Some of our oldest and most successful operators still adhere to and prefer the iodized paper prepared by the double process, which certainly effects a saving in the use of the iodide of potassium. The following is the easiest way of so preparing it:—Having floated your marked surface of the paper on a 30-grain solution of nitrate of silver, and dried it[[4]], immerse it for 20 minutes in a solution of iodide of potassium of 20 grains to the ounce, when it immediately assumes the desired colour. It is then requisite, however, that it should undergo the same washing in pure water as the paper prepared by the single process.
Upon the goodness of your iodized paper of course depends your future success. Although it is not requisite to prepare it by candle-light (which in fact is objectionable from your inability to see if the yellow tint is equally produced), I think it should not be exposed to too strong a light; and as the fly-fisher in the dull winter months prepares his flies ready for the approaching spring, so may the photographer in the dull weather which now prevails, with much advantage prepare his stock of iodized paper ready for the approach of fine weather.[[5]]
Many other ways of iodizing paper have been recommended which have proved successful in different hands. Dr. Mansell, of Guernsey, pours the iodide solution upon his paper, which previously has had all its edges turned up so as to resemble a dish; he rapidly pours it off again after it has completely covered the paper, and then washes it in three waters for only ten minutes in all: he considers that thereby none of the size of the paper is removed, and a more favourable action is obtained. In the experiments I have tried with the use of the air-pump, as recommended by Mr. Stewart, I have met with much trouble and little success; and I am inclined to attribute the very beautiful specimens which he has produced to his own good manipulation under a favourable climate.[[6]]
To excite the paper take 10 drops (minims) of solution of aceto-nitrate of silver, and 10 drops of saturated solution of gallic acid, mixed with 3 drachms of distilled water.
The aceto-nitrate solution consists of—
| Nitrate of silver | 30 | grains. |
| Glacial acetic acid | 1 | drachm. |
| Distilled water[[7]] | 1 | ounce. |
If the weather is warm, 6 drops of gallic acid to the 10 of aceto-nitrate will suffice, and enable the prepared excited paper to be kept longer.
This exciting fluid may be applied either directly
by means of the glass rod, or by floating, as before, and then the glass rod. But if floating is resorted to, then a larger quantity must be prepared. As soon as it is applied the paper should be blotted off by means of blotting-paper (which should never be used more than once in this way, although preserved for other purposes), and put into the dark frames for use.[[8]] It is not requisite that the paper should be perfectly dry. This exciting should be conducted by a very feeble light; the paper is much more sensitive than is generally supposed; in fact, it is then in a state to print from by the aid of gas or the light of a common lamp, and very agreeable positives are so produced by this negative mode of printing.
I would advise the aceto-nitrate of silver and the solution of gallic acid to be kept in two bottles with wooden cases differing in their shape, so that they may not be mistaken when operating, in comparative darkness. A ¼ of an ounce of gallic acid put into such a 3-ounce bottle, and quite filled up with distilled water as often as any is used, will serve a very long time.