494 HANDBOOK OF PHOTOGRAPHY 



black, dark brown, sepia, blue-green, green-blue, and red and on either a white or 

 cream support, which last may be either smooth or slightly rough. 



As the emulsion is very delicate and as the warmth of the fingers is sufficient to 

 melt the colloid, it is advisable to handle the paper only by the edges; therefore it 

 should be purchased and used a size larger than the print is to be i.e., 5 by 7 in. for a 

 4- by 5-in. print, or 11 by 14 in. for an 8- by 10-in. print. If larger prints are wanted, 

 it is best to get the full-size sheet, approximately 23 by 35 in. and cut it to size. 



The Sawdust.- — This is a special boxwood sawdust, put up by the manufacturers of 

 the paper and sold in packages of the proper amount to make 5 or 6 qt. of the soup. 

 The exact amount of water is not important; the soup should be thin enough to pour 

 readily but not so thin as to be ineffective, and wathin these wide limits the strength 

 does not greatly matter. 



The sawdust may be used repeatedly — almost indefinitely, in fact^ — and does not 

 lose its effectiveness. It is simply allowed to dry between the occasions of use, being 

 mixed again with water when desired. It is sometimes stated that a preservative 

 should be used in the soup to prevent putrefaction of the gelatin which is washed off 

 the prints; but the writer has not found this to be at all necessary, having used the 

 same batch of sawdust for more than 4 years with no trouble whatever. It is true 

 that the gelatin forms a hard crust over the sawdust as the water evaporates, but this 

 does no harm, being readily soaked soft again. 



The Sensitizer. — This is normally a 1 per cent solution of potassium bichromate, 

 made up as follows : 



Water 1000.0 cc. 30 oz. 



Potassium bichromate 10 . g. 144 gr. 



This keeps indefinitely if protected from light and may be used repeatedly. 



Different strengths of sensitizer may be used for different purposes, as will be 

 discussed under Variations in Contrast. 



Sensitizing.- — ^The potassium bichromate solution is poured into a clean tray to a 

 depth of }i in. or more, and the sheet of Fresson paper is slid into it, the edges being 

 pressed down as they curl up, any adhering air bubbles being broken by a light touch 

 of the fingertip or of a soft brush, and the tray being rocked. At the expiration of 

 4 min. from the first immersion, the paper is lifted from the sensitizer and is hung up 

 to dry in the dark; clips are used at the corners. It is advisable to hang it cornerwise, 

 so that the sensitizer will drain from one corner. 



Sensitizing may be done in any ordinary room, as the paper is not sensitive until 

 dry; it should, however, be dried in the dark, since when dry it is slightly more sensi- 

 tive than a printing-out paper. 



The sensitized paper will dry, in proper conditions of humidity, in a very short 

 time — drying may be hastened by an electric fan- — and the paper should be used as 

 soon as possible, since when dry it tends to become insoluble without exposure to 

 light. Even if kept in a sealed tin with preservative, as is done with platinum paper, 

 it will not keep in good condition for more than a few days. 



The sensitizer should be used at a temperature of between 65 and 75°F.; if too 

 warm, it will soften the gelatin of the paper excessively. 



If the paper is allowed to become bone dry while hanging up, it will curl very 

 badly. It is therefore advisable to take it down when it is dry enough not to stick to 

 anything and then to finish drying under light pressure. This is not, however, 

 absolutely necessary, as with care, the paper can be handled even when badly curled. 



Printing. — This requires a strong light, such as is used for platinum or carbon, and 

 no precise directions can be given as to time, as this varies with the negative, the 

 color of the tissue, the possible moisture content of the colloid film, and the effect 



