148 



UNDULATORY FORCES. LIGHT PHOTOGRAPH Y. [THB BENBITITB PROCESS. 



subsequent processes, except that of taking the like- 

 new, are conducted in what U called a dark room. 

 This room, in the language of photography, is con- 

 sidered to be a place into which not a ray of light of any 

 sort, except of a deep yellow colour, U allowed to enter ; 

 KM.-II ray, as we have already remarked,* having little or 

 no action of a chemical nature on the sensitive plate. 

 The pruffftsional or amateur photographer often goes to 

 considerable expense in arranging this " sanctu* tancto- 

 rum." We have had the good fortune to see a considera- 

 ble variety, even from a room fitted with every conve- 

 nience which science and means would permit, to one 

 wherein a crazy four-post bedstead, covered with ex- 

 tn-mi-ly aiu-ifnt bed-furniture, did duty in the waggon 

 of a travelling operator. Leaving the choice of position 

 or place to our reader, we may remark, that an abundant 

 supply of soft water running from a tap, a sink to carry 

 away waste water, a large firm table, and complete 

 absence of daylight, are the essentials of such a place. 

 A sitting-room may be used in which the windows arc com- 

 pletely closed from external light by means of thick 

 brown paper pasted over them ; and the water-supply 

 may be that of a jug and pails, with such other contri- 

 vances, when circumstances render greater conveniences 

 unattainable. 



Of course light of some kind must be used to enable 

 the operator to proceed. Some persons employ a tallow 

 candle, others a low gas-flame ; but both of these have a 

 prejudicial effect on sensitive plates. In some instances 

 a little daylight is admitted through thick orange- 

 coloured glass. We have always preferred to use a 

 spirit-lamp, charged with spirits of wine, in which dried 

 taUe-salt has been dissolved. This affords a flame of a 

 dingy yellow colour, perfectly inactive, from the absence 

 of chemical rays affording both sufficient light to work 

 by, and also a ready and necessary source of heat when 

 the plate has to be dried, (fee. , after fixing and washing. 

 It is essential that the dark room should t>e kept scrupu- 

 lously free from dust and dirt, otherwise it is more than 

 likely that such will settle on the delicate collodion film, 

 and spoil the plate. It is a good plan to wet the floor of 

 the room, especially in summer-time, which will prevent 

 the fine particles of dust rising as the operator moves to 

 and fro. 



A cleaned glass plate being held in the hands, the 

 iodised collodion may be poured on it in the manner 

 represented in the annexed engraving. The plate should 

 Fig. 154. be held quite 



horizontally in 

 the left hand ; 

 the collodion 

 bottle being 

 placed over the 

 centre, so that 

 the liquid may 



/,/ *^f&lp*^-~/ spread evenly 



over every part 

 until the edges 

 we reachc-d without its overflowing them. The object is 

 to give a thin and perfectly even film to the entire 

 surface of the glass ; and when such is obtained, the 

 superfluous collodion is to be poured off by holding the 

 plate over a wide-mouthed glass bottle, so that its 

 diagonal may rest on the neck. (See Fig. 155). The 

 plate is then to be restored to an horizontal position for 

 Fig. 153. a few seconds, in order that the 



regularity of the film may be re- 

 gained. This operation is one re- 

 quiring both care and practice ; and 

 can only be successfully performed 

 after the operator has had some little 

 experience. It should, however, 

 be done calmly, and without haste, 

 to ensure good results; and it is 

 advisable not to proceed further 

 with any plate which does not pre- 

 sent an even coating. Such are 

 easily cleaned for another trial, in 



8w anlr, p. 50. 



the manner already described, t Great care is to be 

 observed in the mode of removing superfluous collo- 

 dion after the glass plate has been covered with the 

 liquid. 



Presuming that an even, spotless, and otherwise per- 

 fect film of iodised collodion has been obtain. .1. t)n> next 

 step U to render this sensitive to light, which we will 

 now proceed to describe. 



3. To render the Coated Plate Sensitive. The choice 

 of a "bath," as it is termed, for rendering a coated 

 plate sensitive, has been a subject of great discussion 

 amongst photographers ; and almost every authority 

 has propounded views and directions, which, from 

 tln-ir diversity, are eminently qualified to perplex a 

 beginner. 



Although a middle course is at all times the safest in 

 which to steer, it is most difficult to find that position. 

 Some have recommended a proportion of nitrate of silver 

 in solution as the most sensitising, which is much less 

 than half the quantity, that others consider essential to 

 success. It has hence been found necessary to include 

 various recipes in all of the works which have been pro- 

 duced that deal with this subject ; and the recommenda- 

 tions, both scientific and empiric, which have thus been 

 published, may safely be called " legion." 



We confess to a difficulty in recommending any speci- 

 fic course to our readers ; but we shall do well to inquire 

 into those contingencies which may affect the best 

 formulae. ; and afterwards we shall endeavour to suggest, 

 not ex cathedra, but in deference to the opinion of every 

 one who may differ from us, as to what is the best course 

 for the student to pursue. 



The object which we have to attain, is that of making 

 the coated plate sensitive to the action of the chemical 

 rays of light ; and this should be so effected as to require 

 the shortest possible exposure in the camera to produce 

 the picture. For this end, a salt of silver must be 

 formed on the surface of the iodised collodion plate, 

 which will meet our demands. The difficulty lies in satis- 

 fying all the conditions which are essential to success. 



It would appear, at first sight, that the simplest mode 

 of rendering a plate sensitive, would be that of im- 

 mersing it in a solution of nitrate of silver, of any 

 strength within certain limits ; but it is found in prac- 

 tice, that the result of developing depends very much on 

 the strength of the silver solution employed. Again, 

 unless the ' ' bath" is prepared by the addition of certain 

 substances, the sensitive character of the film will be im- 

 paired, owing to a loss of a portion of its iodine when it 

 comes in contact with the silver solution. Even the 

 constitution (if we may so call it) of the film itself, in a 

 mechanical point of view, may be either modified or in- 

 jured by neglecting certain precautions. 



The student must not suppose that we are presenting 

 imaginary difficulties in his way. We are only anxious 

 to anticipate circumstances with which he may have to 

 contend ; and thus by giving him preparatory hints, we 

 hope to enable him to avoid both the Scylla and Charyb- 

 dis of photographic manipulation. 



From our own experiments, we recommend the fol- 

 lowing silver solution as an average one : 



Nitrate of silver 60 grains. 



Distilled water 2 ounces 



Iodide of potassium .... 1 grain. 



Dissolve the nitrate of silver first in an ounce and 

 a half, by measure, of distilled water; the iodide of 

 potassium may then be dissolved in the remaining half- 

 ounce of Water. The two solutions should then be 

 mixed and agitated together in a clean glass-stoppered 

 bottle, and subsequently filtered through clean filtering- 

 paper. This solution we have found to act well with 

 good positive collodion. When, through repeated use, it 

 has become replete with iodide of silver, a further 

 addition of a solution of the nitrate of silver, without 

 the iodide of potassium, should be made ; and the whole 

 is then to be filtered. A few grains of kaolin, or pipe- 

 clay, may be added to neutralise an excess of free acid 

 which will occasionally be present. 



4 MM unit, p. 146. 



