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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- http://digital.slub-dresden.de/id1780948042-18850000
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- Bandzählung
- No. 1388, April 10, 1885
- Digitalisat
- SLUB Dresden
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- Ausgabe
- Parlamentsperiode
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Zeitschrift
The photographic news
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Band
Band 29.1885
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- Register Index III
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Band
Band 29.1885
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- Titel
- The photographic news
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April 10, 1885.] THE photographic news. 231 I find one thickness of the paper supplied by most stock dealers perfectly safe ; it is a good plan to have a thick plate of glass outside to keep inquisitive people from push ing a hole through the paper. I mention this through losing over nine dozen 5 by 8 plates from the attempt of a friend to rear himself up inside my dark room. Almost any developer is good for these plates, but I prefer, for out-door work, ferrous oxalate iron solution, one to four of oxalate solution. THE PLATINOTYPE PROCESS. BY BICHARD KEENE.* At the request of our Committee I have arranged to give you a demonstration of platinotype work at my rooms for the sake of convenience in manipulation ; and I hope that this our first technical meeting may soon be followed by others of a similar nature, where our members may learn more in seeing the modus operandi of any process than by much longer study and unaided practice. The invention or discovery of the platinotype process, in 1878, is due to Mr. Willis, and is a patent, but as the terms for work ing it are so extremely moderate, it comes within the reach of all. Great improvements, too, have more recently been introduced, and it now stands as one of the simplest and best of photographic processes—quick and clean in working, artistic in its results, and, beyond all other excellencies, absolutely permanent. This latter quality, the purity of the high lights in the picture, and the capability of printing with a white margin, added to its mezzo - tint-like appearance, all render platinotype the very best method of illustrating books where moderate numbers are required, such as topographical works or the journals of our various antiquarian societies. In proof of this, I lay before you some of the works I have had the pleasure of illustrating. Here is one With only a frontispiece, of which 2,000 have been printed ; hero 18 another with twelve illustrations, of which 750 have been published. Now, to have engraved these plates would have cost a large sum, not less than from £12 to £15 each, and it is a question if they would have been as good ; they certainly would not have been so faithful. Besides this outlay comes the cost of printing from the plates, so that you will see what a boon this new process is, and will become, to authors and publishers of county histories and such like works. Look at this large fourth book, a local history of a little place many of you, 1 dare say, never heard of. Only 120 copies were printed. What would it have cost to engrave all these illustrations '! Why, the book would never have been printed, or, at all events, would not have possessed half the charm it now does. You will see, too, how well the colour of the platinotype harmonizes with the accom panying type, and—though comparisons are odious—I will say better than that of any other process, for there is no enamelled surface, no meretricious glazing, but a simple black and white, highly artistic picture, such as can be produced by no other method. Please take this as my honest opinion. I know, with many, nothing can equal the charm of the warm chestnut-brown, the rich purple, or other tones which may be given to a silver print—but alas ! it fades. I have printed some specimens fiom the same negative in both ways, so that you may compare the two; but whatever your present judgment may be, I feel sure it would alter in the future even as surely as will the silver prints. Now let us see what this platinotype consists of, without going very deeply into the matter, as you will have to procure the ready sensitized paper from the Company, according to the terms of license. A per-salt of iron (ferric oxalate) is inti mately mixed with a salt of platinum (potassic-chloro-platinite), and a sheet of suitable paper is evenly coated with the mixture. When properly dried and exposed to light behind a negative, the ferric salt only is affected or acted upon, according to the grada tions of light and shade in such negative, yielding a faint dusky- grey image of ferrous oxalate. The action of light through the negative has reduced the ferric into the ferrous salt, and the ferrous salt will, in its turn, be the reducer of the platinum ; but not so long as the print is kept dry. If, however, this print be now floated on a hot solution of potassic oxalate, the ferrous oxalate will be dissolved at once, and at the same instant the contiguous platinum salt will be decomposed or reduced, thus forming the image in pure precipitated platinum, one of the most stable and unalterable substances known. On cooling, the » Bead before the Derby Photographic Society. developer will show green crystals, formed by the combination of the ferric oxalate with the potassic oxalate, as you can see in this Winchester, where I store my bath when not in use, and from which I now decant the clear solution into this enamelled iron dish. The crystals remaining are useless, and are removed from time to time. I put the dish on a tripod, add a fresh sup ply of potassic oxalate dissolved in water (130 grains to the ounce), to keep up the normal strength, and apply a Bunsen burner till the bath is heated to 160° or 170°. In this tin case are some prints ready for developing, several of them purposely under or over-printed. On comparing them with those properly timed, you will see the difference; but after floating on the developer, it will of course be more apparent. With these other prints similarly under and over-printed, I hope to show how they may be saved by raising or lowering the temperature of the bath. The prints, as they are developed, are immersed in a dilute bath of hydrochloric acid (1 to 80), for about ten minutes ; they are then removed one by one to another such bath ; and if there are many prints in the batch, to a third, till all trace of yellowness has disappeared. This insures the purity of the whites. Half an hour’s washing under the tap completes the operation, and the prints only want drying off in changes of blotting-paper. A little practice is required to know how far to carry the print ing, and only experience can point this out. I have never used an actinometer for the purpose, but prefer to fix upon some ob ject of medium density in the negative, and work from that alone. By doing this I rarely spoil more than one print, and often hit the time at once, which is about one-third of that required for a silver print. As the paper varies somewhat in different batches, it is well to try a sample print before printing the full number for development, even though working from the same negatives. Experience points to plucky negatives for the best results ; this you will find borne out by examining the pre sent negatives and their respective prints, though some of the weaker negatives have yielded pictures of great softness and delicacy. Last, but not least, I must impress upon you the great importance of keeping this very sensitive paper from light and damp. Perfect dryness at every stage is indispensable. These tin cylinders, as you see, are made as nearly air-tight as possible, with the addition of an india-rubber band. There is a perforated box inside each, filled with dry calcium chloride, which absorbs any little moisture which may get in. This cal cium chloride is dried from time to time over the fire in an iron dust-pan. India-rubber sheets, or oiled silk, are recommended as pads for the printing-frames : I found them inconvenient to handle, and prefer dry blotting-paper, a stock of which is kept ready for use on printing days, on a heated iron table in the changing-room. Each print, as it comes in from the printer, is put in one of these tin tubes, and there kept bone dry till wanted for development. I do not want to lead you to imagine that there is any real difficulty about keeping the paper dry, or to frighten you about its keeping qualities. It only requires ordinary care, and you can preserve it as well in winter as in summer ; indeed, I do not know if there is not more danger of deterioration in summer, for heat is often accompanied by a great amount of moisture, and the two together is worst of all. I have done some of my best work in frosty weather, and to show you what can be done, here is a print from an intensely dense negative by an amateur, which took three full days to print in the damp, dark days of December! I have read of some one who got good prints from paper he had kept two years, but I should not recommend you to try this. It may seem that I have been demonstrating backwards, but I have pursued the plan I thought best calculated to fix what I had to show and say on your memories. I have said nothing about the sepia-tinted platinotypesof which you see some among the numerous specimens submitted to you. For these you require a somewhat different paper, deeper printing, and a hotter developing bath, to which is added 130 grains of the Special Solution, supplied by the company, to each ounce. The sepia paper does not keep so well, and is a little more difficult in the working. There is another and still newer branch of platinotype work— enlarging by the electric light. Mr. Willis has lent me the specimens on the screen ; they appear to be eminently adapted for colouring or finishing in monochrome ; there is no degradation of the whites, and you will notice the vignetting is clear and pure as possible ; no chemical action takes place to affect the artist’s colours, and the surface of the paper is agreeable to work upon.
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