Volltext Seite (XML)
January 30, 1863.] THE PHOTOGRAPHIC NEWS. 51 Norris’s plates ; twenty by the waxed paper process, all these being by French contributors; sixteen by various carbon and photolithographic processes ; five by the Fother gill process; four by the tannin and malt process; two simply described as dry collodion; two by the honey pro cess ; two by the collodio-albumen and honey process ; two by the metagelatine process : two by Corbin’s collodionized paper process ; one by the morphine dry process ; one by the albumen process; and half a dozen daguerreotypes. The number's of course refer to contributions or frames, which in many cases include several pictures. It is a somewhat singular fact, that whilst dry collodion processes have occu pied so large a share of public attention, they are so meagerly represented here. In excellence, however, the dry processes present a more satisfactory result; some of the best pictures in the exhibition having been produced by the collodio- albumen and tannin processes, and their modifications. The Fothergill process puts in a very poor appearance this year ; of the small number of contributions the majority being very poor indeed. The process has evidently been declining in popularity, and the results here exhibited will not be likely to give it a fresh impetus. PRINTING DIFFICULTIES. BY A PHOTOGRAPIER’s ASSISTANT. The advantages derived from the method described, for separating a portion of the chlorine from the gold, cannot be too highly estimated, as it gives us entire control over the bleaching power necessary to be exercised in toning opera tions ; by the addition of soda in excess, the same results may be obtained; but, beyond a certain point, our controlling in fluence is lost, or at least uncertain in its operations. To those who have not made the science of chemistry their study, it may appear strange that the application of heat, whilst separating a portion of the chlorine, leaves the solution in a condition as acid as before, thus rendering necessary the same quantity of soda to produce an alkaline reaction; for the information of this class of inquirers, I shall endeavour toexP lain the reason why the separation of chlorine has no influence on the acid introduced with the gold into the toning solution. . I he chloride of gold usually sold for toning purposes, is made by dissolving a portion of the metal in a mixture of nitric with hydrochloric acids, or what is termed aqua regia: from the hydrochloric acid it derives its three equivalents of chlorine, so that, when separated by evaporation, it exists as a terchloride plus free acid in un certain quantities ; and this acid, which is a mixture of chlorine, hydrogen, nitrogen ami oxygen, we have reason to believe, separates itself from the chloride of gold immediately it is brought into contact with water; so that the heat, whilst exercising its decomposing influence upon the chlorine in combination with the gold, leaves unmolested the free acid, be its quantity great or small; consequently the same proportion of soda is required to produce alkalinity as would be required with the gold when in combination with its full amount of chlorine. Strictly speaking, the presence of soda with the terchloride is unneeded, whilst this last- named substance is undergoing the process of evaporation. But I am inclined to think that the presence of a small por tion of soda hastens decomposition, not by its combination with the liberated chlorine, but by combining with the free acid it prevents the gold obtaining a fresh supply of chlorine from this source; so that, when a toning bath is to be used directly, it would, doubtless, be an advantage to add a huger quantity of soda than I have before named, the quantity being regulated by the amount of reduction re- xuIred ' but in no case where heat has been applied should t ie so u mn be strictly alkaline; for, except a trace of the stronger oi the.more faintly marked liberated carbonic acid be present, toning action will proceed but slowly indeed. It s iou < ever be remembered, that the presence of an aci< increases the bleaching power possessed by the toning solutions, and here I would suggest, thatthisapplicationofheat be resorted to for the purpose of giving the necessary qualities to the toning solutions hitherto considered unfit for use, until they have undergone a term of probation in peniten tial solitude upon some dusty shelf (not making use of those fanciful solutions, I merely give this hint on theo retical grounds). Before proceeding with the details of my recent experi ments, I would just observe, that I shall have occasion to offer remarks that may lay me open to the charge of inconsistency, they being somewhat at variance with the teachings contained in my letters recently published; but, be it remembered, I have been, and still am follow ing, an almost unbeaten track; and, as I grope my way, I heed not the stones behind, though they for a time have supported my faltering steps, fixing my eyes steadily upon the goal of entire, undoubted knowledge of the sub ject, and throwing aside theories, useless as they are lum- bersome; after their work is accomplished, stepping from stone to stone, I move slowly forward, at the same time giving the photographic world the benefit of the faint gleams of light that have dawned upon my mind ; and as the amount of light increases, I bring my increase of know ledge (if increase it be), and humbly add it to the stock of information contained in that best of photographers’ hives, viz., the Photographic News. And now, without further remarks, I proceed to tone the prints described in the former portion of this paper: for, by this time, the solution is cold — or, at least, lukewarm — a condition most suitable for the present season of the year. Pouring this solution into the por celain dish, for the sake of further tests, an addition of soda was made from time to time, commencing with half a grain, which, of course, left the solution still in an acid con dition. The prints, which had been all printed the usual depth, viz., a full allowance made for reduction, I now commenced exposing to the action of the toning bath. No. 1, short floating, on sensitizing solution, became faint and slaty, with mealiness, though in a greatly modified form. No. 1, long floating, on ditto, retained a large por tion of vigour, but still a faint trace of the same description of mealiness. The other prints followed in succession; those floating upon the strongest bath, though reduced rapidly, gave no trace of the disease until the slatiness began to appear. I now added another half a grain of soda to the bath. The reduction was not so rapid, but dark tones could not be obtained until mealiness in somewhat the same form made its appearance in the light background of the pic tures ; and now another half a grain was added—making in all three grains of carbonate (not bi-carbonate, remember) of soda to the grain of gold; the prints now toned more slowly, increasing rather than diminishing in vigour; those floated on the strong solution giving the most satisfactory results, although, for want of the strong bleaching power, all retained their over-printed appearance. This was just what I was in search of, a process that would give vigorous prints without any over-printing. (To be continued.) RESEARCHES IN HELIOCHROMY. BY M. NIEPCE DE SAINT VICTOR. FIFTH MEMOIR—CHAPTER . On the Reproduction of Colours in Heliochromy. I now state the results of the observations I have made during the past year, and, although the summer has not been favourable to my experiments with the camera obscura, still I have been able to obtain some proofs. 'The obtaining of colours in the camera obscura best shows what heliochromy can give us ; for here there can be no illusion, heliochromy cannot reproduce everything; but, nevertheless, it can give us many things; and thus it is
