SPECIAL PRINTING PROCESSES 497 



It does not, it is true, admit of the use of the more beautiful paper supports, but on the 

 other hand it is far more flexible than platinum in the matter of local modifications. 

 The finest expression of the process is secured by printing as lightly as possible, using 

 relatively cool water for soaking — sometimes as low as 86 or even 84°F. — and develop- 

 ing slowly and gently, pouring the sawdust easily and lightly with no violence what- 

 ever. This technique means slow development — the writer not infrequently spends 

 an hour or more in developing an 8- by 10-in. print — but the result amply repays the 

 trouble involved if the worker cares for exquisite print qualit3^ 



Oil and Bromoil Printing and Transfer. — Oil printing depends on two facts: (1) 

 when a bichromated gelatin film is exposed to light, it becomes more or less tanned in 

 proportion to the amount of light action; and (2) if this film is soaked in water, it 

 absorbs water and becomes repellent to an oily ink in inverse proportion to the amount 

 of light action. In bromoil — which is an outgrowth of oil, exactly as carbro is an out- 

 growth of carbon- — the tanning action takes place as a result of the chemical reaction 

 between a special sensitizer (ordinarily called the "bleacher") and the silver image of a 

 bromide print or enlargement. After the sensitizing, drying, and printing in the case 

 of oil or the bleaching, fixing, and washing in the case of bromoil, the print is soaked 

 until the gelatin is properly swelled; it is then surface-dried. A suitable ink is dabbed 

 on with a special brush until a sufficient amount has adhered to the print to give 

 the desired image, when the print is pinned up to dry and may be considered finished. 

 Or, if desired, the print, may be placed in contact with a piece of plain paper while the 

 ink is still soft, and may be run through a press similar to an etching press, in which 

 case the ink is transferred to the plain paper, giving an effect quite different from that 

 of the original print. After such transferring, the print may be soaked and inked a 

 second, third, or fourth time, or even oftener, and these inkings may either be trans- 

 ferred to different pieces of paper or may be transferred to the first one, thus producing 

 a multiple print. Since there is great latitude not only in the matter of the original oil 

 or bromide print but also in the matters of soaking, choice of inks, and manner of 

 applying the ink, the oil and bromoil processes are exceedingly flexible, almost equal- 

 ing multiple gum in this respect. 



As will be seen from the above, the oil process is a contact medium requiring a 

 strong light for printing, whereas the bromoil process makes it possible to produce 

 large prints without the need for an enlarged negative. Other than this, they are 

 practically if not entirely identical in the results obtainable. It is true that one 

 author claims that bromoil gives a longer scale of gradation than oil, but the present 

 writer has not found this to be the case and believes that the error is due to the fact 

 that the special paper which is supplied for oil printing is thinly coated with gelatin. 

 If a sheet of bromide paper of a type suitable for bromoil is fixed without exposure to 

 light, washed, sensitized, printed, and soaked, it gives as long a scale as though it were 

 used by the bromoil process. 



Advantages. — If the proper paper and inks are used, the prints are absolutely 

 permanent. 



The process is extremely flexible, in respect to both modifications of total contrast 

 and local modifications of values. 



A verj'^ beautiful quality of richness and depth in the shadows is possible. 



By varying the thickness of the ink, the mode of handling the brush, or both, very 

 delightful variations in texture may be secured. This characteristic is even more 

 apparent when transfer is vised, since a final support of almost any desired character 

 may be used. 



Very wide variations in color are possible through choice of inks. 



Multiple prints are readily made by transfer, this making possible still greater 

 modifications of total contrast and of local values. 



