158 



UNDULATORY FORCES. LIGHT PHOTOGRAPHY. [THB CAI/>TYPB. 



6. The Toning Prtxtu. After willing tho plate, 

 place it on a ring-stand, BO thut it may ! quite level ; 

 aud thero U to DO i>oured on it thu Ml. nun;,- toning 

 mixture, so that every ]>art nf tin- picture may be 

 well covered. It is made as follows : 



ri.lo of gold ... 8 grains. 

 1 ' . r . . . 4 ounces. 



The salt of gold, having boon dissolved, is theu added 

 to tku following solution nf 



Hyposulphite of soda . . 25 grains, 

 r . . . 4 ounces. 



The two solutions, when mixed together, have a 

 slight yellow tint, which, however, passes off. Some 

 of this being poured on the picture, the heat of 

 a .spirit-limp is cautiously applied U-ncath each pait, 

 until minute bubbles ap]ar. In a short time, the im- 

 proving effect of the toning process becomes visible, in 

 the intensity and depth of contrast produced between 

 the light and dark parts of the picture. The plate may 

 now be left to cool, and tho gold solution is then to be 

 washed off, by means of distilled water, until the plate 

 is perfectly cleansed. The spirit-lam]) may now In- 

 to dry it; aud on this being carefully performed, the 

 whi ilc process may be considered as complete. 



\Ve have thus given a detailed account of the succes- 

 sive processes which enable us to obtain pictures on 

 silver plates by means of the Daguerreotype process ; 

 but have omitted numerous modifications and improve- 

 ments which have been from time to time suggested by 

 various operators, because the process is rapidly becom- 

 ing obsolete, in consequence of the greater value of, and 

 the better results afforded by, the various processes on 

 glass. It requires a considerable amount of care, a -id 

 some photographic experience, to obtain even tolerable 

 results ; and, as we before remarked, the silver plate has 

 tho great objection of reflecting light, so that the pi< 

 can only be seen at a certain angle. We are not aware 

 of any photographer who professes to take portraits by 

 this process at the present time ; and therefore we have 

 introduced the subject more as a curiosity, and as an 

 {'lustration of the earlier attempts at picture-taking liy 

 tin- agency of light, than as one of any utility or profit 

 to the experimenter. 



We may conclude by stating, that if any of our readers 

 upt the process, and arrive at the very common re- 

 sults of obtaining " spoilt plates," such may be employed 

 again by heating the surface to remove the mercury, and 

 then by repeating the process of cleaning, according to 

 the directions given in a previous page.* 



THE CHROMOTYPE PROCESS. 



fius process is so easily conducted as to be at the com- 

 mand of any one, however slightly acquainted with 

 science or experimental manipulation. It depends on 

 the fact, that certain salts of chromic acid are easily acted 

 on by actinic rays ; and the most proper for the purpose 

 is the bichromate of potass. 



A saturated solution of this salt is made in cold water, 

 in which any suitable-sized sheet of paper may be im- 

 mersed. The salt will soon penetrate its pores ; and tho 

 paper, after draining, is to be dried between folds of 

 i-uiiimon blotting-paper. It will thus have acquired an 

 orange-yellow tint, and it may be preserved for any 

 length of time if kept in a dark place. It is used iii 

 exactly the same way as the positive paper (de.-cribed 

 at a previous pagcf) in the copying frame. Tho 

 object is placed on the plate-glass: on this the chro- 

 matisod paper ; and the back of the frame is then I 

 into its place; or the object may be simply kept in 

 contact with tho prepared paper, by means of a sheet of 

 plate-glass. 



The time required for exposure, of course, varies ac- 

 cording to the chemical power of. the daylight. Tin- 

 exposed parts should, however, present a dark-brown 

 tint before the object is to be removed. 



The process of fixing is remarkably simple. The pic- 

 lure is soaked for some time in warm water, so as to 



See ante, p. 158. f gee ante, p. 154. 



dissolve out MIV unchanged bichromate of potass. The 

 paper will thus M n i OF, at all events, 



of alight primrose colour, in those pai ts w Inch : 



1 l.y the ubjei v. hilst the other parts pre- 



sent a dark-brown hue. 



This process may bo readily employed for copying any 

 t whose outlines are well defined such as lace, 

 ferns, tint shape of leaves, <vc. Indeed, with a child's 

 transparent slate, and a few sheets of paper, the In.: . 

 and others, may copy a vast variety of objects; and, 

 from the simplicity of the whole affair, it may all'ord an 

 instructive and interesting amusement to young people. 



THE CALOTYPE PROCESS. 



ONE of the most ardent and successful of all those who 

 have devoted their attention 10 photographic i 

 tions, has been Mr. Fox Talbot. From tii 

 of the art he has continually made contributions to our 

 stock of information ; and to him we are indebted for a 

 variety of improvements on the processes proposed 

 by other experimenters. 



So early as the rear 1839, Mr. Talbot communicated 

 his views to the Royal Society, in reference to " the art 

 of photogenic drawing, or the process by which natural 

 objects may be made to delineate themselves without the 

 aid of the artist's pencil." He also pointed out how 

 such impressions might be fixed or rendered unchange- 

 able by the further action of light. 



The earlier attempts at producing and retaining pho- 

 tographic copies were but of a comparatively \.ilu 

 character. The numerous causes of failure to which wo 

 have already so fully alluded, were only distantly gue 

 at ; and the eagerness with which each new discovery was 

 hailed, frequently prevented that close and philosophic 

 examination into the chain of circumstances which gave 

 them birth, or into tho causes of failure, which almost 

 invariably produced disappointment in those who at- 

 tempted to repeat the experiments of others. Wo can 

 well remember the obscure accounts which were published 

 from time to time, in reference to the different processes, 

 as they were given to the world. This, coupled with the 

 various opinions held by discoverers, by no means assisted 

 even the most ardent experimenter, but-rather left him 

 in what has expressively been termed "a fog." Tho 

 mists of uncertainty, however, were gradually dispelled ; 

 aud at the present time, photography stands out as one 

 of the most complete applications, both in rationale and 

 practice, of any which have been made of tho various 

 branches of science. 



These remarks are hero made, because we regard the 

 calotype as tho first elegant and complete branch of 

 photographic manipulation. The discoveries of Daguerre 

 were of great value ; but those of Sir. Talbot at least 

 equal them in that respect, and, in practical utility, often 

 exceed them. 



Having thus given a slight sketch of early photogra- 

 phic history, so far as it bears on our subject, wo now 

 proceed to detail Mr. Talbot's method of producing his 

 calotype pictures; and shall introduce the subject in 

 nearly the words used by the inventor whilst describing 

 his earlier processes. 



We may, however, impress on our readers tho remarks 

 which have been made in reference to the choice of paper. 

 It matters not what process is undertaken in photogra- 

 phy the same chemical laws must be observed, and 

 chemical changes must bo looked for or guarded ag ; 



The following, therefore, will guide the operator into 

 what wo may call the elements oi the calotype process. 



A proper paper having been chosen according to the 

 general instructions wo have already given, such is to bo 

 placed in a solution of nitrate of silver, dissolved in the 

 proj>ortions of 



Nitnite of ailvei . . . 100 -Drains. 

 Distilled water ... ounces. 

 In tho manner described at a previous page. J The 

 side so placed should be marked by means of a pencil, 

 that it may thereby be easily recognised. The paper U 

 t See uir, p. 1M. 



