 Illumination is through the back of the Reflex Document paper. The length of exposure 

 can easily be ascertained by trial, but an average duration is 20 sec. with a 60 W. bulb 

 at 2 ft. After development a paper negative is again obtained, from which positives may 

 be printed off" by normal contact methods. 



(e) Silhouettes of fern leaves. A paper negative is made by putting the leaf in contact 

 with slow contrasty sensitized paper and exposing it as if for a photographic print. The 

 use of a printing frame is convenient if the specimen is small and ordinary contrasty 

 gaslight paper to be used. If the specimen is large or a part of a herbarium sheet which it 

 is inconvenient to disturb, Reflex Document paper may be preferred, placed either above 

 or below the specimen (cf. (c) and (d) above). The negative so obtained may be used 

 for printing off" positives in the usual way. This method is very valuable, since complete 

 accuracy and great speed are obtained at very small cost. 



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