372 



NOTES AND QUERIES. 



[No. 155. 



ounce of distilled water. This, with a little prac- 

 tice, will be readily effected. As soon as the 

 surface has become dry, immerse the paper in a 

 solution of iodide of potassium — twenty grains to 

 the ounce of water, when it will soon assume a 

 pale straw colour, in consequence of the deposit 

 of the iodide of silver on its surface. After two or 

 three minutes' soaking, remove it, and float it care- 

 fully into another vessel of clean water, where it 

 should remain an hour or more. By some it is 

 recommended to change the water, and repeat the 

 soaking, so as to remove all salts except the in- 

 soluble iodide of silver. When this is done, pin 

 the paper up by one corner to a tape suspended 

 across the room, or to any other convenient place, 

 until it is perfectly dry, when it is ready for the 

 next operation. As this iodized paper is not de- 

 teriorated by time, it may be made in any quantity 

 and kept for use. 



The next process is to excite the paper ; and 

 this, which must be done in a dark room, by the 

 light of a candle, is as follows. Apply evenly and 

 smoothly, and without hesitation, as much of the 

 following preparation as is required to cover per- 

 fectly the whole of the iodized surface, which is 

 to be then immediately dried off by means of 

 blotting-paper : 



Aceto-nitrate of silver - - 20 drops. 

 Saturated solution of gallic acid - 20 „ 

 Water 120 „ 



The aceto-nitrate of silver consists of 



Nitrate of silver - - - 20 grains. 



Water - - - - - 1 ounce. 

 Acetic acid - - - - i drachm. 



The negatives which it is intended to print 

 being placed in the pressure-frame, with the var- 

 nished collodion side upwards, the paper which 

 has been excited (as just described) is laid upon the 

 picture, and brought into close contact with it by 

 pressure. The frame is then removed into the 

 light, and an ordinary glass negative will in general 

 be sufficiently printed off after an exposure to day- 

 light, not sun-light, in four seconds. From two to 

 three minutes will be required from the light of 

 a small gas burner, and the object should be 

 placed within a foot of the light. 



After this exposure, the paper being removed 

 from the pressure- frame, again in a darkened 

 chamber, and held as before in the left hand on a 

 piece of board, the picture is developed by the 

 application of a mixture of equal parts of a satu- 

 rated solution of gallic acid, and the undiluted 

 aceto-nitrate of silver. 



If the picture has been exposed a sufficient time, 

 a very faint image should be perceptible ; if it has 

 been too strongly exposed, the image will imme- 

 diately appear, and the after-picture will, it is 

 probable, have an unpleasant red colour; which 



may in some degree be diminished by using nn 

 excess of gallic acid, or even developing by gallic 

 acid alone. Should the picture be tardy in its de- 

 velopment, it may be much accelerated by gently 

 breathing upon. 



The picture is then to be washed by pouring 

 water on its surface, and allowing it to remain in 

 clear water for an hour or so : and to be fixed by 

 soaking it in a solution of hyposulphite of soda, 

 half an ounce to eight ounces of water. The entire 

 removal of the yellow iodide will indicate the suf- 

 ficient application of the hyposulphite. It is then 

 to be again immersed in clean water for an hour 

 or so, to wash out the hyposulphite of soda ; and 

 the tone of the picture is often greatly improved 

 by passing a warm iron over it. 



The following is another mode of printing, and 

 one which, when a good light can be obtained, I 

 have found succeed very perfectly ; while it has 

 to some this strong recommendation, that it is 

 more easily managed than the former process. 

 For this, the French paper of Canson's make is the 

 best. The paper is first salted by immersing it in 

 a solution of muriate of ammonia, one grain to ihe 

 ounce of water, for twenty minutes, and then 

 hung to dry. When dried, it may be kept ready 

 for use. 



To excite this paper, apply in the same way 

 as in the former a solution of ammonio-nitrate 

 of silver, which is formed by dropping into a 

 solution of nitrate of silver of thirty grains 

 to the ounce of distilled water, very carefully, 

 strong liquor ammonise. At first the solution 

 becomes very turbid, and has a dusky brown ap- 

 pearance ; but upon more of the liquor ammonise 

 being dropped in it, is again rendered transparent. 

 There should be no excess of ammonia, and the 

 fluid should have a slight smell similar to tar. 

 This solution is to be applied to the paper either 

 by a brush, or a glass rod ; and to be dried off by 

 blotting-paper, as in the former process. 



The time of exposure to obtain a picture by this 

 mode must be much longer than in the former — 

 a quarter of an hour will in general not be found 

 too long ; and it is well to overprint, and produce 

 a much darker picture than is desired, because the 

 hyposulphite of soda into which it is now to be 

 immersed, as in the former process, generally re- 

 duces the intensity of the shadows very con- 

 siderably. 



The tints of pictures taken by this process may 

 be varied, and a very agreeable sepia colour pro- 

 duced by using muriate of barytes in the first 

 instance, in the same manner and in the same pro- 

 portion as the muriate of ammonia. 



Beginners often find themselves in a difficulty^ 

 from not knowing which is the proper side of the 

 paper to receive the picture. This may always 

 be avoided by selecting the upper side, when the 

 water-mark reads from left to right; but when 



