Our plate is now ready for development, and for this purpose we make up the following good all-round developer :—
Sulphite of soda .... 2 ounces. Bromide of potassium . . .30 grains. Water to make up . . . .20 ounces.
To make up this No. 1 proceed as follows :—Dissolve 2 ounces of sulphite of soda in 10 or 12 ounces of water and then add bromide of potassium and the hydroquinone and make up to 20 oz. with water.
Sodium hydrate . . . .160 grains. Water to make up . . . .20 ounces.
It is always advisable to shake up both bottles before using them.
Hydroquinone will almost refuse to act in cases where it is used at a very low temperature, and many failures to obtain satisfactory slides can be traced to using developers at too cold a temperature ; for use take \ ounce No. 1 and \ ounce No. 2 and 1 ounce of water and mix well.
Place the lantern plate in the dish and flow over it the developer in one even sweep, taking care that no air-bubbles appear. Keep the developer moving, and if exposure has been correct the image should appear in thirty seconds to one minute, and development will be completed in about three or four minutes. It should develop up clear and strong, without hard, harsh contrast, and with soft gradations from high lights to shadows. If slower in coming up it indicates under-exposure, and the result will be dense shadows and clear glass high lights. If it comes up too quickly the result will be flat, and lacking in contrast or gradation.
The making of technically good slides is purely one of practice, just as in negative-making. When to stop development is always the point where the beginner fails, and it is a point in which but little help can be given him.
It is, however, advisable, when the image comes up nicely and gradually, with all its parts in order, to just overdevelop it. That is to say, when the picture has reached its best to the eye let it go a little further and appear to be 15 per cent, overdone. This will be reduced away in the fixing, and the result should be correct.
Take the plate out of the developer and wash well under a flow of clean water and fix, as in negative-making, for ten or fifteen minutes.
The fixing bath, which must always be used quite clean, is made as follows :—
Hyposulphite of soda ... 5 ounces Water......20 ,,
When the slide comes from this fixing bath it must be well washed just as a negative, and dried away from all possible chance of dust.
The slide is best examined when dry, as we can then better judge the points. The colour should be a warm black, which is very pleasing for a great variety of subjects. The colour, to a great extent, is regulated by the quality of the negative, the exposure given to it, and the developer used. A good average negative exposed fully and developed with a normal developer will yield a nice warm colour, yet the same negative exposed just enough will result in a colder colour. Thus it will be seen it is possible to obtain a long range of colours upon the same make of plate and developer by varying the exposure.
Good negatives give the most satisfactory results in slide-making, as in all other photographic processes.
A very poor, thin negative does not give the same scope, and whilst a good slide can be made from a poor negative by skilful treatment, it is only a makeshift.
A hard, harsh negative should be given a liberal exposure or be even over-exposed to aid in building up gradations that are not easily printed from such a negative.
The worker is strongly advised to keep to one developer. It will be really surprising what can be got out of it when one comes to know it well, and to do this it must be in constant use.
Two other formulae of well-tried developers are here given :—
Sulphite of soda ... 2 ounces Water to make up . . 20
Potassium carbonate . . 300 grains.
Ammonium bromide . . 60
Potassium bromide . . 120
Water to make up . .20 ounces.
For use, take equal parts of each.
Length of time taken in developing, two to three minutes.
Sulphite of soda . . . 1 Water to make . . 20
Ammonia bromide . . . 150 grains Ammonia -8oo . . . 200 minims Water to make ... 20 ounces.
Time to develop, about five minutes. This gives a good image on the screen.
Now the process of development in the making of lantern slides can only be learned by experience, but it is surprising how easy it is with a little practice to learn to make slides of good uniform quality.
There is one important point to observe in developing slides, and that is as regards the density. We will explain. If the slides are to be shown in a small room and upon a small sheet by lime-light, the dense slides will appear best; yet if the same slide is shown in a large public hall upon a sheet double the size and with the same lantern, the slide will appear hopelessly black. It is best to make slides of fair average density to suit public-hall work, and if they at any time have to be used in a smaller room and they appear too thin, less light can be used upon them through the lantern. Thus it often happens when slides are judged at exhibition upon small sheets the dense ones look better and so gain the awards, yet the slides look hopelessly at fault when they are shown in public. These slides should be judged upon a full-size sheet to do them justice.
A good lantern slide may be said to be one in which the whole of the image is of the most translucent character, in which the colour of the deposit caused by the developer is pleasing, and in which the tone values and gradations are proportioned in such a manner as to be suitable to the character of the light that comes from the lantern.