152 Dr Fyfe on Vhotoyraphy. 



it is washed with water to carry off the whole of the am- 

 moniacal solution. It should, then, when nearly dry, be 

 subjected to pressure till dried, by which it is prevented 

 from wrinkling, and the impression retains its original sharp- 

 ness, which, unless this is done, it is apt to lose, by the fibre 

 of the paper being raised by the repeated moistening. 



Though the phosphate specimens may be preserved in this 

 way, yet they do not retain exactly their original appearance. 

 Those parts, whitened by the ammonia, owing to part of the 

 silver being united with the paper, gradually acquire a faint 

 reddish tinge, — but, though altering the appearance, it does 

 not affect the brilliancy ; indeed, in some cases, it rather im- 

 proves it, by giving a pleasing tint, which contrasts well with 

 the darker parts, and gives the appearance of colouring. I 

 have also found that carbonate of ammonia answers equally 

 well, and, being much cheaper, it will of course be preferred. 

 I generally employ a solution, prepared by dissolving one part 

 of salt in about four of water, in which the paper is kept for 

 a minute or so, and then afterwards washed, and subjected to 

 pressure, as already noticed. Impressions thus preserved ac- 

 quire the same reddish tinge as those acted on by ammonia. 



I have before stated that the paper may be prepared by 

 washing it over with a solution, procured by adding nitrate of 

 silver to carbonate of ammonia. The impressions taken with 

 that paper are easily preserved, by merely washing them with 

 water, to carry off the part not acted on by the light, which is 

 another advantage, in addition to those stated, for using the 

 carbonate solution. Like the phosphate specimens, they also 

 acquire a reddish tint. 



Other preservative methods have been recommended, as, by 

 covering the impressions with a yellow colour, to prevent, as 

 much as possible, the transmission of the chemical ray of the 

 light ; but those above stated, particularly when the phos- 

 phate or carbonate is used, are so simple and efficacious that 

 it is unnecessary to allude to them. 



Before finishing this part of the subject, I may here allude to a 

 valuable practical application of photography, in diminishing 

 the labours of the lithographer. In communicating the impres- 

 sion of any object to the stone, as of a dried plant, or in copying 



k 



