Julius Schnauss

Negatives Suitable for Collotype.

A COLLOTYPE plate may be readily produced from any negative, but the highest results are naturally only obtained when the negative is prepared with a view to its special use. First should be considered the question—May the negative, without detriment to the finished print, be utilised without a reversal? In the not very frequent case of this important point being immaterial, it is simply necessary to produce the negative on patent plate, and it is at once available for printing from. As the negative may easily sustain damage in any of the various operations, it should be thinly and evenly varnished; this, while affording protection, does not mar the sharpness of the resulting print to any appreciable extent.

Reversed Negatives.—In the majority of cases, the resulting copy has to exactly correspond with the original as regards the position left and right, and in such cases the negatives will have to be reversed. This is usually effected in one of four different ways—

1. Reversal of the image by reflection with a prism or mirror, or reversing the plate. 2. Stripping the negative from the glass.

3. By the dusting on or powder process.

4. By the use of negative films.

The second is that usually adopted. With regard to the special features desirable in negatives for Collotype, one giving a good silver print will answer equally well for Collotype—they should incline rather to softness than the other extreme. It has been remarked that they should be as free from veil or fog as possible, and may be intensified or not according to the judgment of the operator.

Portraits from Nature, with their fine half-tone, and at the same time necessary contrast of light and shade, are the most difficult to reproduce in Collotype. The negatives should be perfect in gradation, and such as are usually only obtainable from a talented operator who has the lighting of his studio entirely under his control.

Black and White subjects, on the contrary, for their satisfactory reproduction, require a negative of the utmost density, but perfectly clear in the lines. Such are better produced by the collodion process, as directed for photo-lithography. For subjects in lines or dots entirely free from half-tone, photo-lithography is more suitable for reproduction than Collotype, where price is a consideration.

Reversal by Reflection, by means of a mirror or prism, necessitates a special and rather expensive apparatus, and the exposure being somewhat lengthened, it is, although quite successful, more suitable for lifeless objects. Stripping the Collodion Film is a safe and cheap procedure for producing the necessary reversal, and in the subsequent printing operations the danger of breakage, when compared with glass, is reduced to a minimum. The glass plate, free from defects, must be well cleaned, and it is safer, and renders the stripping more certain, if it be covered with a fine film of pure beeswax. This is best applied by rubbing over the surface a few drops of a solution of beeswax in benzole and carefully polishing, at the same time avoiding the entire removal of the wax. The piece of linen used in the operation should be rubbed upon a lump of wax previous to the polishing. The plate must on no account be gelatinised or albumenised, except round the edge only, as a precaution against premature slipping.[J] Use a tough collodion, and otherwise proceed as usual for the wet process. After the negative is finally washed and dried it should be varnished with a thin solution of gum arabic, to which has been added a few drops of a solution of chrome alum. After complete drying the margin or edges of the plate are rubbed with a little tallow. To prevent overflow the plate is accurately levelled and flooded with a solution of 10 parts gelatine soaked in 60 parts of water and dissolved by heat, to which is added 20 parts of alcohol and 6 parts of glycerine, using 1 dram of the solution to each four square inches. A few drops of phenyl, carbolic or salicylic acid may be added to the solution as a preservative, and the whole before use well filtered, while hot, through linen. The hotter the solution during the pouring on the more evenly the coating will run upon the glass, and it may be assisted in its flow by careful tilting of the plate. The use of paper strips is dangerous, and, notwithstanding the gum, extremely liable to damage the negative.

Reversal of the Plate, either collodion or gelatine, is another method of securing reversed negatives, and consists simply in inserting the sensitised plate in the dark slide with the uncoated side towards the interior of the camera. A modification of the dark slide may be necessary, and it will be obvious that the ground glass focussing screen must be reversed, or the focus corrected after the insertion of the dark slide by shortening the camera a distance equal to the thickness of the sensitive plate. Dry plates present great advantages in this method, but, in development, density must be judged entirely by transmitted light, as the image is formed in, not upon, the film. As the rays of light pass through the glass to the sensitive surface, it is necessary that the uncoated surface be quite clean, and the glass itself should be perfectly free from bubbles, scratches, or other marks.

The plate should remain in its levelled position for about fifteen minutes to set and then be carefully removed to a safe and airy position, gelatine side outwards, and allowed to dry. This operation will probably take two days; the hot gelatine layer should be about 3 mm. thick. The negative may then be coated with a toughened collodion (one or two per cent. of castor oil added to plain collodion). The plate is placed aside, and in an hour will probably be dry and ready for the next and final operation. Cut with a knife through the film, take it by one corner, and, without pause or hesitation, strip it from the glass.

Any necessary retouching should be done upon the gelatine surface after roughing it sufficiently with pumice powder to enable it to take the pencil, and all such work must be completed before removing the film, particularly if it has been damaged, as in such places the colour used in retouching would cause an adherence, and the film would almost assuredly tear in stripping.

Upon the quantity of gelatine solution used the nature of the film depends. It should be entirely free from air bubbles. Too thick a layer almost always cockles, and does not lie flat during printing, in consequence of which portions of the picture will not be sharp in the print. On the other hand, too thin a layer is extremely awkward to handle in the larger sizes, and it is preferable to transfer it in a reversed position to a sheet of plate glass coated with indiarubber solution.

Gelatine Plates for Stripping are in the market. In their preparation it is necessary to first coat the glass with a solution of yellow wax in benzole, or an indiarubber solution, before coating with emulsion, such plates being known as strippers in America and Germany. When finished, the negative is placed, together with a gelatine film—or “skin”—in a solution of glycerine and water, both are withdrawn together, a squeegee applied to remove the superfluous solution, and the negative, with its adhering skin, placed aside to dry. Afterwards the edges of the film are cut through, and the negative removed from the glass.

Stripping the Film off Gelatine Negatives for Collotype.

In the Photographisches Archiv, Mr. Wilh. Otto, a well-known German Collotype printer, describes the following process:—

“The glass plates are first cleaned by being well rubbed with a solution of caustic potash, after which they are thoroughly rinsed and polished with tripoli. The next proceeding is to wax them by rubbing one face over with a solution of 12 grains of beeswax to one ounce of ether, this being applied by means of a piece of cotton or linen cloth saturated with the solution. In polishing off the excess of waxing solution, care must be taken not to destroy the continuity of the extremely thin and almost invisible film of wax which it is necessary to leave on the glass to ensure the easy and complete separation of the film. Some operators prefer to wax the plates by warming them to a temperature somewhat over the melting point of wax, then rubbing one face over with a lump of the article, the excess being now polished off with a piece of flannel before the temperature of the glass falls below the melting point of the wax. It may be mentioned that, before waxing, it is as well to mark the working surface of each plate by making a diamond scratch in one corner.

“A small piece of cloth, moistened with ether or benzole, is now used to remove all traces of wax from the edges of the plates, a margin of the width of an inch being sufficient; and it is well to paint this margin with albumen and to allow it to dry. Unless the edges of the plate are entirely free from all traces of wax, there will be a great probability of the film separating from the glasses at too early a stage, and adhesion at the edges is made more certain by the use of albumen. A moderately diluted solution of silicate of soda may be used instead of albumen.

“The waxed side of each glass is now coated with collodion containing a little castor oil; eight grains of tough pyroxyline and three drops of castor oil to each ounce of mixed solvents (equal volume of alcohol and ether) being a convenient preparation.

“The collodion being dry, the plates are coated with emulsion. The emulsion flows very badly on the collodionised surface, but by using a bow made of a piece of sewing cotton stretched across an arc of thin iron wire the difficulty may be readily overcome. The thread is to be drawn over the surface of the plate after the required quantity of emulsion has been poured on, and it is scarcely necessary to say that the glass should be supported on a levelling stand.

“Plates prepared in this way are developed and fixed in the ordinary manner, and when a plate is dry it is sufficient to cut through the film inside the edge which has been cleaned of wax, when the film negative can be easily stripped off. In this case, however, the film is very thin, and it is often desirable to thicken it somewhat before stripping. For this purpose a piece of thin commercial sheet gelatine is taken, and soaked in water till it becomes quite flaccid, and this is laid on the negative, care being taken that no air is enclosed between them. A sheet of wet paper, or of mackintosh, is now laid on the gelatine film, and all excess of water expelled from between the negative and the soft gelatine film by stroking the upper surface of the paper, or of the mackintosh cloth, with a squeegee—that is to say, with a strip of indiarubber set in a wooden handle.

“It is now easy to remove the paper or the indiarubber cloth which was used to protect the soft gelatine from the action of the squeegee, and the plate can be set up to dry. When dry, the film is cut through within the border from which the wax was cleared off, and the film will separate readily; but should there be any tendency towards a too early separation, owing to the contractile force of the fresh thickness of gelatine, the edges of the plate may be bound with strips of gummed paper.” (Photographic News.)

Stripping Ordinary Gelatine Plates.—Any make of dry plate may be stripped by the following method:—The plate is coated with strong tough collodion upon the gelatine side; as soon as the collodion has set, it is plunged into cold water and washed until all greasiness disappears. In the meantime, a piece of “flexible support,” as used in carbon printing, is carefully waxed by rubbing upon its surface a solution of turpentine 140 cc., beeswax 2 gm., resin 6.5 gm. This should be applied evenly by means of a piece of flannel, the solvent allowed to evaporate, and the waxed surface polished with a second piece of flannel. The support should then be placed in cold water and allowed to become quite flexible, in which state it may be used at any time. Remove the negative from the clean water, and place in a bath of methylated spirits 150 cc., glycerine 3 cc., water 30 cc., hydrofluoric acid 3 cc. An ebonite, guttapercha, or lead dish should be used to contain this solution, with which the fingers should come in contact as little as possible. The film should be watched narrowly, and when loose upon the glass—but not actually detached—the plate, still bearing the film, should be placed in a bath of clean water, well washed, and all surface moisture absorbed by careful blotting. Take the flexible support from the water in which it has been standing, and without removing any adherent moisture, carefully lower it upon the film, which is still resting upon its original glass plate, squeegee it into contact with the negative film, avoiding air bubbles, place under a weight, and allow to stand for ten minutes or a quarter of an hour. The film will then be found to adhere to the flexible support, and may be readily removed from the glass. It should be allowed to dry spontaneously upon the support, no attempt being made to remove the film until it is “bone” dry, when it will readily part with the temporary support, remain perfectly flat, and may be printed from either side with perfectly satisfactory results. Should any of the waxing solution remain on the surface of the film, it may be removed by the careful application of a little turpentine applied on a small linen pad. Do not use methylated spirit for this purpose, as it may cause the film to “buckle.” Any stripped films may be conveniently preserved and kept flat between the leaves of a book.

The Powder Process is one of importance for reproducing and, at the same time and at one operation, reversing negatives, but for some reason is far more resorted to upon the Continent than in England, where few only have been able to thoroughly master it. Failures are usually attributed to changeability in the climate, but, although success is by no means uniform, it is a thoroughly workable process. The basis is a chromated solution of gum arabic, with which a plate is coated, dried, and in a thoroughly dry condition exposed to the light under a negative. The greater the extent to which the light acts, the smaller will be the amount of moisture the coating of the plate will absorb when exposed to a damp atmosphere. If the surface of the plate be now dusted over with a fine powder, as drop black, or graphite, the greater the amount of moisture certain parts of the film have absorbed, the greater will be the amount of colour such parts will retain, and so exactly reproduce the light and shade of the original negative. Simple as this process reads, the difficulties must not be underrated, and the operator will probably find plenty of opportunity for the exercise of his patience and ingenuity. A consideration of the process as just described will show that a plate which has only been subjected to a short exposure will, on dusting over and development, be found to exhibit greater density than one that has received a longer exposure, a careful adjustment of which will give to the operator great control over the density and characteristics of the reproduced negative, a power certainly too important to be overlooked. A reliable formula for the preparation of a gum-chromate solution for this process is due to Dr. Leisegang:—

which, after careful filtration, is poured over a well cleaned and dusted glass plate. After draining a little by standing on blotting paper, dry over a spirit lamp, and place, while still warm, under a negative in the printing frame—one minute in the sun, 10 to 20 minutes in the shade, is about the necessary exposure. As previously mentioned, the shorter the exposure, the denser will be the resulting negative, a result at variance to any other photographic printing operation. To develop the picture the glass plate is placed, coated side upwards, upon a sheet of clean white paper, then, with a soft camel-hair brush, dust over the picture some very finely-ground Siberian graphite, working the same backwards and forwards over the plate until the necessary strength is attained. If the picture should develop too quickly, and take the colour all over, the cause is under exposure; should the powder adhere unevenly, or the picture present a smudgy appearance, the coating must have absorbed too much moisture, and must be again warmed before further development. This precaution is particularly necessary during the winter months. If a prolonged development be necessary, and after continuous dusting a picture lacking in contrast be the result, it is occasioned by over exposure. On completion of the development the picture should be finally and carefully dusted with a soft brush to remove the superfluous powder, coated with a thin plain collodion, and placed in water, which should be frequently changed, until it fails to show any trace of yellowness. The plate should be afterwards retouched and varnished.

Negative Films have now been before the public some time, and have been considerably used as reversed negatives by printing with the back of the film in contact with the plate. The four principal varieties are, in the order of their introduction—1st, Eastman’s; 2nd, Froedman’s; 3rd, Pumphrey’s.

Eastman’s Stripping Film consists of a substantial paper coated with a layer of soluble gelatine, upon which is spread a coating of insoluble gelatine emulsion; they may be exposed in contact with a sheet of glass in an ordinary dark slide in the film carriers or on the roller slide. There are no special precautions necessary in the development, except that no alum may be used previous to stripping. For use as reversed negatives the ordinary operations are greatly shortened and simplified. A sheet of plate glass is coated with collodion, allowed to set, and then placed in a dish of cold water until all greasiness has disappeared. After fixing and washing, the negative, still supported upon the paper, is placed over the collodionised plate in the same dish, and the two brought out face to face. Upon the back of the negative paper place a piece of blotting paper, cover it with a sheet of oiled paper—as used in copying letters—and apply the squeegee; place a dry sheet of blotting paper upon the back of the film, cover it with a sheet of glass or other flat surface, upon which place a weight. In fifteen minutes the plate may be placed in warm water—about 130° F.—and in a short time the paper backing will float off. By gentle washing with hot water remove the soluble gelatine from the film resting upon the glass, and place the negative aside to dry. It is then complete, and reversed.

Froedman’s Films consist entirely of gelatine, require no stripping, and may be printed from either side. The film is somewhat difficult to handle in the developer, and has to be dried by spirit. One feature against their employment in Collotype is a yellow stain, which probably arises from the bichromate with which the film is hardened, and although more apparent where the negative is protected by the rebate of the dark slide, it undoubtedly pervades the whole picture.

Pumphrey’s Lifting Films are the latest and best of a series of films introduced by the same maker. They consist of a basis of paper coated with a waterproof varnish on one side, upon the other being spread an indiarubber coating possessing considerable adhesive power; to this is attached the gelatine film proper, which consists of two layers, one of plain gelatine, and the other the sensitive emulsion. The films should be exposed in the camera between two glass plates, and the spring of the dark slide should be of considerable strength to insure flatness of the film, and consequent sharpness of the image. The films during development may be treated exactly as an ordinary plate, the manufacturer recommending Beach’s developer. When in the bath they seem little liable to damage, and may be handled with great freedom and facility. Upon completion of the development, fixing, and washing, the paper backing or support is attached by means of paste to a substantial and smooth card. As a precaution, not always necessary, but usually advisable, against the film prematurely separating from its support, around the edges gummed paper strips may be attached to the card, and allowed to extend over the edges of the gelatine film to the extent of 3 mm. When dry the film may be varnished, and afterwards lifted from its support by first cutting through the gelatine and passing the blade of the knife round the edges between the film and the temporary paper backing, the latter remaining attached to the card. The two are by these means readily separated, and the resulting negative film may be printed from either side without disadvantage, and is of sufficient strength to withstand a considerable amount of rough handling.

Other Methods of Reversal.—There are processes of copying, usually by first producing a transparency and from that again a negative. If the wet process is used throughout, a copying camera is essential in both stages. Should dry plates, however, be used, the transparency may be produced in the camera and the negative by contact in a printing frame, or vice versa, or both may be produced by means of the camera. If the transparency be produced by the carbon process a negative may then be made from it by contact, and the necessary reversal will be brought about without the use of the copying camera.