20 



HOW TO PHOTOGRAPH 



of the negative, with Bates' or Fallowfield's 

 black varnish. It will be easy to follow 

 with the brush the regular outlines of the 

 diatom ; but should any varnish trespass on 

 the edges, don't wipe it off, but let the 

 whole dry. When dry, hold the negative 

 up tothj light, and go round the edges of 

 the image with a fine pointed penknife 

 cutting away in an even manner any var- 

 nish that intrudes on the edge of the pic- 

 ture. The varnish should come exactly up 

 to the edge of the image ; there should be 



no intervening space, or failure will ensue. 

 The negatives treated thus should always be 

 printed in the shade — a powerful light 

 would produce an objectionable black halo 

 round the object. All objects which have 

 regular outlines should be thus treated if 

 necessary. 



The Arachnotdisc?is figured below had 

 an exposure of fifteen minutes, with Swift's 

 low angle |^-inch eye-piece and small mi- 

 croscope lamp. This exposure brought out 

 the diatom sharply and with due printing 



AkACHNOIDlSCUS INDICUS ^ 300. 



density, but the background was weak, and 

 would have printed in with a most objec- 

 tionable blackness had not the plan of 

 " painting out " been practiced. 



Parts which come out insufficiently dense 

 may be strengthened on the film side of the 

 negative with a soft blacklead pencil. This 

 is best done after the negative has been 

 varnished, using a little turpentine t o 

 roughen the part to which the pencil is to 

 be applied. 



Local reduction has often to be effected, 

 and can easily be done by using the ferricy- 



anide reducer given above, "Wet the nega- 

 tive thoroughly ; when the excess of water 

 has drained off, dip a fine brush in the solu- 

 tion and apply to the over-dense parts. As 

 each dense place is reduced, dip the nega- 

 tive in water to stop the reducing action 

 and proceed with the next part. 



It will often be found that, no matter 

 what skill may be expended on the negative 

 in strengthening the weak parts and reduc- 

 ing the dense ones, it is impossible to get a 

 harmonious print. Some parts will print in 

 strongly long before other parts are done. 



