The more simple a collodion is the better; and the following, from its little varying and active qualities, I believe to be equal to any now in use.
A great deal has also been said upon the preparation of the simple collodion, and that some samples, however good apparently, never sensitize in a satisfactory manner. I have not experienced this difficulty myself, or any appreciable variation.
The collodion made from the Swedish filtering paper, or the papier Joseph, is preferable, from the much greater care with which it is used.
If slips of either of these papers be carefully and completely immersed for four hours in a mixture of an equal part (by weight) of strong nitric acid or nitrous acid (the aqua fortis of commerce) and strong sulphuric acid, then perfectly washed, so as to get entirely rid of the acids, the result will be an entirely soluble material. About 100 grains of dry paper to a pint (twenty ounces) of ether will form a collodion of the desired consistence for photographic purposes. If too thick, it may be reduced by pure ether or alcohol. However carefully this soluble paper or the gun cotton is prepared, it is liable to decompose even when kept with care. I would therefore advise it to be mixed with the ether soon after preparation, as the simple collodion keeps exceedingly well. Excellent simple collodion is to be procured now at the reasonable price of eight shillings the pint, which will to many be more satisfactory than trusting to their own operations.
To make the sensitizing Fluid.—Put into a clean stoppered bottle, holding more than the quantity required so as to allow of free shaking, six drachms of iodide of potassium and one drachm of bromide of potassium; wet them with one drachm of distilled water first, then pour into the bottle ten ounces of spirits of wine (not alcohol); shake frequently until dissolved. After some hours, if the solution has not taken place, add a few more drops of water, the salts being highly soluble in water, though sparingly so in rectified spirits; but care must be taken not to add too much, as it prevents the subsequent adhesion of the collodion film to the glass.
A drachm and a half to two drachms, according to the degree of intensity desired, added to the ounce of the above collodion, which should have remained a few days to settle before sensitizing, I find to act most satisfactorily; in fine weather it is instantaneous, being, after a good shake, fit for immediate use. If the sensitive collodion soon assumes a reddish colour, it is improved by the addition of one or two drops of a saturated solution of cyanide of potassium; but great care must be used, as this salt is very active.
Hugh W. Diamond.
Replies to Minor Queries.
Portrait of Alva (Vol. ix., p. 76.).—There is a fine portrait of the Duke of Alva in the Royal Museum at Amsterdam, by D. Barendz (No. 14. in the Catalogue of 1848); and Mr. Warden will find a spirited etching of him, decorated with the Order of the Golden Fleece, in the Historia Belgica of Meteranus (folio, 1597), at p. 63. The latter portrait is very Quixotic in aspect at the first glance, but the expression becomes more Satanic as the eye rests on it.