Georg Fritz

THE arrangement of the reproduction studio is essentially different to that for ordinary portrait work. The general points of such arrangements are described in detail in the handbooks of Drs. Eder and Vogel, and these I may therefore omit so far as nothing novel is to be observed.

We distinguish now between daylight and artificial light studios; further, those in which a camera is used for making the negative and those in which a dark-room itself is the camera. The first will, of course, be used where other things besides reproductions have to be made; the arrangement without a camera presents many advantages for reproduction work only. In the arrangement with artificial light the illumination of the object to be taken is effected as a rule with a source of light which can approximately replace daylight, and which also remains as constant as possible, and the electric light is at present the best. Although other sources of light are sometimes used, the electric light in the form of the arc light for continuous practical use has the advantage. For copying oil paintings daylight is to be preferred under all conditions, and for this the best arrangement is the revolving studio.1

1 See Eder’s “Jahrbuch fÜr Photographie,” 1893, p. 231.

The description of a modern studio with electric light as used in the K.u.K. Militar-geographischen Institut in Vienna, and from which the studio of the K.K. Hof-und Staatsdruckerei was copied, is given here. This studio lies seven metres below the level of the street on the south front of the building, and is shown in Fig.2.

The preparation and dark rooms are illuminated with white, yellow, and red light by means of two 50-c.p. incandescent electric lamps for each colour, and besides this are provided with window screens of glass of the same colours for daylight.

The windows open into an area 50 cm. wide which runs round the building. The lighting is so arranged here that besides the ordinary collodion plates, very sensitive gelatine plates can be worked. The room C, where the original is placed, is fitted up {31} with four Franzen arc lamps of 3,000 c.p. each for illuminating the original, and the lamps are so arranged that the light falls centrally on the original. The four lamps are fastened by ball

Fig. 2.

A is the room for the preparation of the plates, for the wet collodion plates, and the silver bath.

B the developing room.

C is the room in which the original is placed, where is found a support for the original TT?', as is shown in Figs. 3 and 4.

D is the dark-room with the focussing table EE?' (Figs. 2 and 3), and is separated from C by a wall of 15 cm. thickness. In this wall is found the photographic lens in a metal flange built into a stout iron box.

F is the washing and polishing room for the glass plates.

and socket arms to an iron frame which rests on rollers; they can be raised or lowered on the frame, and for taking small objects can be pushed closer together. The arms are fastened to the round pillars of the frame, being provided with a screw grip. The lamps can be placed as close as 0·5 m. to the original. As a rule, however, they are worked at a distance of one metre, as then the intensity of the light is about equal to diffused daylight. The axes of the carbons in the lamps are so arranged that the glowing crater formed in the positive pole is turned to the original, by which means the illumination is intensified. The positive carbons have a diameter of 20 mm., the negative carbons 8 mm. The lamps stand in pairs one above the other at LL?'. In the two upper lamps the positive carbon is at the top and the negative carbon below it, so that the light is equally distributed over the whole of the subject. With this arrangement of the lamps all reflections are avoided, and neither the grain of rough drawing paper, the relief of an engraving, nor the edges of pieces stuck on are felt. The current is produced by a dynamo in the house; it enters into the place at N, whence it is divided into two circuits of 20 ampÈres, in which are two switches, an ammeter and a rheostat, and the two lamps on either side.

The wall in which the objective O (Figs. 3 and 4) is placed, as also the brick socle aa and ee (Fig. 2), on which the support for

Fig. 3.

Fig. 4.

{34}

the original and the focussing screen rest, run on rails, and are absolutely isolated from the brickwork of the building in order to avoid any possible vibrations.

The stand for the original TT?' is provided with screw fittings, cams and wheels, which make it possible to raise the original, to lower it, to move from right to left, and vice-versÂ, vertically and horizontally, so as to place its centre axial with the optical axis of the lens, as well as parallel to the focussing screen in the dark room. The whole of the mechanism lies at the back of the stand, so that there is absolutely nothing in front of the original.

The focussing table EE?' is constructed in a similar manner to the stand for the original, and is movable in every direction in the same way. It carries in front two wood clips, in which the board with the original is placed. The table for the original, like the focussing table, is constructed on rollers, which run on the already-mentioned rails. In order to be able to fix these as soon as a sharp focus is obtained a brake is fitted. The placing of the original table at the distance from the lens is accommodated according to the size in which it is to be reproduced, and has already been estimated. There remains, therefore, only to trouble about the fine focussing, which is very quickly effected.

For taking line or wash drawings and for enlargements up to 80×80 cm. a Steinheil wide-angle aplanat is used, which gives no distortion. The duration of exposure is with such subjects from eight to ten minutes. For smaller subjects, and principally for photographs on wood, an orthoscope by VoightlÄnder is used, and the exposure varies from four to six minutes.

A Zeiss anastigmat is used for making autotypes. Duration of exposure from three to five minutes. Coloured objects, oil paintings, etc., are taken in the daylight studio. They are printed in the daytime in the open air, and in bad weather or under pressing circumstances in the night by the electric light.

The negative for photo-lithographic work, for whatever method it may be used, must before all things possess two principal qualities; when looked through it should be as clear and as clean as possible, on the other hand the ground as well covered as possible. The deposit must not be of a black colour; from a well-drawn original absolutely satisfactory negatives can be prepared without the black colour. When a drawing is reduced which contains grey lines, dots, and points, as well as full black ones, toned lines will be visible as well as the transparent; with careful treatment, the negative may be so far corrected that it may be used. If this is not effected, or is not possible, the retouching on the stone will be somewhat troublesome. The toned lines print later than the transparent; these will therefore be overprinted {35} when the former have scarcely reached the correct degree of printing. The choice is then only left either to weaken the lines which are too strong or to draw afterwards the faint or not printed lines.

If the ground is not sufficiently opaque it will print through. This can be remedied by intensifying the negative, or when this is not possible to paint over it as well as possible.

Transparent spots are formed on the negative by an impure silver bath or by dust flying about the room. These must be spotted out if increased work later on on the stone or zinc plate is not desired.

In reproducing fine copper engravings, it generally happens that the fine grey hair-like lines and the light interstices, if the plate was not properly polished, appear less transparent in the negative than the other parts of the picture. In developing the print the result is a partly broken image which can only be retouched with considerable trouble. The negative can be corrected by taking care to paint over the transparent parts. Professor Husnik recommends, when the picture is not too large, to fasten a transparent paper on the back of the negative, and to cover over the glassy places with a soft lead pencil. These parts then print simultaneously with the hair-like line and develop also equally. If, however, the negative is large, and the picture very complicated, a glass positive picture is prepared in the following manner: A polished sheet of glass is levelled and coated with the following solution:—

Gelatine	6	parts by weight.
Sugar	1	part by weight.
Ammonium bichromate	1	part by weight.
Water	80	parts by weight.

When the solution has dried the glass plate is laid on the negative and exposed till the deepest shadows have printed, and it is then developed in water. When dry this glass positive is laid on the back of the negative so that every part of each picture fits. The plates are then bound round the edges with paper strips so that they cannot shift. By this—although somewhat troublesome—operation can an unsatisfactory negative be rendered more even.

This correction can also be effected in the following manner: The back of the negative is coated with raw collodion which is faintly coloured with aniline red, eosine or fuchsine, allowed to dry, and then with an engraving needle or a narrow knife the less transparent lines may be scraped out, so that the red collodion only remains on the transparent places. Obviously also this can be done in the reverse, by painting a faint red on the transparent places with a brush.

By this last method a tolerably extensive retouching may be {36} effected on unequal negatives, which are the result of not quite equally black or also very close drawn originals, from subjects with very fine lines, such as copper-plate engravings, or from finely-executed lithographs with very great reduction. Finally it should be mentioned that with intelligent retouching any bad negative can be used for photo-lithography, and the only question now is whether it is not better to take the shortest way and prepare a suitable negative when the original really permits of its being done. In printing on chromated gelatine paper a good result can be easier attained from somewhat foggy or thin negatives than by printing with asphalt or other light sensitive substance.

The following kinds of negatives are used for the various photo-lithographic processes:—

For the transfer process with chromated gelatine paper or direct printing on stone or zinc direct, a reversed line or autotype negative.

For Orell and FÜssli’s process, a reversed ordinary half-tone negative.

For BartÖs’ process and for photogravure on stone, a direct ordinary half-tone negative.

The preparation and cleaning of the plate glass is as follows:—First of all the plates are roughened with a piece of sharp pumice stone on the extreme edges to the breadth of about 0·5 cm. in order to prevent the frilling or floating off of the collodion film. This is very little trouble considering the advantage it offers. After being edged the plates are placed in a solution of

Instead of nitric acid, chromic acid may be used, but this is not absolutely necessary.

After one or two hours the plates are taken out of the acid bath, well washed under a strong water rose, and dried in a place free from dust. Then the plates are well rubbed with 1:10 tincture of iodine solution with a pad of clean filter paper and then polished with 50 per cent. alcohol. This preparation must be done with absolute accuracy, and thus they make all substrata of albumen, india-rubber solution, etc., for direct negatives unnecessary.

Plates which have been previously used are placed in pure water till the collodion film has become loose, and are then scrubbed with a stiff brush, treated for some hours to a bath of caustic soda, and then treated as above, when they may be used again. {37}

For reproduction of simple line drawings iodized collodion is used which consists of 2 per cent. raw collodion composed of—

Iodizing is done with

The last salt is dissolved in a few drops of distilled water, the other salts are dissolved in one part of the absolute alcohol. The iodizing solution is filtered into the raw collodion, which has already been allowed to settle and filtered, and allowed to stand for some days.

The sensitizing solution is nitrate of silver in the proportion of 1:10, with larger sizes 1 to 12–1 to 14, and the silver bath is faintly acidulated with chemically pure nitric acid.

For a monochrome subject the exposure lasts according to the size of the reproduction, and the rapidity of the objective, from three to ten minutes.

For development an iron developer is used, consisting of:—

The iron developer, with addition of sulphate of copper, is to be preferred for short exposures to iron and lead developer. If the plate has been correctly exposed the image gradually appears after a short time, and very soon gets vigorous. When the details appear in the deepest shadows the development must be immediately stopped, otherwise fogging will ensue. If the image does not gain vigour by long development it was under-exposed; with over-exposure the image appears quickly and remains thin. The developer, when fresh, works fairly quickly; older developers work slower, but give very clear negatives.

For very fine line drawings or reproductions of copper-plate engravings the developer is used somewhat weaker, and one-fifth of its volume of water added. The development takes somewhat longer; the fine lines remain, however, very clear.

After developing the plate is well washed and then intensified first with a solution of—

to which a few drops of a 1:12 silver nitrate solution have been added. Care should be taken that in the first intensification the glassy places remain clear. When, therefore, the desired opacity is attained the plate should be immediately washed. Too long intensification fogs the finer lines.

The plate should be fixed with 5 per cent. solution of potassium cyanide. For this, however, a concentrated solution of hyposulphite of soda can be used.

After well washing, the negative will show, when examined by transmitted light, whether the ground is opaque enough, or whether a further intensification is necessary. With correct manipulation this first intensification will be sufficient for fine, well-prepared drawings.

If, however, the opacity proves to be too little, after thoroughly well washing, the second intensification or blackening is effected with a concentrated solution of mercuric chloride in distilled water, which is allowed to act till there is a distinct precipitate and the film has become grey. After well washing the plate is flowed over with solution of thiosulphate of gold till the grey quicksilver precipitate has become absolutely black. The gold solution consists of—

Immediately before use solution A is added with constant stirring to solution B, and a few drops of ammonia added. If the desired blackening is not effected with one application the operation must be completed.

The solution of gold, when kept in the dark, will keep a long time.

For fixed negative the following intensifiers have been used with good results:—

1. Intensifier with pyrogallol.

To this solution is added—

2. The hydrochinone intensifier recommended by Baron HÜbl:—

To this as much acid is added as will keep the solution clear for {39} five minutes, when it is mixed with a third of its quantity of 1:30 solution of silver nitrate. The addition of a few drops of sulphuric acid or 5 parts of citric acid is generally enough. This intensifier acts somewhat more delicately than the silver and iron solution, and has the advantage over the pyrogallol that it can be applied as frequently as desired in full daylight to the fixed negatives without any danger.

3. The metol intensifier.

The negative should be developed with the above-mentioned iron solution:—

The negative must be fixed before intensification with hypo and well washed.

A small quantity of solution A is poured over the negative to drive off the water, and then it is intensified in the ordinary way with 10 parts of solution A and 1 part of solution B.

Further intensification is effected, as described, with mercury, the blackening with thiosulphate of gold.

When the negative is finished and dried it is coated with a solution of gelatine 1:50, or a 1:15 solution of gum, in order to protect the film, and the negative should be levelled and allowed to dry.

Good opacity in the ground and clear glass in the lines of the drawing are the fundamental requirements of a negative for photo-lithography. But drawings are not always prepared in such a manner that this can be completely obtained. With flat drawings which are drawn in grey instead of black the first intensification is only continued till the finest lines appear clear. For further intensification the negative after drying is given a coating of a light sensitive solution of—

Ammonia is now added till a light colour is formed. After drying it is exposed from the glass side to 15° Vogel’s photometer, washed for about a quarter of an hour and then soaked in warm water till a relief is formed. By this operation a transparent relief is formed on the lines of the drawing, which absolutely protects the same from fogging. The intensification is then effected with mercuric chloride and chloride of gold, or an intensifier of {40} solutions of uranium and ferridcyanide is used, which is composed of two solutions—

The negative is first flooded with the uranium solution and then with the red prussiate.

Another process of intensification recommended by Prof. Eder and Toth is the so-called lead intensifier.

The somewhat under-exposed negative ought only to be developed with iron, fixed with hypo, and must then be well washed. It is finally well rinsed with distilled water, and then placed in a filtered solution of—

After a few minutes it becomes absolutely opaque in the covered parts. The negative is allowed to remain in the bath till it has attained the desired density. On the silver molecules of the image a pale yellow precipitate has formed by the action of the lead bath. The ferridcyanide of potash is reduced by the silver to yellow ferrocyanide of potash, and gives then, with the lead salt, an insoluble compound, ferrocyanide of lead. By the action of ammonium sulphide the unstable lead salt is converted into a stable salt.

As soon as the negative has been taken from the lead bath and well washed, till the washing water no longer gives a blue precipitate, it is flowed over with dilute ammonium sulphide 1:5. Sodium sulphydrate may also be used. The image becomes black instantaneously. The negative becomes generally vigorous; if, however, it was exposed too long the fine hair lines and points veil over very easily.

If the negative is not sufficiently intensified, which may happen with very much under-exposed negatives, it should after well washing, and before treating with ammonium sulphydrate, be laid in a bath of—

in which it becomes still whiter, and should then be treated with the ammonium sulphide. The lead, the cadmium, and the silver of the bath are converted by the ammonium sulphydrate into sulphide. The negatives treated with cadmium have a yellowish tinge, whilst those treated with lead are pure black. For {41} clearing up the white-lead image when it is too vigorous or is foggy hyposulphite of soda or a dilute solution of potassium cyanide can be used. This manipulation, however, requires great care. The negative treated with ammonium sulphide if foggy can be cleared up with hydrochloric acid, used weak and repeatedly poured on and off, with careful watching of the action. After this it must be well washed.

The lead solution will remain clear for weeks, and if it begins to work slowly can be freshened up with addition of lead nitrate and ferridcyanide of potash.

If stripping negatives are to be prepared, it is advisable, with the lead intensified negatives, to give the glass plate a preliminary rub with vaseline oil, to well wash, and then to coat with raw collodion.

Husnik’s graphite intensification is still to be mentioned, which, in some cases, may be of great service, but requires practice and care.

The expert photo-mechanical worker will adopt one or the other methods for his work, and as soon as he can work safely and without hesitation he will adhere to that.

As regards the preparation of autotype negatives from simple black originals—wash drawings—the above photographic processes are quite sufficient. For taking painted originals—such as oil paintings, water-colour drawings, fresco, and pastell drawings—an orthochromatic collodion must be used if a correct rendering of the tones in the negative is to be obtained.

In our studio we have obtained excellent results with two kinds of colour sensitive collodion. These are the isochromatic collodion emulsion prepared by Dr. E. Albert and that suggested by Major von HÜbl. In using the former, the glass plates as soon as they are taken out of the acid bath and well washed must be given a substratum of the following solution:—

to which is added—

The solution should be filtered and coated whilst warm, and the plate dried in a room free from dust at least 15° R.

For the production of the sensitiveness, or for the production of the correct reproduction of the colours, two eoside of silver dyes, R. and P., are used. The P. dye gives great sensitiveness, and is especially suitable for portraits, landscapes, etc. In using this a {42} correct reproduction of the red must be abandoned, whilst the R. dye gives an absolutely correct colour rendering but requires about double the exposure. Ten ccm. of the eoside of silver solution are added to 100 ccm. of the emulsion. When coloured the emulsion will only keep for one or two days.

The time of exposure with the R. dye is normally from one-and-a-half to three minutes.

After exposure the plate must be well washed under a tap and then allowed to thoroughly drain, or otherwise developing streaks will show.

Hydrochinone developer is used for developing, consisting of three solutions:—

This developing liquid is concentrated, and is used as follows:—

To obtain hard negatives solution B is increased from 1 to 5 times. A mixture of 150 parts of the above solution with 1000 parts of distilled water forms the actual developer. By the addition of more concentrated developer or increasing the quantity of water the developer may be suited to the character of the subject. The developer must be freely flowed over the plate, and then the plate fixed with sodium hyposulphite. Intensification is effected with—

and when dissolved

are added.

Immediately before use 100 parts of solution A are mixed with 5 parts of solution B, and the intensification continued till the desired density is obtained. Negatives can be reduced by placing them whilst damp in a solution of—

When this has acted sufficiently, the plate is well washed, {43} flowed over with a five per cent. solution of potassium cyanide, and then well washed. When the dyed emulsion is used this must be done, after developing, in red light.

A very excellent method of preparing an orthochromatic collodion emulsion has been described by HÜbl,2 which can be used either wet or dry. Repeated trials made in the Imperial Military Geographical Institute, in our establishment, and in the Photographic Institute in Vienna have proved the advantageous use of this method for orthochromatic work. The raw emulsion, according to HÜbl, is prepared as follows:—40 g. of silver nitrate are dissolved in 50 ccm. of warm distilled water, and as much ammonia added as will give a clear solution; then 100 ccm. of alcohol are added and the whole allowed to cool. 30 g. of ammonium bromide are dissolved in 35 ccm. of water and 70 ccm. of absolute alcohol with gentle heat.

To make the emulsion 450 ccm. of four per cent. raw collodion are placed in a strong glass flask which will hold a litre, and to this in the dark room the silver solution added. Some of the wool separates out, but by vigorous shaking this can again be dissolved. A part of the silver salt also remains suspended in the liquid in the form of fine crystals. The ammonium bromide is added in three or four parts whilst warm. After shaking thoroughly for several minutes the emulsion is precipitated by distilled water, which is repeatedly added till the separation is complete. The emulsion, which is now powdery, is placed on a linen filter, washed several times with distilled water, squeezed to press out the last of the water, damped two or three times with alcohol, and then pressed. Whilst still damp with alcohol the emulsion is dissolved in from 800 to 1,000 ccm. of alcohol and ether, mixed with 0·5 grs. of codeine, and allowed to rest for some days, when it will be ready for use.

The preparation of the eoside of silver solution is effected as follows:—10 g. of yellow-shade eosine are dissolved in 250 ccm. of boiling water and 5 grs. of silver nitrate in 50 ccm. of water added hot. The solution is allowed to settle, then filtered, and then washed first with boiling water and then with alcohol on the filter, and then dried in a dimly-lighted room.

To prepare the dye solution 0·5 g. of the dry eoside of silver and 1 g. of ammonium acetate are gently heated together in 30 ccm. of alcohol till dissolved, then 120 ccm. of alcohol and 10 ccm. of glacial acetic acid are added, and the whole filtered. For plates to be exposed wet, 5–10 ccm. of glycerine are added. The emulsion is sensitized by adding one-tenth of its volume of dye, and should be well shaken before coating the plates. The glass plates should receive a preliminary substratum of gelatine or india-rubber, so that the frilling of the film and impurities of the glass plates may be totally avoided. {44}

For small sized plates the emulsion is used somewhat thicker than for larger, and for the latter it should be diluted with alcohol and ether. After coating they should be dried at about 15° C., and then for some minutes exposed to a temperature of 30° C.

The plates should be developed with the following mixture:—25 g. of sodium sulphite should be dissolved in 40 ccm. of warm water, then 10 g. of glycine added and 50 g. of potassium carbonate, at first in small quantities in consequence of the evolution of carbonic acid. When cool about 75 ccm. of a thin pasty liquid will be obtained, which may be kept as a stock solution, and before use must be well shaken and diluted with from 12–15 times the quantity of water. Wet plates should be washed before development, and the developer flowed on; dry plates should not be washed, and should be developed in a dish.

They should be fixed in sodium hyposulphite. The intensification may be effected with metol (see p. 39), and the blackening as described on p. 38.

Obviously the collodion emulsion may be used for ordinary work undyed.

The qualities of the cross-lined screen and the distance of the same from the sensitive plate will be described in Chapter V.

For the different photo-lithographic work direct and reversed negatives are used; for the transfer process direct negatives are used; for printing direct on to the stone or plate, reversed negatives.

For making the latter various methods are used, the principal of which are as follows:—

Fig. 5 shows the arrangement in which the prism a is placed in front of the lens b. The prism is three-cornered and the angle turned to the objective is a right angle. The hypothenuse is silvered. It is mounted in brass or nickel; on the mount is a screw, by means of which it is fastened to the objective, so that the side opposite to the hypothenuse lies upright to the side of the camera, and this position must be an exact right angle to the focussing screen. The camera itself must be absolutely horizontal. The subject to be taken, instead of being in front of the camera, is placed sideways to the prism. The image passes through a?', falls on the silvered hypothenuse a?, from there through the objective b, through the box-shaped extension c and the camera d, on to the sensitive plate, which is not visible in the diagram. The exposure with the prism is about 1?/?5th longer than usual, because a portion of the light is absorbed by the prism.

The photographic manipulations, the preparation, sensitizing and developing of the plates, etc., is exactly the same as with direct negatives.

An india-rubber solution, consisting of equal parts of benzole and chloroform, in which an equal part by weight of india-rubber is dissolved, is used as a substratum. When the solution has become quite clear, the unreversed and unvarnished negative is coated with it. When the film is dry, a coating of raw collodion, to which some drops of castor oil have been added, is given. When this film is quite dry, it is cut through near the edges with a sharp knife, and the glass plate and film placed in a dish filled with water, when the negative film will loosen from the glass and after some time will swim in the water. In this operation the use of force must be avoided. The film is lifted from the water by placing a card {46} underneath it, carefully dried with fibre paper, then laid flat and pressed somewhat between tissue paper. The negative prepared in this way has many disadvantages. First of all, the film is easily injured, and, therefore, the edges should be bound with strips of paper in order to protect it from tearing; further, the film is easily folded and does not remain accurately of the same size, which makes it useless for certain purposes. Moreover, this process is somewhat costly. It is now almost entirely replaced by a process in which a gelatine substratum is used.

This process is as follows:—The unvarnished negative is accurately levelled with a level and coated 2 mm. thick with a solution of—

The above quantity is quite sufficient for at least four negatives 21×26 cm. Many omit the acetic acid, but I have found that it is an advantage for the slow drying, the pliability, and the keeping of its size of the negative, to use acetic acid in moderate quantities. To a certain degree the addition of glycerine also effects this, but not sufficiently enough. Before pouring on the gelatine solution, the plate must be absolutely dry. Any air bells formed whilst coating must be pushed to the edge of the plate with a piece of card. The plate must be dried spontaneously in a room as airy and as free from dust as possible. In order to protect the film from dust particles, it is advisable to give it a paper cap or cardboard cover, which allows the access of air, and obviously it ought not to touch the film.

When the gelatine film has become thoroughly hard, it should be coated with negative varnish, and, after again drying, should be cut round the edges with a sharp knife right through to the glass and stripped from the plate.

If the glass was well-cleaned and prepared, as has been previously described on page 41, any gelatine film thus prepared will well and safely strip without a substratum.

With dirty or old plates, a substratum of a 1–2% solution of india-rubber should be used.

After stripping, the gelatine films are best kept between filter-papers and under glass plates.