The toning baths for bromide papers may, as a rule, be used also for lantern slides. A good platinum formula, which will not necessarily be suitable for gaslight slides, is:

Platinum Chloride....... 1 gr.

Hydrochloric Acid....... 1 min.

Water.........10 oz.


Nothing is more trying to spectators than a series of landscapes in which the sky is represented by clear glass, without clouds or indication of atmosphere - that is, nothing except bad clouds. The sky must receive from the lanternist even more care than it demands in the ordinary print. The lighting of the sky must come from the right quarter, and a sunlit landscape must not be rendered ridiculous by heavy storm-clouds which throw no shadow whatever on the background. Sometimes, especially in winter pictures, sophistication is profitable; that is, a suggestion of clouds in the contact-printed slide by means of judiciously applied green paint on the glass side of the negative. The reflections of such clouds should not be forgotten, if there are stretches of water in the scene.

The best way of introducing clouds is to print them by contact on a second plate, which will perform the function of a cover glass; one incidental advantage is that, if the clouds, either by over-printing or lack of tone, prove incongruous, they can be transferred to another slide. Light printing is nearly always the best for such clouds.

Transfer Slides

We have already given some directions for slides by the carbon process under that section. An ordinary P.O.P. print may, without very great difficulty, be mounted as a lantern slide. Bleach and clear an old lantern plate until the gelatine is as clean as the glass. Harden with formaline and allow to dry. Then take any P.O.P. print, freshly toned and fixed, if possible, and one that has not been treated with either alum or formaline. Squeegee it while wet into contact with the lantern plate (film side, of course), and paint the back with glycerine. After a little warmth applied at the fire the paper will peel off, and leave the toned print ready for mounting as a lantern slide.

The ordinary collodion, or gelatine P.O.P., emulsions have occasionally been coated on lantern plates, but somehow or other have not proved commercially successful. Exquisite effects may, however, be obtained by treating ordinary gaslight plates for one minute in a 1 per cent. solution of sodium salicylate. These plates will print out by daylight, when dry, and will tone in any gold bath.

Masking And Mounting

All slides should be masked; and some thought should be given to the shape and size of mask to be used for each particular picture. The rectangular shape is much better than all others; except for portraiture, we should use it in all cases. Binding on the cover glasses will not be found very difficult after a little practice, and various devices have been invented to assist the inexpert. Before binding, two white spots must be placed on the front top corners of the slide for the guidance of the lanternist, though sometimes these spots are provided for on the binding strips.

Before binding up, the cover glasses ought to be scrupulously clean, and the film of the plate clear from dust, holes, or scratches, which would all be immensely exaggerated when projected upon the screen. A coat of crystal celluloid varnish will help to preserve the life of the slide and render it less liable to injury from an over-heated lantern. Lantern slides, by the way, should always be unpacked and exposed to warmth and air for about half an hour before the commencement of a lecture. We know of one architectural authority who prefers his slides shown cold, on the ground that the slight condensation of moisture on the film improves the gradation in sculpture and suchlike subjects. But we have registered a solemn resolution not to lend him any of our cherished plates.