MEDIUM-POWER PHOTO-MICROGRAPHY 



125 



stirrer, the quarter-plate negative is placed in a half-plate dish, in which enough 

 water has been added to just cover the plate. A fresh measure is then taken, the 

 water out of the dish emptied into it, and about a teaspoonful of the cyanide 

 cum iodi solution added. The newly mixed solution is then poured over the plate 

 as it lies in the half-plate dish and the effect carefully watched. If too strong the 

 thinning will proceed at an alarming rate, and the negative must be taken out and 

 washed in water or it will be completely destroyed. It is therefore well to proceed 

 with some caution, adding but little of the cyanide solution at first until the learner 

 has acquired some experience. Directly it is lifted out, and before looked at, the 

 plate should be rinsed very freely in water, for if not, streaks will be immediately 

 formed where the fluid runs down the gelatin, which cannot possibly be removed. 

 This precaution should certainly not he forgotten. After thorough rinsing hold it up 

 to the light with the ground glass between it and the flame, and let the operator 

 make up his mind whether he thinks it sufficiently thinned or not. If not, the 

 process must be renewed ; if sufficiently reduced return it to the sink, where it should 

 have at least one or two hours' good washing, besides a gentle rubbing over the 

 surface of the film as it lies under ivater with a piece of cotton wool. It is not 

 a little curious that stains may arise which hopelessly spoil the final result at this 

 stage if the washing be neglected, and therefore the operator is cautioned not to leave 

 this portion of the treatment to chance. 



If the photographer elects to thin the negative before the washing after fixing — 

 that is to say, directly he has taken the plate out of the hypo bath — he may proceed 

 as follows : The quarter-plate negative is placed in a half-plate dish and covered with 

 water ; this is returned to a oieasure, to which is added about a teaspoonful of the 

 concentrated solution of hypo already mentioned and about a drachm of a solution 

 of ferridcyanide of potassium (150 grains to 20 ounces of water). When mixed 

 thoroughly this solution is flooded over the negative, taking care not to pour it all 

 over one portion of the same, as by so doing it is possible that that portion so treated 

 will be more thinned than the rest. After a few seconds the film will appear more 

 transparent, and, if this process proceeds too rapidly, the solution should be diluted 

 with an equal bulk of water. Let the operator, until he gains experience, be careful 

 to rinse the negative under the tap each time before he holds it up to examine it 

 before the gas lamp, lest perchance his solution runs in tears down the negative. 

 If it does this, streaks will be formed down the picture which will hopelessly spoil it. 

 A good washing for two hours is necessary to eliminate the hypo, and let the plate 

 be gently rubbed with cotton wool soaked in water before taking it out to dry. 



