A negative whose size bears a proportion similar to 3 1/4 by 3 1/4 will lend itself more easily to reduction; thus whole-plate or half-plate negatives are easy of manipulation in this respect, and require but little doing up. But as other sizes have at times to be copied into a disc 3 1/4 by 3 1/4, recourse must be had to a sort of squaring of the negative.
In a good lantern transparency, it is, of all things, indispenable that the high lights be represented by pure glass, absolutely clean in the sense of its being free from any fog or deposit, to even the slightest degree; it is also necessary that it be free from everything of heaviness or smudginess in the details. To obtain these results, you may have recourse to the strengthening of the high lights of the negatives, and this is done with a camel-hair brush and india ink, working on the glass side.
The apparatus may be a whole-plate camera, very strongly made, and with a draw of 23 in. when fully extended. Use a Ross rapid symmetrical lens on 5 in. focus, a broken-down printing frame with the springs taken off, and a sheet of ground glass. This is all that is required, though it is generally believed that a special camera is required for this work, such as to exclude all light between the negative and the lens. There is nothing to hinder the use of ordinary cameras, provided the draw is long enough, and the lens a short focus one.
Take the negative and place it in the printing frame, holding it in its place with a couple of tacks, film side next the lens, just as in printing; then stand the printing frame on its edge on the flat board, and place the ground glass in front of it, between the light and the negative. The ground glass can conveniently be placed in another printing frame, and both placed up against each other. Then bring the camera into play, and so adjust the draw and distance from the negative till you get the picture within the disc on the ground glass. The best way is to gum a transparency mask on the inside of the ground glass; this permits of the picture being more easily brought within the required register. This done, focus sharply, cap the lens, and then proceed to make the exposure.
Regarding exposure. Bear in mind again that it is merely a printing process we are following up, as you will all know that in printing no 2 negatives are alike in the time they require. So in this case, no 2 negatives are the same in their required exposure. Still, with the plates used, so wide is their range for exposure, that but few failures will be made on this score, provided we are on the safe side, and expose fully.
Although these plates are not nearly so fast as gelatine plates, they give good results in about 1 1/2 minute by burning magnesium ribbon. Never allow the ribbon, when burning, to remain in one position, but keep it moving from side to side, and up and down, in front of the ground glass while making the exposure; and if there be any dense place in the negative which, as in printing, would have required printing specially up, allow the light to act more strongly on that part; the result, as a rule, will be an evenly and well exposed plate.
To coil up the ribbon before setting it alight, take an ordinary lead pencil and wind the ribbon round and round, thus making a sort of spiral spring; this done, gently pull the coils asunder, then grasp the end of the ribbon with a pair of pincers, light the other end, and make the exposure.
For development, use a canary light, with which you can easily see to read a newspaper. The canary medium is inserted between 2 sheets of glass 7 1/4 in. by 4 1/2 in., the 2 glasses are then fastened on to the tin with gummed paper, a few holes are bored in the back for air, a funnel is let in, and the thing is complete.
The formula for development is as follows: -
Pyro........ 96 gr.
Methylated spirits .. 1 oz.
Potash bromide .. .. 12 gr.
Water........ 1 oz.
Ammonia carbonate .. 60 gr.
Water........ 1 oz.
Mix 30 drops pyro with 30-60 drops bromide, then add 2 dr. ammonia solution and 2 dr. water.
A thin negative requires a slow development, and so. gains contrast; while hard negatives are best over-exposed and quickly developed.
The plate is first placed in water or rinsed under a gentle stream from the tap till all greasiness has disappeared, it is then placed in a flat dish, and the developer is applied. Should it be found that some parts of the picture are denser printed than they should be, by the ribbon acting more strongly on some particular part - this is often the case if the negative has been thinner in some parts than others through uneven coating of the plate - the picture need not be discarded as a failure.
Fix the plate in hypo - the fixing takes place very quickly - then examine the picture for the faults above described; if they are found, wash the plate under the tap gently, and bring into operation a camel-hair brush and a weak solution of potassium cyanide. Apply the brush to the over-printed parts, taking care not to work on the places that are not too dense. Do not be afraid to use plenty of washing while this is being done; let it be, as it were, a touch of the brush and then a dash of water, and you will soon reduce the over-printed parts. It only requires a little care in applying the brush.
After this wash well, and should it be deemed necessary to give a black tone, use a weak solution of platinum bichloride and gold chloride, or a very weak solution of iridium, in equal quantities, allowing the picture to lie in the solution till the colour has changed right through to the back of the glass. Should a warm pinkish tone be desired, tone with weak solutions of potassium ferricyanide, uranium nitrate, and gold chloride in about equal quantities.