244 PEACTICAL PHOTO-MICEOGEAPHY 



Fixing is effected in exactly the same way as with the 

 negative, except that fresh solution should be used for each 

 batch of plates, and it should be discarded the moment it 

 shows any sign of discoloration. An acid fixing-bath is 

 perhaps the most suitable, as it ensures that no stain results 

 from oxidation of the developing agent. It may be made by 

 adding about 20 grammes of metabisulphite of soda to each 

 500 c.c. of fixing-solution. 



To obtain a lantern-slide from a plate which is too large 

 to print by contact, recourse must be had to the reduction 

 process. The method consists essentially of re-photographing 

 the negative by means of an ordinary camera. The latter is 

 placed in such a position in relation to the negative that a 

 reduced image of it is thrown on to the ground-glass screen. 

 The negative is placed in front of the camera, and the latter 

 extended for such a distance that an image of suitable size 

 is seen. The negative may be illuminated by either daylight or 

 artificial light. The image is focussed as in ordinary photo- 

 graphy, and the lantern-plate put in the dark-slide and the 

 exposure made. There are many appliances to be obtained 

 commercially for this purpose. They may be had of fixed focus, 

 in which case they are only suitable for reduction from one 

 size of negative, or they may be variable for any size. The 

 important points to bear in mind are that the negative is evenly 

 illuminated, and that the lens used is such that it does not 

 impair the definition of the final result. 



Exposure depends on the intensity of the light used ; in the 

 case of daylight, from one to three minutes will usually suffice. 

 Development is carried out exactly as when making a slide by 

 contact. This method is rarely necessary in photo-micrography, 

 so that reference should be made to one of the manuals on pure 

 photography if further instructions are required. 



The positive having been fixed, washed, and dried, as in 

 negative work, it requires covering with a mask of black paper 

 to cut off any unsightly part of the edge of the image. It is 

 then placed in contact with another plain piece of glass of the 

 same size, so that the film is between the two. Lastly, the 

 edges are bound round with adhesive black paper, and the slide 

 is ready for projection. Lantern-slide making presents no 

 particular difficulty over any other photographic process except 



