150 



UNDULATORY FORCES. LIGHT PTTOTOGRAPHY. [DBVBLOPINO AND FIXINO. 



We would here urge on the operator to employ each 

 resael in ni> photographic practice fur its special use 

 only. By ao doing, he will avoid any rink of mixing 

 notation*, and of thus rendering them useless. Every 

 chemical agent employed throughout the processes we 

 have already mentioned, and are yet to describe, must 

 only be brought together when wanted. If mixed care- 

 lessly, each solution, if present in only minute propor- 

 tions,' will certainly impair, if not destroy, the utility of 

 any other. A place (or vessel) for everything, and 

 everything in iU place, should be a golden rule in 

 photography. 



The plate being thus arranged, the developing solu- 

 tion should now be poured on to it from a glass mea- 

 Fi. 1S8. sure, similar to that represented in the 

 annexed figure ; and this should be done in 

 a careful manner, so that the whole of the 

 plate surface may be covered evenly with the 

 liquid. The latent image will now gradually 

 appear; and much care is required that the 

 process is not carried too far, for fear of 

 spoiling the picture. We must, of course, 

 therefore leave the study of its indications to 

 the judgment of the operator, who, although perhaps 

 failing at first to arrive at the exact point at which 

 development should stop, will eventually, after a few 

 trials and failures, acquire the necessary experience. As 

 soon as the picture is sufficiently brought out, all further 

 action should be stopped by washing the plate well 

 with cold water. This may be done by holding it 

 comerwise under a gentle stream of water running 

 from a tap, or by pouring water in abundance from a 

 jug with a narrow lip. It is extremely essential that 

 this washing should be as complete as possible, so that 

 every trace of soluble matter may be removed. This 

 being effected, the next step will be that of "fixing" 

 the picture. But before we proceed to that, we must 

 give our readers recipes for making the developing 

 solutions to which we have been referring. 



It will at once be perceived, by looking over the 

 annexed list of solutions, that considerable latitude is 

 assumed by various photographers. This is partly owing 

 to the varying nature of the collodion employed ; to the 

 manipulation of the operator ; and, in many instances, to 

 the peculiar views of those who follow the art. We have, 

 however, deemed it desirable, for the purpose of making 

 our subject as complete as possible, to lay before the 

 student ample opportunities for the exercise of his skill, 

 judgment, and choice, with respect to solutions. 



Developing Solutions for Positive Pictures. 



Protosulphate of iron .... 40 grains. 



.Nitric acid 3 drops. 



Acetic acid 30 ,, 



Alcohol 20 



Distilled water 1 ounce. 



Or 



Protosulphate of iron .... 8 grains. 



Acetic acid 1 drachm. 



Nitric acid 2 drops. 



Water . . .. 2 ounces. 



6. Fixing the Picture. The last-described process hav- 

 ing fully developed the latent picture, it only remains 

 to secure this from further change by the action of 

 light. The result produced is simply that of remov- 

 ing every trace of those salts of silver which would 

 become changed if white light were allowed to impinge 

 on their surface. 



There are two fixing agents which are chiefly employed 

 by photographers, each of which has the power of 

 removing the sensitive silver salts : these are the hypo- 

 sulphite of sodium, and the cyanide of potassium. The 

 first-named of these salts was largely used in the early 

 stages of photographic practice ; but at the present time, 

 the cyanide of potassium is mostly employed as a fixing 

 agent ; and as such, we have, from our own experiments, 

 to add our testimony to its value. 



The process of fixing is extremely simple. Either of the 

 following solutions being employed they are to be poured 



over the developed picture, and a portion is to be retained 

 on its surface ; or the plate may be dipped into a dish 

 containing the solution, and be gently moved about in it. 

 The soluble and changeable salts of silver are thus re- 

 moved, and any risk of injury ia entirely prevented when 

 the picture is subsequently exposed to daylight. After 

 r.'iii.-uniir,' in the fixing solution for about two minutes, 

 the plate should be abundantly washed by means of soft 

 water. We al'vays employ distilled water in the last 

 washing; because river and spring water contain salts, 

 which are left, to a minute extent, on the surface of the 

 plate, and so dim its lustre, and, consequently, lessen 

 the brilliancy and purity of the picture. 



After the picture is thus thoroughly cleansed from 

 every impurity, it may be left to drain, and to dry gra- 

 ilu.illy. The usual method, however, is to hold it fur a 

 short time over a spirit-lamp or gas-flame ; which, of 

 course, speedily causes the evaporation of all moisture 

 from its surface. 



For all ordinary purposes the picture may now be con- 

 sidered finished, with the exception that it requires 

 coating with a black varnish ; which has the twofold effect 

 of preserving the collodion film from injury, and of also 

 increasing the effect of light and shadow. This varnish 

 is sold by all photographic chemists ; or it may be made 

 by dissolving a little black asphalte in mineral naphtha. 

 This should be poured on to the collodion surface, and 

 left to dry. Some persons varnish the collodion surface 

 with the best white mastic varnish, before applying the 

 black coating. 



Either of the following solutions may be employed to 

 fix the picture. In that of the cyanide solution we have 

 given considerable latitude ; but it is advisable that the 

 student should commence with a weak solution, and 

 continue its use until his experience is sufficient to guide 

 him safely in the employment of stronger kinds. 



Fixing Solution*. 



Hyposulphite of sodium .... 4 ouncos 



WaW 1C 



Or 



Cyanide of potassium 6 to 12 grains. 



Water 1 ounce. 



It will be unnecessary for us to enter, at present, into a 

 description of the modes of colouring positive collodion 

 pictures, because we shall refer to this in a separate 

 article. We may, however, mention a few causes which 

 lead to failure in the early attempts of those unacquainted 

 with the delicacy of photographic practice ; and we shall 

 discuss these in detail. 



First, we may refer to the cleaning of the glass plate. 

 This, we already have stated, is a matter of the highest 

 importance, and sometimes one of some difficulty, because 

 of the nature of the glass itself. The electrician is well 

 aware, that no two circular glass plates, in the plate 

 machine, will give oft' an equal amount of electricity 

 when similarly employed, although they may be of 

 exactly the same size. This is chiefly owing to the 

 chemical constitution of the glass. Now, similarly in 

 photography, the quality of the glass, to some extent, 

 influences the photographic result; and such being the 

 case, the operator cannot be too cautious in the purchase 

 and choice of the plates he employs. In cleaning the 

 plates, every precaution should be taken to prevent the 

 presence of grease, grit, or dirt of any kind ; and the least 

 touch of the finger on any part of the cleansed surface, will 

 most certainly produce an ugly spot at that place. Cloths, 

 die., used from time to time, gradually acquire grease 

 and animal matter from the hands of the experimenter, 

 and so communicate objectionable matter to the plate. 

 Hence, an abundant supply of clean cloths is essential 

 to success in the earlier steps of taking collodion pic- 

 tures. 



The collodion itself varies, according to the source 

 whence it is obtained. Each maker considers his to be 

 the best ; but we advise the student, after making re- 

 peated trials, to keep to that which he finds to suit his 

 purpose, and not to heed the various recommendations 

 of his friends, or others, unless they are backed by 



