20 PHOTO-MICROGRAPHY 



Lumiere's plates are much prized by some photographers, but we have little fault 

 to find with the medium isochromatic plates manufactured by Edwards. They are 

 most uniform in grain and similar in sensitiveness, easy to develop, and very free 

 from fog, both when using hydrokinone or pyro. We know that others are strong 

 advocates of the Ilford isochromatic plate, but must admit that although they are 

 cheaper we have never felt any inclination to substitute them for the brand previously 

 mentioned. In conclusion, whilst making these comments, it should be distinctly 

 understood that many of our friends have different experiences, some preferring one 

 make and some another, and we think it only fair to say so. 



Every plate must be " backed," and we have no reason to find fault with the 

 "backing-" solution sold in tubes under the name of " Forrester's Effective Backing." 

 It must be dabbed on the glass with a pad and not smeared, as smearing leaves 

 streaks which frequently show in the final picture. The reason of that is this : 

 When a plate is not " backed" at all, the direct rays impinging upon the film, passing 

 through the emulsion, are reflected off the back of the glass again into the film at 

 definite angles, which depend upon the thickness of the glass and its refractive index. 

 When a plate is " backed," however, these are absorbed by the " backing," and if that 

 is unequally distributed some of them escape, whilst others are absorbed. This would 

 in some cases not so much matter, but as "backing" always sensibly increases the 

 exposure, so if the " backing" be well distributed over one part of the plate and not 

 on another, the bad results referred to are really due to differing exposures on one 

 plate, which are readily manifested when the negative is developed. 



In the present day most plate-makers sell their plates ready " backed," which 

 is a great convenience, for home "backing" is at the best of times a messy 

 matter. Edwards's "antihalo" isochromatic plates are really exactly the same 

 as those unbacked, which is mentioned here as some have thought they are 

 coated with a slower emulsion. This is not true ; their apparent slowness is due to 

 the fact that all " backed" plates require more exposure than those which are not so 

 treated. 



Being now prepared to take our photograph we will go practically through the 

 process from beginning to end. The mixed limelight being ready, the camera is set 

 in position, the object being placed upside down on the support S. The rays of the 

 limelight are made to converge in such a manner that their point of union is on the 

 lens side of the support shown in Fig. 9 by the thick lines, the dotted ones being 

 the incorrect position. In uur experience this is imperative to obtain a good image. 

 This is readily done by pushing the limelight to and fro, that is to say, nearer or 



