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The photographic news
- Bandzählung
- 6.1862
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- 1862
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 184, March 14, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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M [March 14, 1862. 126 THE PHOTOGRAPHIC NEWS. Tffi Frot Carr on th the 0 in thi other failur by mi affect cattle be dis end: ratus W in that same room where spontaneous drying did not answer. The same collodion has more tendency to wrinkle, when the The injury [he exl in orde The have arran Pany exhibi pany 1 and w desirol &ciene ment < concei eially : stands more f the In will be rative the lin awvarde tion,u motior an exy tion of appara The invite, Buccess Appen save it, owing to its great tenderness when it begins to tear, | particularly when the negative is fixed. The use of citric acid in the developer is important; acetic acid does not sufficiently retard the development unless used in large proportion, and it appears then to make the fill 11 more tender. It gives too red a tone, the tannin itself helpin? that red tint, which is more or less affected by the blue tinge given by the citric acid. A mixture of both acids to develop positives will be found very useful to secure a rich tone. It is also important to have the acid in the silver solution, so that to every drop of nitrate of silver solution added, a sufficient quan tity of acid is sure to be added, and no more when it is neces sary to push on the development of an under-exposed plate by the addition of pyrogallic acid without silver. The development must begin with weak pyrogallic solution, and but little silver, to ascertain what further treatment the negative needs to bring out all the details. With proper expo sure the relative strength of pyrogallic and silver need not bo changed to finish the negative, over-exposure can be re medied by excess of silver, and under-exposure by excess d pyrogallic acid. The latitude given in the exposure of a tannin plate is one of the peculiarities of this process, and a most valuable one. I* is not to say that a good negative can be obtained with a plato much over or under-exposed, but the limits are within the de- gree of appreciation which practice and judgment can give. For instance, supposing five minutes to be the right time for a operations, very difficult to dislodge thoroughly, and which may be the source of spots during development. A good work ing bath, working well with wet process will answer, it should not be too weak, and decidedly acid, sufficiently so to prevent fogging, if too much so the sensitiveness will be affected, but it is preferable to lengthen the exposure and have a clear nega tive to the risk of a foggy one, which is inevitably the case not only with an alkaline bath but even with a neutral one. I have acidified a forty grain silver bath with acetic and with nitric acid, and find either to answer ; one drop of nitric acid for ten ounces of fresh silver bath made of crystallised nitrate of silver, such as is sold by the best dealers, is sufficient. I have not yet found a-collodion giving good results with the wet process, which did not answer with tannin, and I have used collodions giving inferior results wet, with more success after applying tannin; I may say the same respecting the silver bath, having obtained good tannin negatives with an old bath which I found very deficient in intensity with wet process; this is no doubt owing to the great intensity imparted to the film by the application of tannin. Some collodions must be better adapted to the tannin process thanthers, but so many things affect collodion that a formula for a particular one is rarely sufficient to secure the same results, especially if it is kept any length of time. To insure the identity of the two collodions, not only the purity of the chemicals, the preparation of the gun cotton, &c., must be the same, but the temperature itself will effect great changes. In deed, it is one of the great advantages of the tannin over all other dry processes that the particular structure of the collo dion is not of such importance as to prevent good results from being attained with any good negative collodion. I have used old and new, single or mixed, iodides and bromides of ammo nium and cadmium, mixed and unmixed, collodions purchased and containing I do not know what, and have been successful with all. I prefer collodion not too thin, giving a rich creamy film, being a little reddened by age, fine free iodine, and containing a full proportion of bromide, from one-third to two-fifths. The addition of bromide appears essential, great hardness being produced by the use of the iodides alone. I prefer bromide of magnesium or cadmium, readily soluble in alcohol, without addition of water. From fifteen to twenty grains of tannin to the ounce, is a good proportion, more ought to be used if it contained too much resinous matter, which will not dissolve in water. The stronger the tannin solution, the greater the intensity attained rapidly by development, hence with great contrasts it is desirable not to have it too strong to keep the development under better control; but for copying engravings I should think some advantage may be derived by exceeding thirty grains. The solution of tannin need not absolutely be new; I have refiltered a solution one week old, already used, and found no difference in the result. I use it in a vertical bath, dipping the plate in it as I do in the nitrate of silver solution, and moving it up and down and sideways. A twelve ounce solution will do me for twenty four to thirty 7 by 4 stereoscopic plates, and may do for more, provided it is not too much weakened by the water introduced in it with every plate as it comes out of the water. The nitrate of silver must be thoroughly washed off, and the plates never handled without previously wiping the fingers perfectly clean. If it is very warm, and the hand prespiring freely, india-rubber tips for the thumb and middle finger ought to bo used, or spots, while developing, may extend far enough to spoil a negative, will start from the points held. All dust is of course to be avoided as much as possible, and while preparing plates it is desirable not to “ fuss” too much about the labora tory, or disturb anything on the shelves; everything that is needed while the preparation of the plate goes on, ought to be laid in its proper place before beginning. Some operators consider all these precautions as trifling and useless, but nothing in a dry process is too trifling, if there is a good reason for it, and the common occurrence of .persons able to obtain good results with the wet process, and entirely unable to command a dry process, is, I think, mostly owing to this disregard of apparently useless precautions. On taking the plates out of the tannin bath, I wipe the back with a sponge, and stand them on blotting-paper in a box containing one or two hot irons, which I cover, keeping it warm enough to dry a plate in less than from five to six minutes. I have derived much benefit from this drying, and although many, and Mr. Russell amongst them, advise spontaneous drying, I have not The Foreig lam, v will co: monthi All Rlazed [lie sul hack o ho ins Pho I on or i addre been able to obtain as good plates in that way. Tho atmo sphere of some operating rooms may be dry enough, at some seasons of the year, not to require artificial drying, but I find no harm done by it, and much benefit, and therefore would advise it. Plates so dried keep, I believe, somewhat longer. I have been unable to detect any loss of sensitiveness after keep ing them one month, merely enclosed in a mahogany box, and in either negative, as the day was hazy, were not preserved « ! distinct in the negative the most exposed, while the rest wes perfect in both. The nature of a view has much to do with the excess to be preferred, for an excess there must be when the landscape it taken, the different parts of which require very different expo- sure; a sort of compromise must be made, and in every instance it must bo left to the taste of the operator; general rules do no* apply to such cases. Tho operator must decide that point ol tho view which for artistical effect it is most desirable to expose correctly, and weigh tho result for the rest, if too much is sac rificed to that ono part, tho compromise must be made. The strength of the tannin solution will determine whether or not a rapid intensity will be obtained, and the development must bo regulated according to that, and to the subject. Success an 1 ' artistic productions become tho result of a harmony at the com mand of the operator, and the production bears an individuality which sots aside the clamour that photographs are mere me chanical productions. They are certainly nothing else 1,1 many cases, and very poor at that, but a large field is open beyond the mechanical part, and it remains for photographer^ to enlarge it more and more, so as to establish photography 118 truly a fine art. A dry process giving as good results as tho wet is certain') preferable for field work. The tannin I do not hesitate to Sa) gives better results; the smoothness of the film insures better definition, which is not objectionable in the least, not withstand, ing all that has been said against sharpness, and when every thing is not sacrificed to it. To substitute an exposure of five seconds to five minutes 1n a landscape is no object. Five seconds is entirely too long, an a view which need not be taken in much less time, can just “ well bo taken in five minutes. Neither exposure will sec™r moving objects, and if any happen to pass, what will bo a bi 1 he same collodion has more tendency to wrinkle, when to instan plate is plunged in water, if it is done within two or three days I group after it is prepared than if kept a little longer. To prevent the very water from getting under the film I have used negative varnish, I Ib rather thick, applied on tho edges after exposure; I find it to be c answer very well. Any ono who has experimented with tannin short plates, must know that, although they will stand much wash ing when the film is well secured, it is almost impossible to particular view, four to six minutes’ exposure will give a very good negative of the same view. This I have tried conclu- sively, and went as far as doubling the time, and all th and a difference was, that distant hills, miles away, not well define!
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