ISO 



PHOTOGRAPHY 



the |.aper was salted only i.e. the albumen WM 

 dis|>--n--d with and this old method is being largely 

 revived.) 



(2) Silvering of the paper by floating it mi a 

 solution of nitrate of silver, from 30 to BO grains of 

 this substance iving used for every ounce of water, 

 according to the amount and kind of chloride in 

 the papei. It is afterwards dried. 



(3) Kx|Misiire to light. The silvered pajpcr is 

 expos.-.! lieneath the negative in a printing frame, 

 the linn- of exposure varying according to the 

 brightness of the light and the character of the 

 negative. 



(4) Toning. In order to give a pleasing colour 

 to the print it is usual to tone it in a solution 

 of chloride of gold. Quite recently the metal 

 platinum has been used for toning silver prints on 



Klain paper with very fine result*. One method 

 as been introduced by Hlanohard, and another by 

 Lyonel Clark, the latter employing the same salt, 

 the chloro platinite of potassium, which is used for 

 the platinum printing process to be presently 



(5) Fixing. The print, when taken from the ton- 

 ing hath, is stecjK'il in a sdluiioii of hyposulphite of 

 so<la, which rt-nioM-s the undarkened silver salt that 

 in Klill sensitive to light, and so fixes the image. 



(6) Washing. Silver prints require to lie washed 

 quickly ami thoroughly after treatment with the 

 hyposulphite of nla. Prolonged soaking is harm- 

 ful, anil inipei-feetly wa-lii-d prints soon s|Hit and 

 faile. lielatinc is now largely coming into use as 

 a -nli-iitnic for alhumen : it is more suitable for 

 lli'' rendering of delieate detail, and the prints 

 with due care exercised in their production ought 

 to he more permanent. The pu|iers known as 

 Aristotype, Argentoty|H'. and Celeroty|>e are gela- 

 tine emulsions of clilomle of silver spread on paper. 



Printing in Suits nf Iron. The metal iron in 

 some of its chemical preparations is now MTV 

 largely employed in a number of photographic 

 printing processes e.g. cyanotype, chrysotype, 

 kallityjie, platinotyjie, &. and is capalile of 

 producing result* with all the fidelity and delicacy 

 of the silver process, in some cases at considerably 

 less cost, while tli-- manipulations are greatly 

 simplified. There are certain preparations of iron, 

 known as ferric salto, that are not affected in 

 a|i|ie:iiance when certain other chemicals are 

 brought in contact with them : other preparations 

 of iron, known as ferroiu salts, produce highly- 

 coloured pigments when comliined with these same 

 chemicals. 



The action of light ran change ferr/r into ferrow* 

 alt*; hence, if a piece of paper l>e coated with a 

 ferric -alt. dried, and placed under a fern leaf, a 

 piece of lace, or a photographic negative, and ex- 

 posed to light, an image in a ferrous salt is pro- 

 duced wliicli is capalile of being developed into a 

 highly coloured image when acted on by a suitable 

 reagent ; and not only so, but, as this reagent has 

 no action on the ferric salt, they may he mixed 

 together in the first in-iance ami thus applied to 

 tin- paper, when the action of light will develop 

 the highly coloured image, a simple wash in water 

 eonipleiiiig the opeiaiiun. This IK in outline what 

 is known a tin- < 'i/nii'iti//ir in- flhie /iriiitiin/ pro- 

 CM>, lirst published by Sir .1. V. W. Herschel in 

 IH42, which in detail is as follows : 



Two solutions me made up. one containing sixty- 

 four grains of atninonio-ritrate of iron to the ounce 

 of wnter. tin- other forty eight grains of ferricyanidc 

 of |Hpta-sium to the ounce of water. Mix equal 

 quantities of these solutions, and with a soft 

 M|Ninge or flat camel -hnir brush quickly and evenly 



CIIMT one -ide of good smooth while l>a|MT. This 

 is beat clone by gas or candle light ; then place in 

 dry whore it will not be affected l.y daylight. The 



also 

 mere 



paper so prepared is chiefly used for copying plans 

 and drawings on i racing cloth : the tracing, which 

 should lie in a good opaque black ink, is placed 

 on the top of Uie pa|M'r, and both are covered 

 with a glass plate to keep them in |ierfect con 

 tad. Ten minutes in a very bright light will 

 sullice for exposure. The print is now washed, 

 when the lines of the drawing will appear white 

 on a blue ground. The same kind of papei can 

 be exposed lieneath a photographic negative in 

 order to secure a rough proof of toe picture, but in 



this case the tin f exposure is much increased. 



A disadvantage of the almvc process is that the 

 original black drawing on white paper appears as 

 a white drawing on a dark-blue ground. 



The following modification, known as the I 'did 

 process, produces blue prints on white paper : Cum 

 arable, 2T> parts ; common salt, 3 parts ; perchloride 

 of iron, S parts ; tartaric acid, 4 parts ; and water 

 to make up to 100 parts. \\VII -i/ed paper is 

 coated with the above and treated as in the pre- 

 ceding ; it is very sensitive to light. A good 

 tracing in bright sunlight is sufficiently printed in 

 from ten to fifteen seconds. The print developed 

 by immersion in a saturated solution of ferrocyanide 

 of potassium (yellow prussiate), and the de-ign 

 immediately appears in blue. The print is now- 

 rinsed in cold water, and then transferred to a 10 

 per cent, solution of livdrorhloric acid ; another 

 rinse in cold water completes the operation. 



Chrysotyfie. This is a modification of cyanotype, 

 published by Sir J. Herschel. The paper is 

 ly coated with the ferric ammonium citrate, 

 and may be developed after c\|i-uie with a 

 neutral solution of gold chloride, washed with 

 water and dried. The resulting print is in metallic 

 gold in a finely-divided state, ami is of a line purple 

 colour. A dilute solution of nitrate of silver may 

 be substituted for the gold when the image is in 

 metallic silver. 



Kallitype. In this process paper is washed with 

 a strong solution of neutral ferric oxalate. After 

 printing in the usual way, it is developed by the 

 following solution : Nitrate of silver, 50 grains : 

 citrate of pota-h. 800 grains; bichromate of potas- 

 sium, 1 to 2 grains ; rain water, 10 ounces. The 

 piedpiiate formed is next dissolved by the addition 

 of ammonia (strength, -880) about a drachm will 

 lie siillicient . After filtering add 3.1 drops of strong 

 nitric acid, and the developer is ready. This solu- 

 tion is very cheap and easily prepared. The result- 

 ing prints (possess a line rich mack colour. 



PliitiiiiititlH'. in- I'iiitiiiiiin I'fiiifiiiff Proceu. 

 The metal platinum can IK- de|Misited from some 

 of its chemical preparations in an extremely fine 

 black powder when brought in contact with one 

 of the iron salts altered by light. Herschel - \ 

 plained how to get prints in platinum, but the 

 process now employed is that discovered by 

 Willis. Captain Abney, K. U.S., thus describes 

 the chemical action U|MHI which the proc.-s is 

 liaseil : 'Mr W. Willis, jun., found that he could 

 obtain an image in platinum black, by means 

 of development, if he sensitised his paper with 

 ferric oxalate, with which was mixed a solution of 

 chloio plat inii e of potassium. The action of light 

 on this pa pei is to reduce the ferric salt to the 

 ferrous state, and when the ferrous sail is in solu- 

 tion the plai inoiis salt is reduced by it. By lloating 

 the exposed pa|!r on a solution of neutral pot as 

 siiim oxalate, which is a solvent of the ferrous 

 oxalate, the platinum salt in contact with it is 

 immediately reduced to the metallic slate, and an 

 image is thus built up. To fix the prints they are 

 immersed in dilute hydrochloric acid, which dis 

 i way any ferric oxalate tin-re may be, and 

 also gets rid of any oxalate of lime.' 



Paper prepared as above described is supplied com 



