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UNDULATORY FORCES. LIGHT PHOTOGRAPHY. [BUY PROCKSBB. 



THE DRY COLLODION PROCESS. 



GRKAT inconvenience is felt by photographers in taking 

 views by means of the ordinary collodion process, owing 

 to the necessity of exciting the plate immediately pre- 

 vious to its being introduced into the camera ; and nume- 

 rous attempt* have been made to prepare plates which 

 would retain their sensitive condition for a length of 

 time after they have been excited. These have resulted 

 more or less successfully, but they still leave room for 

 improvement. It was at first proposed to use a salt 

 which would deliquesce, or absorb moisture from the 

 atmosphere, and so retain the collodion surface in a 

 proper condition for the camera. This plan was super- 

 seded by others, which seemed more convenient in prac- 

 tice. We can only refer to some of the latest improve- 

 ments, which are, more or less, modifications of previously 

 published processes: and we are indebted for the fol- 

 lowing ri'tumt of recent inventions, to the pages of the 

 Photographic Newt Almanac (1861). 



THE COLLODIO- ALBUMEN PROCESS. 



" THB plates should be very carefully cleaned for this 

 and all dry processes, and especial care taken that they are 

 perfectly dry before coating with collodion. The quality 

 of the collodion used is not of importance, so far as the 

 question of sensitiveness is concerned ; but for the bettor 

 prevention of blisters, etc., an old or powdery collodion 

 is desirable. The plate is coated and excited in the 

 regular way, and washed thoroughly in a running stream, 

 to remove free nitrate of silver. It is then coated with 

 a solution, prepared as follows : 



" Albumen .... 2 ounces. 

 Distilled water . . . -j- ounce. 

 Iodide of potassium . . 10 grains. 

 Bromide of potassium . . 2 ,, 

 Liquid ammonia . about 20 minims. 



"The iodide and bromide should be dissolved in the 

 water, which should then, together with the ammonia, 

 be added to the albumen, and the whole thoroughly 

 beaten to a froth. When it has settled, the clear 

 portion should be poured off, and kept in a bottle 

 for use. 



"The washed collodion plate is to be coated with this 

 whilst it is still wet. After it has drained a moment or 

 two, pour over its surface the albumen twice. The same 

 albumen may be used for two or three plates ; but after 

 that, it is better to take a fresh quantity. The plate 

 must now drain on one corner a few minutes ; then dry 

 it rapidly Ixjfure a clear, bright fire, and make it quite 

 hot. In this state it is not sensitive to light, and 

 will keep for many months. To render the plate sensi- 

 tive for use, it must be again immersed in a bath, pre- 

 pared as follows : 



" Nitrate of silver . . .40 grains. 

 Glacial acetic acid J drachm. 



Water 1 ounce. 



" After taking the plate out of the bath, drain a moment, 

 and then wash well under a stream of water. A plate 

 well washed always keeps longer, and develops cleaner, 

 than one washed insufficiently. After washing, drain, 

 and place it on blotting-paper to dry. The plate may be 

 dried artificially ; but will do so spontaneously in about 

 ton minutes. 



" Tho plates will keep ready for the camera two or three 

 weeks in summer, and as many months in winter ; but it 

 is better to use them fresh. 



" The development of the latent image is the most im- 

 portant operation in this process. It is slow ; but, on 

 that account, very manageable. If the plate is well ex- 

 posed, and free from blisters, there is no doubt of get- 

 ting a picture. There are two methods of development ; 

 with pyrogallic acid and with gallic acid. To develop 

 with pyrogallic acid, take the exposed plate, and place it 

 on a levefling-stand ; pour a little water over the sur- 

 face ; then talce a sufficient quantity of the following 

 developing solution : 



" Pyrogallic acid .... 2 grains. 

 Glacial acetic acid J drachm. 



Water i mince. 



And pour it over the plate repeatedly. When the sky 

 and high lights appear, add a fuw drops of a ten-grain 

 solution of nitrate of silver. This will bring out all the 

 details of the picture ; Imt when held up to the light, it 

 will appear weak and transparent. In this state more 

 silver should be added, until sufficient intensity is 

 gained. 



" During the development, it is more than probable that 

 the surface may bo marked by streaks or stains, or a 

 deposit may cover the whole plate. If this should 

 occur, stop the development; wash with water; and 

 with a piece of tine cotton wool, rub away these defects, 

 and go on again witli the development ; the horny 

 surface of the albumen allowing tliis to be done without 

 fear of damaging the negative. This is the great advan- 

 tage the process has over every other. The plate can be 

 developed for hours or days ; because, though a de- 

 posit falls, it can be wiped over and over again. This 

 is an immense advantage when the picture is under- 

 exposed, as it can be frequently brought out by long 

 development. 



"To develop with gallic acid, take the exposed plate, 

 and put it, face upwards, into a glass or other dish, with 

 a sufficient quantity of a saturated solution of gallic 

 acid to cover it. When it has remained five or ton 

 minutes, add a few drops of a ten-grain silver solution, 

 and mix well in the dish ; the picture will gradually 

 appear. When all the details are out, add more silver, 

 till the development is complete. 



" Whichever process of development be adopted, great 

 care is required to attain just the proper amount of in- 

 tensity, and no more. In all processes where albumen 

 is used, the real printing intensity is much greater than 

 it at first appears, owing to the light-resisting colour of 

 the deposit. There is great danger of over-development, 

 as some photographers are not content until the sky is 

 quite black ; at which time, in an artistic point of view, 

 the picture is quite ruined. 



" The picture is fixed with hyposulphite of soda, in the 

 proportion of five or six ounces of the salt to the pint of 

 water. Cyanide of potassium would act rapidly on the 

 organic deposit, and is therefore unfit for use." 



THE FOTHERGILL PROCESS. 



FROM the same authority, we quote the following parti- 

 culars of a modification of the Fothergill process ; so 

 called after its inventor. 



" For coating the plates, take of old iodised collodion, 

 containing one grain of a bromide, in addition to four of 

 iodide, one part ; and of a newly iodised collodion, con- 

 taining iodide only, one part. The glasses must be 

 carefully cleaned, and quite dry when coated : a thirty- 

 five grain nitrate bath, with a very slightly acid reaction, 

 is the best sensitising solution. The plates, wlu-n excited, 

 must be washed in a limited quantity of distilled water. 

 A solution is then required ; prepared as follows : Of 

 albumen, from fresh eggs, one ounce; of water, three 

 ounces ; of the strongest liquid ammonia, a few drops to 

 each ounce of the preparation ; and also a few grains of 

 citric acid. The plate is coated with this preparation, 

 which is left on it a few minutes ; it is then to be tho- 

 roughly washed in water, and dried. Plates so prepared 

 are very sensitive, and possess good keeping properties." 



We have chosen the two processes above described, 

 because they are comparatively easy of prosecution. A 

 variety of substances, of a vegetable kind, have been 

 employed as preservatives ; such as linseed, malt, 

 glucose, <bc. ; but our limits forbid us entering into 

 special details respecting them. 



Our readers will perceive, that many precautions have 

 to be observed to ensure successful results ; and their 

 patience and perseverance will doubtless be well tested. 

 At the same time, a really good negative is an ample 

 reward for all the pains we can bestow ; whilst an inferior 

 one is, at all times, valueless for printing purposes. 



