which in some cases is comparatively easy, in others very difficult.
If we are working by reduction from a good-sized negative, with a fairly even horizon, the difficulty is not great. The landscape part of the negative is first exposed, the sky being masked if necessary, and a cloud negative is then subst.i.tuted for the landscape negative, a part of the former being masked to correspond with the landscape on the latter, and a second exposure is made on the same slide-plate. Admittedly in all cases this requires "some doing," in many cases it is extremely difficult. An easier, if less "sportsmanlike," method is to make the cloud slide on a separate slide-plate, and to use the latter as a "cover-gla.s.s" for the slide.
The cloud may cover the whole of the second slide, and that part of it not required may be wiped out by means of a reducing solution, used with a brush, such as the ferricyanide and hypo one described later. This method will be found useful even in contact slide making, but it also requires not only good taste in the selection of the cloud, but some deftness in manipulation; but the neat-handed beginner need not fear to make the attempt.
DEVELOPMENT.
It has already been stated that judgment of exposure is a matter of experience, and that results are the best criterion; here follow some more explicit statements on the same matter.
Whatever plate or developer is used, and whatever the time occupied in complete development:
_1st._--If by the time the high-lights are sufficiently strong the shadows are too dense or blocked, the plate has been under-exposed.
_2nd._--If by the time the high-lights are sufficiently strong the shadows have not attained sufficient density, or are veiled, the plate has been over-exposed.
_3rd._--If at the same moment the high-lights show sufficiently and the shadows are transparent but sufficiently plucky, the plate has been properly exposed.
_4th._--With a normal negative the normal exposure is the proper exposure; but (_a_) a negative abnormally strong in contrasts will require an abnormally long exposure; and (_b_) a thin negative, or one with a very short scale of gradation from densest to clearest, will require an abnormally short exposure, with probably some after-treatment in the direction of "intensification."
Ambitious slide-makers generally aim at warm-toned slides for pictorial effect, and rightly. But slides intended for scientific purposes are generally better when cold in tone, the definition is usually better. But whatever the aim, a good tone of one kind is preferable to a poor one of another kind, and the beginner should first make sure of getting a really good cold tone, which is comparatively easy, and then try his ""prentice hand" on warm tones.
Warm tones are obtained by using greatly super-normal exposures and greatly restrained developers; and the danger probably lies in the fact that the long exposures are apt to lead to fog, and the great restraint to over-density in the shadows, the latter especially when the exposure has not been quite long enough for the developer used; herein probably lies the whole secret of warm slide-making. If we aim at really warm tones and use developers suited to such design, we must on no account stint the exposure.
COLD TONE DEVELOPING SOLUTIONS.
[Ill.u.s.tration]
The cla.s.sical solution for cold tone slides is a solution of ferrous oxalate in pota.s.sic oxalate. Of all developers it is most free from fogging propensities. It is made from so-called "saturated solutions" of proto-sulphate of iron and pota.s.sium oxalate. Thus, into a bottle put a quant.i.ty of iron proto-sulphate, and pour on about three times its weight of water containing a dram of sulphuric acid to each pint. Shake well, and keep always at about 60 Fahr.; some of the iron must always be visible in the bottle, if not, more is to be added. The crystals of iron salt must be green and not rusty in colour. This is the "iron solution."
The "oxalate solution" is made by dissolving pota.s.sium oxalate in about three times its weight of water. This also must be kept at 60 Fahr., shaken occasionally, and oxalate added if none is visible in the bottle.
To make the ferrous oxalate solution we _pour_ one part of the iron solution _into_ six parts of the oxalate, and it is advisable to add to each ounce of developer at least half a grain of pota.s.sium bromide; 5 minims of a 10% solution, made by dissolving one ounce of the bromide in about 9 ounces of water, and then making up to 10 ounces--all chemical.
In about four minutes or less this ought to fully develop a properly exposed plate. If the development is much shorter the slide is apt to have an unpleasant greenish tone, a result that may also follow the use of an inordinate amount of bromide in the developer. The developing solution may be made in quant.i.ty greater than is required for one plate, and may be used several times if a little of the surplus and fresh solution is added when the quant.i.ty in use becomes slow in action.
For really fine cold black tones the following formula by MESSRS.
ELLIOTT & SON will be found admirable:--
A Metol 40 grains.
Soda sulphite 1 ounce.
Water 8 ounces.
B Pota.s.sium carbonate 120 grains.
Ammonium bromide 24 "
Pota.s.sium bromide 48 "
Water 8 ounces.
The developing solution consists of equal parts of A and B.
If either of the above developers is to be used, the exposure is to be kept down as compared with the exposure to be followed by developers intended for very warm tones.
The two developers which follow next, require about the same exposure as the two already formulated. "Ortol" is a reducing agent quite lately introduced by Mr. Hauff, of Feuerbach in Germany, and Mr. Hauff"s agents in this country are Messrs. Fuerst Bros., of London. "Ortol" gives the finest tones of the warm black type that we have as yet come across, it is singularly free from fogging propensity, and the tones do not easily degenerate into the greens so apt to occur after severe over-exposure with other "black"
developers. We suggest a simple formula:--
A Water 20 ounces.
Metabisulphite of pota.s.sium 75 grains.
Ortol 150 grains.
B Water 20 ounces.
Soda carbonate 3-1/2 ounces.
Soda sulphite 2-1/2 ounces.
To make the developer, take one part of A, one of B, and one of water, and to each ounce of the mixture add one and a half or two grains of pota.s.sium bromide. The development of a properly exposed slide will take two or three minutes, and the result will probably be highly appreciated.
The above is worthy to stand alone as representing developers for warm black tones, but the following works well. (Messrs. Elliott & Son.)
A Hydroquinone 80 grains.
Soda sulphite 1 ounce.
Pota.s.sium bromide 15 grains.
Water 10 ounces.
B Caustic soda 80 grains.
Water 10 ozs.
The developing solution consists of equal parts of A and B, and the plate may be fully developed in about two to three minutes.
It has already been stated that in order to obtain really warm red or reddish tones by development, it is necessary to give very long exposure, and to use a developer very much restrained. It is further found that carbonate of ammonia has a considerable effect in reddening the developed image, and so we now come to procedure based on these lines. Carbonate of ammonia is found in commerce in the shape of "chunks" more or less square. If one of these is pared with a knife--unless the sample is quite fresh--the outside will be found to be a soft amorphous powder, the inside a clear, very hard crystal; the clear crystal is in development an "accelerator," though a very weak one, the outside substance is a restrainer. Probably both the inside--sesquicarbonate--and the outside--bicarbonate--are useful, and the best plan is to make a ten per cent. solution of the substance as obtained from a good chemist--not druggist. Of this solution one grain of the salt is represented by ten minims. If now we take an ounce of A, and one of B of the last formula, and if we add to the ounce of A 3 grains of ammonium bromide, and to the ounce of B 3 grains of ammonium carbonate, and if we have given a proper exposure and develop with equal parts of the A and B modified as above, we shall get a slide of rich chocolate colour; and if we double the proportions of carbonate and bromide, and expose still longer, we shall get a slide still ruddier in tone, even to red. But there is always danger of fog, and of clogged shadows, and this must be reckoned with. There is a more certain and less dangerous way of getting handsome tones, which shall be described presently.
Gelatine slides are always fixed in hyposulphite of soda, about one part by weight to six parts of water; after this they must be well washed, say five minutes under a good rose tap, or in many changes of water in a dish for an hour, and every slide should be treated with a saturated solution of potash alum, of which each pint should contain a dram of hydrochloric acid.
Very many, if not most, slides are all the better for just a touch of a "reducer" such as follows:--The ordinary "hypo." solution is weakened with about four times its measure of water, and the plate is soaked for a minute in this. A few drops of a ten per cent.
solution of pota.s.sium ferricyanide are put into the measure, and the hypo. mixed with it, and the whole allowed to work on the plate for a short time, carefully watched. Of course a weak slide must not be thus treated, but it is often a good plan to develop slides to such a point that they will permit of this treatment.
On the other hand it is often advisable to keep a slide thin in development, for instance, when the negative wants pluck, and intensification is indicated; or when we wish a good warm tone after a "black" developer such as our metol formula: a good average treatment is as follows:--
Take half an ounce each of ammonium chloride and mercury bichloride and dissolve in 16 ounces of water, soak the slide in this till it is bleached. Wash well and treat with weak liquid ammonia, or a solution of soda sulphite, or of metabisulphite of potash, or fresh lime water. This will strengthen the slide and give it in most cases a fine rich colour. It is important to let these solutions act thoroughly, and not to stop the action half-way. The writer considers this the best and safest way to obtain warm tones, the reader may find out for himself which of these solutions produces the tones he chiefly affects.
Crystal varnish is _not_ wasted even on a gelatine slide.
In conclusion, it must be realized that the screen-image is a greatly enlarged edition of the slide-image; any small defect on the slide is a huge one on the screen. Consequently the slide-maker must sedulously cultivate cleanliness and manipulative care.
_Andrew Pringle._
[Ill.u.s.tration: Fishing Smacks. W. Thomas. ]
_How to make Enlargements._