Camera Craft

Otago Witness, Issue 3860, 6 March 1928, Page 60

Camera Craft

a leature of Ametaure PHOTOGRAPHERS

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View Finder.

[ Readers of the Otago Witness are invited to submit specimens of their work, and, if they desire it, to seek advice from “ View Finder.” Questions trill be ansivered only in these columns and written replies cannot be sent.]

INTENSIFICATION BY REDEVELOPMENT.

fixing, and tabloids for every process, which lequire nothing more than the addition of water. Still, there are some who like to make up their own solutions; and there is a good deal to be said for the practice, if it is indulged in moderation. One of the rules to remember is that the order in which the ingredients ai e named in a formula is the order in which they should be dissolved in water, which itself is generally stated last. With a great many of the solutions which are used in photography this order docs not matter at all; but with some it is very important. Therefore, unless one knows definitely that in a particular case the order does not matter, the rule should be adhered to.

Under-exposure will always give negatives too dense in the high lights and with insufficient detail in the shadows. Many methods of intensification only tend to aggravate the undesirable condition and increase the contrast. The following method will be found to give excellent results. The negative, after being developed, fixed, washed, and dried, is placed in water for half an hour. It is then transferred to the following bleacher: — Water 150 c.c. Potassium bichromate 6.5 grams Potassium bromide 1.5 grams Nitric acid pure 25min During immersion in the bleacher the dish is gently rocked. After a short period the image practically disappeais, only a bas relief effect (caused by the swollen gelatine) being seen. The negative is next thoroughly washed in running water and removed to a 5 per cent, solution of metabisulphite of potash. The plate is allowed to remain in this bath for 10 minutes, and is again well washed. The plate is now redeveloped in daylight with any ordinary developer, but the developer should not contain bromide. A good developer, giving excellent black tones, is amidol, prepared as follows: — Amidol • GOgrs Sodium sulphite loz Water to 20oz A thorough washing completes the process. Fixation is not necessary. AMMONIUM PERSULPHATE AS A NEGATIVE REDUCER. Harshness due to over-exposure and full development is a fault which is more rare than that of under-exposure. No matter how careful a photographer is, it will occur at some period, and often the negative is a valuable one, or one not easily replaced. The subject may be harsh in character, or it may be difficult to give sufficient exposure to secure softness. In such cases as these the value of such a reducer as ammonium persulphate is felt. The following formula and method of working will give excellent results. It must be borne in mind that ammonium persulphate is a reducer which works ■ very rapidly. If the photographer has not used it before, it is a good idea to try it first on an old negative, the speed of reduction can thereby be judged. Prepare a stock solution as follows: — Ammonium persulphate loz Sodium sulphite 90grs Sulphuric acid . 45min Water to 9 joz The strength of the ammonium persulphate in this solution is 10 per cent, and the solution has good keepiim qualities if kept in well-stoppered bottled lor use the solution requires diluting, the dilution varying with the plate. Some plates will only require one part of the stack solution and nine parts of water, this solution then being equal to a 1 per cent, solution of ammonium persulphate. If the gelatine of the negative is hard a stronger solution than 1 per cent will be required. In some cases a 2 per cent, or 2J per cent, solution may be necessary, but it is advisable to use the weaker strength if possible. In some cases the negative does not respond to treatment, no reduction taking place. Where difficulty is experienced the negative may be immersed for a few minutes in a dilute ammonia bath, consisting of one part of strong ammonia to 100 parts of water After immersion in this bath the negative must be well washed. In any case the negative is to be soaked n water before reducing. To reduce density the negative is immersed in the diluted persulphate solution and the dish rocked. Soon after the negative is placed in the solution a milkiness is seen flowing from the denser portions, this bein« an indication that the solution is°working satisfactorily. The action is continued until it is removed from the solution, washed rapidly in two changes of water and placed in a plain solution of hypo or an ordinary fixing bath for about 10 munites. It is then well washed and dried in the usual manner. MAKING SOLUTIONS: SOME GENERAL HINTS. A LESSON FOR BEGINNERS. Weights and measures, and formulae, have been deal with in the last two “ Lessons."' This week I propose to sav something about making up photographic solutions in general. , Not that the beginner need do much of it unless he likes. Manufacturers and dealers have conspired to make his path smooth, and he can buy concentrated developer, packets of chemicals for toning and for

Moreover, it should bo carried out, not merely by di opping the solids into the water in the order named, but by taking care that one is dissolved before the next is added. When the order of addition matters, it is, of course, the order in which each passes into solution which is important. It may be objected that this makes the compounding of a solution a very long job, but if the advice which I shall give is taken, this will not be so. —“ Water To.”—When a formula states “ water to ” such and such a quantity, it means that the total bulk of the solution when made up should be the quantity indicated. In order to get this, the water used for disolving should be a little less than the total measurement of the solution, because the solids added to it increase its bulk. We therefore, when we are measuring the water, leave an ample margin for the solids; and then, when everything is dissolved, the solution is put into a measure and water added until it has the bulk given in the formula. —Distilled Water Unnecessary.—

Some photographic formulae specify “ distilled water,” but this is quite a needless refinement. The purer the water the better, naturally, as with impure water there is always the possibility of the presence of something undesirable. But for none of the ordinary photographic processes is anything purer than the house supply of drinking water necessary. In fact, the “impurity” which is’ most likely to give trouble is generally present in distilled water—l mean dissolved air.

Photographic developers deteriorate from what.is known as “oxidation,” and this is very largely due to the oxygen in the air which is to be found dissolved in.water. If the water is allowed to boil briskly for three or four minutes this air is driven off, and if such water is left to get cool or cold undisturbed, it will not dissolve much air again in an hour or two. °

Anyone who doubts the presence of air in unboiled water should try the experiment of adding a little of such water to two or three drops of the stock pyro solution in one glass, and a little of the boiled water to a similar quantity in another. The unboiled water, unless it is remarkably free from dissolved air, causes a brownish-red coloration to appear at the moment of mixing, whereas the boiled water does not.

Solution can be made more rapid bv crushing any of the crystals we have to dissolves the heavier solution falls awav. and mortar may he used, but they are not necessary. The substance to be crushed may be wrapped in two or three thicknesses of clean paper and then hammered or rolled; if one such treatment is not enough, the biggest unbroken lumps may be picked out and dealt with in the same way again. An earthenware jam pot makes a very useful roller for crushing crystals. The finer the powder, the greater is the area of the surface which is exposed to the solvent action of the water, arid so the more quickly does it dissolve. —An Aid to Solution.—

Another aid to solution is a little bag of muslin. Water containing some dissolved substance is heavier than water which does not contain any, and so sinks to the bottom of the vessel. If, therefore, we have anythin we wish to dissolve’ and we simply put it into a glass or bottle of water and leave it, the solid lies on the bottom, and, as it dissolves, the solution accumulates round it and prevents any more from dissolving, or at least makes the action much slower. Hence the necessity for frequent stirring or shaking. But if, instead of doing this, we enclose the substance to be dissolved in the muslin bag and hang this so that it is only just below the upper surface of the water, as the substance dissolves the heavier solution falls away.

Water which is not yet charged with the substance is constantly brought into contact with it, and solution takes place quickly and without any need for stirring. Most chemicals dissolve much more quickly in hot than in cold water; but it is not always possible to use heat. Potassium metabisulphite, for example, has some of its active constituent—sulphurdioxide or sulphurous acid—driven off if the water in which it is put is too warm, as the smell will indicate. Sodium sulphite, on the other hand, can be dissolved in very hot water without any ill effects; although, if the water is nearly boiling, the crystals will be seen to undergo a change, becoming white and opaque instead of colourless and clear. This change does not in any way affect the character of the solution.

Although most of the developing agents —pyro, nietol, amidol, hydroquinone, glycin, etc. —dissolve more rapidly in hot than in cold water, it is better not to use too hot water when dissolving them, as oxidation takes place more quickly, and oxidation is what we have to guard against. There is no reason why the water should not be warm; and my own practice when making up a developer is to let the water boil for five minutes or so, and then put the kettle on one side until it has cooled down so that the hand can bear it comfortably. If this is done, by the time all the ingredients have dissolved the solution will be at about the room temperature and ready for use. —Undissolved Particles.— A frequent source of defects in photographs is the presence of undissolved particles in the solutions. It may be that the whole of the ingredients never was completely dissolved; or the bottle containing tlie solution has been allowed to get very cold, so that some of the solids crystallised out again; or a little of the solution has dried on the lip of the bottle, whence it has been carried into the measuring glass or dish. Such undissolved particles in a developer are the cause of black spots on negatives or prints developed with it. These spots frequently have tails, making them resemble the conventional representation of a comet, the tail being due to a current in the solution carrying dissolved substances in one direction; and when they show themselves, while they may be spotted out, there is no other satisfactory icinedv.

The only way to guard against them completely would be to filter or strain each solution immediately before use; but this is neither necessary nor desirable. We can see if there are anly undissolved particles in the stock solution by looking at the bottle; and we can also see to it that the neck is wiped clean before any of the solution is poured out. —The Use of Cotton Wool.— When a solution is being made up it is very easy to make quite sure that no solid particles pass into the bottle, and the method of doing so has other advantages. Every photographer ought to have amongst his sundries a glass funnel, four or five inches across the top, and some absorbent cotton wool. The wool should be stored in a box with a lid to keep it clean.

When we are making up a solution we take a piece of cotton wool about the size of a walnut, wet it with clean water, and push it firmly into the funnel. It should be just so firm that if a little water is poured into the funnel it comes through the wool in a rapid series of drops or a very thin stream. Anything we have to dissolve we crush and put on the wool, and then pour water into the funnel. If the substance is one which does not dissolve very quickly the wool should be pushed in more tightly than otherwise, so that the water gets through more slowly.

This method should always be used when a developer is being made up for immediate use. It has been said that it encourages oxidation, and in theory it may be that it is open to this criticism. In practice, however, no ill-effects show themselves, while it is a complete guarantee against tiouble from undissolved particles.—R. C. 8., in the Amateur Photographer.