R. G. HARRIS

In preparing to discuss the subject of toning lantern slides made on ordinary gelatine lantern plates, I mast confess to having a rather decided bias against the operation. My opinion is that the finest slides are those in which the exact color is obtained by development, and I believe experienced workers incline to the same opinion.

When toning lantern slides there is always some danger of the gelatine becoming stained by the toning agent; in which case the high lights, which should be absolutely transparent gelatine, have their original purity degraded by the ground color of the slide. This fault is especially notice-able when toning slides with the uranium and ferricyanide toning bath. Unless very great care has been exercised a brown tint pervades the whole of the slide where clear gelatine should exist, due to the toning agent having stained the gelatine at the same time that it toned the image.

Many, if not all, toning processes have, at the same time, a slight intensifying action, and this intensification makes itself unpleasantly apparent when the slide dries, as the shadows usually become very heavy, losing the transparency one usually finds in slides that have not been subjected to toning operations.

Slides will either be toned from a black to a warm color or vice versa, and the most satisfactory results in toning are those obtained when a warm colored image is toned down towards black. If black images are toned to a very warm color the decided change is often accompanied by loss of quality, due to the length of time occupied in toning, or to the strength of solutions employed.

To tone a warm colored image to darker colors, platinum, gold sulphocyanide, and palladium may be employed; while to tone a black image redder, one has to employ either copper or uranium fer-ricyanide, unless the image is converted into some haloid and again developed. Of these various toning agents the platinum bath for dark colors aud the ferricyanide for warm colors are the most satisfactory.

A sulphocyanide toning bath, similar to that used for prints, may be employed to tone a warm colored image, but the color of the slide, if toned too far, becomes purplish black, and it is questionable whether such a color looks well in lantern slides. "Photographic purples" as they have been described, are best confined to silver prints, as the instances in which they suit the subject rarely occur in lantern slide work. The following formula may be used when a sulphocyanide toning bath is wanted.

Ammonium Sulpho-cyanide, 60 grains. Gold tri-chloride, 5 grains. Water, 16 ounces.

The gold should be dissolved in half the amount of water given, and the sulphocyanide in the remaining half, the solution of gold being added slowly to the sulphocyanide solution, stirring this all the time. Some form of platinum behaves even better. It should be noted that potassium chloro-platinite is the particular salt recommended, and not platinum bichloride. This latter salt is often quite acid with hydrochloric acid, and requires neutralizing first with some alkali and then reacidifying with nitric acid. If potassium chloro-platinite is used, no trouble will be experienced.

I have found that the formula usually given for platinum toning baths are too weak, requiring an inconveniently long time before any marked change is effected. The following bath is much more concentrated then usually recommended, but gives very good results in my hands :

Potassium Chloro platinite, 5 grains.

G-old tri-chloride, 5 grains

Hydrochloric Acid, 10 minims.

Water, 5 ounces.

Platinum toning, if carried very far, intensifies the image slightly, so that should an attempt be made to tone a red colored slide quite black the slide might be found worthless on drying from the adventitious opacity acquired in toning. The most suitable slide for toning is one devoid of any great shadow masses, and one which wants just a little additional density to make it a perfect slide. The following modification of the gold-platinum bath is very convenient, as with it the increase of density is scarcely noticeable :

Sodium Phosphate, 50 grains. Gold tri-chloride, 5 grains. Potassium Chloro-Platinite, 5 grain. Water, 5 ounces.

The bath must be used fresh, and will not keep. Toning with it is very rapid, but a pure black color is not readily procurable. Toning slides from black to warm is less easy than the foregoing, besides the alteration of color. Copper toning appears to give better results than uranium, as the staining of the gelatine previously referred to when speaking of uranium toning does not take place. Mr. Ferguson, who has done a large amount of experimental work in copper toning, recommends ten per solutions of copper sulphate, potassium ferricyanide, and neutral potassium citrate. To prepare toning bath we take:

Cupric Sulphate (10 per cent solution), 140 minims.

Potassium Ferricyanide (10 per cent solution) 120 m.

Potassium Citrate (neutral) 10 per cent" ) 4 ounces.

The potassium citrate is added to the copper sulphate, and then the potassium ferricyanide is poured in, when a clear green solution results, which keeps well 2nd tones readily, without staining, from purple black to red. Uranium is less satisfactory than copper owing to its liability to stain. As, however, beautiful results can be obtained with careful working, by the process. I do not feel justified in excluding it from notice. The exact strength does not seem of much importance, a stronger solution merely working quicker. The following is a convenient strength.

Potassium Ferricyanide, 5 grains.

Uranium Nitrate, 5 grains.

Acetic Acid (glacial) 1 1/2 drams.

Water, 2 ounces.

After toning, the slide is washed in running water for about ten minutes. Care has to be taken not to wash too long, otherwise the brown color is washed out, leaving the image in a very unsatisfactory condition. Uranium toned slides should be varnished when dry to prevent fading.

A very pleasant bluish green color may be given to a lantern slide that has been toned with the uranium toning bath if it is well washed and immersed in the following:

Hydrochloric Acid, 20 grains. • Iron Perchloride solution, 10 minims.

Water, 5 ounces.

The color obtained is very suitable for foliage subjects, but as the gelatine is stained throughout the slide any subjects with masses of high lights do not look well. The green color, however, can be discharged from any portion of the slide by treating it with a weak solution (say twenty per cent) of ammonia. Thus, the sky portion, where the stain shows more objectionably, can be cleared. Again, a slide, having been toned brown with uranium, can have certain portions of it toned green by applying with a camel hair brush the iron solution given previously; in this way a slide with two colors results, and some subjects look very effective when done in this manner.

In spite of the variety of results that can be obtained by toning methods, I would urge upon the lantern slide worker to devote all his care to gaining a high class slide by the unsophisticated process of development. Redticing and intensifying methods are of greater importance than toning formula. However expert and careful one may be, a certain proportion of his work will always be the better for re-adjustment in one direction or the other. Either some portion of the slide is over-dense and requires reduction locally, or the whole slide would be better for just a trifle more opacity. Lantern slides, unlike negatives, require their opacity to be exact, or the effect when they are projected upon the screen . is unsatisfactory.

The reducer introduced by Mr. H. Farmer is particularly useful in slide work if not used too strong. One and a half grains to the ounce is quite strong enough, though for local reductions of dense portions this may be slightly exceeded. The most convenient way of making up this reducer is to keep a ten per cent solution of the potassium ferricyanide made up, and to add ten or twenty minims of this to each ounce of water. The amount of hyposulphite left in the film and upon the surface of the plate when it is removed from the fixing bath is quite sufficient to effect reduction, though after reduction and a good rinse the plate may be replaced in the fixing bath for some minutes with advantage.

A good lantern plate with suitable developer should, on being removed from the fixing bath, show perfect freedom from any surface marks or deposit, except that which forms the image. Occasionally when developing for warm colors, an irregular white deposit occurs on the film. This may be removed by washing and rubbing slightly with a tuft of cotton wool, but the ferric-yanide reducer is much simpler and safer. A weak solution is flowed over the plate two or three times, just long enough to remove the deposit without reducing the image. A reliable in-tensifier is especially useful when making slides having warm colors, as these slides are not easy to obtain of the exact density. The following formula may be relied upon to give perfectly satisfactory results without the least influence upon the color.

A. Hydrokinooe, 20 grains. Citric Acid, 20 grains. Distilled water, 20 ounces.

B. Silver nitrate, 20 grains. Nitric Acid, 5 minims. Distilled water. 20 ounces.

Equal parts are taken to form the intensifier. The plate should be well washed after fixing and placed for some minutus in an alum bath, and again well washed before intensification. As the intensified slide, when dry, is somewhat denser than it appears when wet, allowance must be made for this and intensification stopped somewhat short of the required degree. The plate is rinsed thoroughly under the tap after intensifying and placed in the fixing bath for a short time to remove any silver chloride that may have been precipitated in the film. Another intensifier of considerable value to the lantern slide maker is that of M. M. Lumiere. The formula is:

Sodium Sulphite, 1 1/4 ounces. Mercuric Iodide, 20 grains. Water, 6 ounces.

The slide on leaving the fixing bath is well rinsed and flowed over with the above intensifier when density goon accrues. After a good washing, the slide is redeveloped with some developer such as amidol, etc.