Photography, Old Time/Photographic Printing.

Photographic Printing.

Sensitive papers ought not to be exposed in the frame until they are quite dry. The shutter at the back of the frame is removed, and the negative laid flat upon the glass, collodion-side uppermost. A sheet of sensitive paper is then placed upon the negative, sensitive-side downwards, next comes a layer of thick felt; and the whole is then tightly compressed by replacing and bolting down the shutter. The amount of pressure required is not very considerable, but if the springs of the frame become too weak after a time, a few pieces of mill-board may be placed beneath them.

The time of exposure to light varies much with the density of the negative and the power of the actinic rays, as influenced by the season of the year and weather. If the exposure to light has been correct the print appears slightly darker than it is intended to remain. The toning bath dissolves away the lighter shades, and reduces the intensity, for which allowance is made in the exposure to light. A little experience soon teaches the proper point but much will depend upon the state of the toning bath, and albuminized paper will require to be printed somewhat more deeply than plain paper. If, on removal from the printing-frame, a peculiar spotted appearance is seen, produced by unequal darkening of the chloride of silver, either the nitrate bath is too weak, the sheet removed from its surface too speedily, or the paper is of inferior quality.

If, in the exposure to ordinary diffused daylight, the shadows of the proof became very decidedly coppery before the lights are sufficiently printed, the negative is in fault. Ammonio-nitrate paper highly salted is particularly liable to this excess of reduction, and especially so if the light is powerful.

Toning.

The print should be first washed in common water until the soluble nitrate of silver is removed. This is known to be the case when the liquid flows away clear; the first milkiness being caused by the soluble carbonates and chlorides in the water precipitating the nitrate of silver. Ten minutes in water running slowly from a tap will be sufficient to cleanse a print from nitrate of silver; or three or four changes in a dish, pouring off quite dry between each change. It is an advantage to finish off with a solution of salt (2 grs. to the oz.) Pour the toning bath out into a flat dish, and put the prints into it 2 or 3 at a time, waving the dish meanwhile backwards and forwards to secure a constant movement. Continue to keep the prints moving, and watch the changes in color.

If the prints are removed as soon as the blue color of the gold is seen, they will usually change in the fixing bath to a warm shade of brown, but when left for 2 or 3 minutes longer in the toning bath, the darker tint becomes permanent.

Fixing.

One oz. of hyposulphite of soda dissolved in 3 oz. of water would fix two batches of stereoscopic prints, 20 in each batch. Allow the prints to remain in the fixing bath for 20 minutes, with occasional movement after which they may be transferred to a dish of clean water.

Washing.

It is essential to wash out every trace of hyposulphite of soda from the print, if it is to be preserved from fading, and to do this properly requires care.

Always wash with running water when it can be obtained, and choose a large shallow vessel exposing a considerable surface in preference to one of lesser diameter.

A constant dribbling of water must be maintained for 4 or 5 hours, and the prints should not lie together too closely, or the water will not find its way between them. When the prints have been thoroughly washed, blot them off between sheets of porous paper and hang them up to dry.

Mounting.

Mount the proofs with a solution of gelatine in hot water, freshly made; gum-water, prepared from the finest commercial gum, and free from acidity, may also be used, but it should be made very thick, so as not to sink into the paper, or produce "cockling up" of the cardboard on drying.

Positive Printing by Development.

Negative printing processes will be found useful during the dull winter months, and at other times when the light is feeble, or where it is required to produce a large number of impressions from a negative in a short space of time. The proofs, however, as thus obtained, are not equal to direct sun-prints in beauty and gradation of tone.

Take of iodide of potassium, 120 grs.; bromide of ammonium, 30 grs.; water, 20 oz.

Float the paper on the iodizing bath until it ceases to curl up, and lies flat upon the liquid: then pin up to dry in the usual way.

Render sensitive upon a bath of aceto-nitrate of silver, containing 30 grs. of nitrate of silver with 30 minims of glacial acetic acid to each oz. of water.

Place the dried sheets in contact with the negative in a pressure frame, and expose to a feeble light. About 30 seconds will be an average time upon a dull winter's day, when it would be impossible to paint in the ordinary way. Develop by immersion in a saturated solution of gallic acid. After the picture is fully brought out, wash in cold and subsequently in warm water, to remove the gallic acid, which, if allowed to remain, would discolor the hyposulphite bath. Fix the print in a solution of hyposulphite of soda, one part to two of water, continuing the action until the yellow color of the iodide disappears. Wash thoroughly in plenty of water.

Negative Printing Process upon Chloride of Silver.

To salt the papers, prepare the following solution: Chloride of ammonium, 100 grs.; citric acid, 56 grs.; sesquicarbonate of soda, 66 grs; gelatine, 40 grs.; distilled water, 20 oz. Float the sheets for 1 minute; render sensitive upon a bath of aceto-nitrate of silver. Take of nitrate of silver 30 grs.; glacial acetic acid, 30 minims; water, 1 oz. Float the papers upon this bath for 3 minutes, and suspend them to dry. The exposure to light is conducted in the ordinary printing frame.

The developing solution is prepared as follows: Gallic acid, 2 grs.; water, 1 oz. Filter through blotting-paper, to remove floating particles, which would produce spots in this process; pour the solution of gallic acid into a glat dish, and immerse the prints, 2 or 3 at a time, moving them about, and using a glass rod to remove air-bubbles; wash the prints for several minutes in 1 or 2 changes of water, in order to extract the gallic acid; tone in bath of chloride of gold and phosphate of soda; fix in hyposulphite, and wash.

Russell's Tannin Process, Modified.

Cleaning the Plate.

In order to clean the plates, make a stock solution of 2 oz. of bichromate of potash, 2 oz. of sulphuric acid, and 1 qt. of water (a green quart wine bottle may be used). Pour the solution into a shallow tray; soak in it the plates to be cleansed, and ofterwards wash the plates in water and dry them; then pour on each plate a small quantity of old collodion; rub it all over the plate with a tuft of cotton, and then clean it off with a dry linen cloth. It will perfect the cleaning if the plate be dipped in pure water and again dried with a clean linen cloth. The bichromate of potash solution may be filtered back into the bottle for future use.

To Coat the Plate.

1. Cover the plate with a bromised collodion. Take care, in all cases, gently to oscillate on running off the excess of collodion, or white marks, visible in a subsequent stage of the process, will be formed.
2. When the film is somewhat fixed, put the plate, by the aid of a dipper, in a well-bath of a 50 gr. nitrate of silver solution, and let it remain in the solution 10 minutes.
3. Put the plate in a well-bath of distilled water until what are called the "greasy" marks disappear.
4. Put the plate in a well-bath of a 10 gr. solution of bromide of ammonium, or cadmium, or magnesium, or of potassium. It may be best to adopt that bromide which enters into the preperation of the collodion. Let the plate remain in this solution about 1 minute. Occasionally filter this bath solution, in order to remove the excess of bromide of silver which is deposited in the bath. Keep a stock bottle of this bromide solution to supply the waste drippings.
5. Put the plate for a short time in a well-bath of distilled water.
6. Wipe the back of the plate, and let it drain for a short time, and then place it in a well-bath of 10 or 15 grs. of tannin to the oz. of distilled water; let the plate remain in this solution 4 or 5 minutes, and then, on removing it from this bath, let it rest on one end, to dry. When dry, it is ready for the camera, and it will keep a long time. It should be rapidly and evenly dried, and a stone bottle of hot water may be so used as to hasten the drying. Tannin which dissolves most easily in water, is to be preferred. Add to the tannin bath 3 or 4 drops of creosote, and it will keep clear. A little experience will show how long a time the plate must be exposed to light in the camera. It will be best, in the beginning, not to make a very short exposure; harsh pictures are the result of long exposures, and soft pictures of short exposures to the light. These plates will bear a considerable amount of exposure in the camera without being fogged - even for 10 minutes.

Developing.

1. The film sometimes appears to be in a rotten state, and to crack up when water is poured on it. This will not happen if a small quantity of alcohol be added to the water solution first poured over it.
2. Take a solution of 2 grs. to the oz. of water of carbonate of ammonia; add to it some alcohol, and flush the plate with it; pour this off into a glass, and add to it from 1/2 gr. to 1 gr. of pyro-gallic acid, in solution, and pour it back again on the plate. This picture will instantly appear, and the details may be allowed to come out well. The image will not be dark.
3. Pour off the alkaline pyro-solution, and gently wash the plate; add a few drops of citric acid (1 or two grs. of citric acid to the oz. of distilled water); pour it over the plate, and run off; or pour an acid pyro-solution over the plate instead of acid solution alone. Again gently pour distilled water on the plate, and run it off.
4. It will be found to be convenient to dissolve 1 dr. of pyrogallic acid in 1 oz. of alcohol, and to add to this 1 oz. of distilled water. Use 1 dr. graduate, and 16 minims of this solution will give 1 gr. of pyrogallic acid; also have a 2 oz. bottle of distilled water and dissolve in it 2 drs. of citric acid; 8 minims of this will be 1 gr. of citric acid. Have also an oz. bottle of a 10 gr. solution of nitrate of silver: and lastly have at band a pint bottle of distilled water, 1 or 2 glass oz. graduates, and 3 or 4 developingglasses, which hold about a fluidounce.
5. The development of a plate is completed by solutions of 1/2 gr. to 1 gr. of pyrogallic acid, and 1 gr. or more of citric acid to the oz. of water, and the addition of 1 drop to 3, 4, or more of the 10 gr. nitrate of silver solution. If the picture is strongly out when the ammonia is washed off, let it be dosed with an excess of acid silver; if feeble, let an excess of pyrogallic acid be used. If there be a sign of fogging when pushing the development with an excess of nitrate of silver, immediately pour off the developer, gently wash the plate and flush it with the 8 gr. bromide solution. The image, as it at first shows its strength or weakness, very soon teaches the manner in which the plate is to be dealt with.
6. Lastly. Gently wash the plate, fix the image with a strong solution of hyposulphite of soda, and, when the picture is "cleared," wash it with distilled or common water, and dry it.

The three steps which have made the tannin process of Major Russell simple, clean, and certain, are: First, the use of the bromide bath; second, the use of the tannin bath; and third, the use of the acid solution, either alone or mixed with pyrogallic acid, after the alkaline solution of carbonate of ammonia has been washed off, not forgetting the mixture of some alcohol with the first application of water to the film on the development.

Fothergill's Dry Process.

The directions for coating and dipping in the bath are the same as for "Russell's Process." After removing the stereoscopic plate from the nitrate bath, stand it vertically on blotting paper and allow it to drain as long as it would be required for a wet plate, wiping the back meanwhile in the usual manner.

Then take it in the left hand, either by one corner or with the pneumatic holder, and having arranged the yellow light so that it falls nicely upon the surface of the film; hold it quite level and pour on 1/2 oz. of water, waving it backwards and forwards. It should not be poured on entirely at one spot, or too much of the nitrate of silver would be displaced, producing a circular mark of imperfect development. As, however, a vacant space of a quarter of an inch in breadth is usually allowed at each end of a stereoscopic plate; this will be found convenient for pouring on the water which must be allowed to run into each corner until greasiness has disappeared. It will probably touch the fingers by which the plate is held, and when they are not scrupulously clean, stains will, in consequence, result. After pouring away the water (which ought then to measure at least 3 drs. if the operation was well performed), drain the plate for an instant, and it will be ready for the albumen.

The Albumen Solution.

Take the white of a fresh egg and add to it 1 oz. of distilled water with 3 drops of strong ammonia. Shake for 10 minutes in a bottle, and pour out the liquid on a filter previously wetted.

Apply the filtered albumen twice or thrice to the film in the same manner as collodion. Then pour water over the plate for a minute, in order to remove the excess of albumen, and afterwards rear the glass on end to drain upon blotting paper. When the plates are perfectly dry they are ready for exposure.

Development.

This process is not quick as regards development. When pyrogallic acid is used, each drachm of the liquid is previously mixed with about 5 minims of a solution of nitrate of silver, containing 20 grains to the oz. of water. The film is wetted and the mixed developer poured on and off from a glass measure.

Fix with hyposulphite of soda.

Taupenot's Collodio-Albumen Process.

Cleaning the Glasses.

This part of the process must be conducted with care. Sensitizing andWashing.

Employ 2 nitrate baths in this process, one for the collodion and the other for the second film, viz. the albumen. The albumen nitrate bath must contain free acetic acid, and therefore if one solution be employed for both films it should be a bath of aceto-nitrate.

Sensitize the collodion in the ordinary way, holding it rather longer than usual before dipping.

Having arranged 2 dishes of common water, side by side, lay the plate face uppermost in the first dish, and wave the water backwards and forwards for about 30 seconds. Then put the plate into the second dish and leave it whilst another glass is being coated and immersed in the sensitizing bath. Now drain plate No. 1 closely on blotting-paper, and it will be ready for the iodized albumen. Plate No. 2 remains in the sensitizing bath until the first glass has been coated with albumen and placed to dry.

Preparation of the Iodized Albumen.

Take of albumen, 3 oz.; distilled water, 1 oz.; strong ammonia, 10 minims; iodide of potassium, 10 grs.; bromide of ammonium, 10 grs.

First mix the ammonia and the water, then add the other ingredients and shake together in a bottle. Iodide of ammonium may be advantageously used.

To Apply the Albumen.

For a stereoscopic size, measure out 1 dr. of the albumen and pour it on and off twice to displace the surface water of the washed collodion film. Then apply a second quantity.

Stand the albuminized plates vertically on blotting paper to drain and dry.

The Aceto-nitrate Bath.

Take an ordinary collodion negative bath and add to each fluidounce 30 minims of glacial arctic acid, keep it in glass or gutta percha and continue to use it until it has become blackened by the action of the albumen. The film of albumen must be rendered quite dry by holding it to the fire before it is dipped in the aceto-nitrate bath. Leave them in the bath any time between 30 seconds and 2 minutes, and then remove the wash with water. Use two dishes for washing and allow 20 or 30 seconds in each dish; then rear up again to dry, and the plates will be ready for exposure. Artificial heat may be used with advantage.

The most successful operators in Taupenot's process give a very long exposure.

Development.

Prepare a saturated solution of gallic acid in distilled water, adding 4 grs. to each oz. Filter this developer through paper.

The solution of nitrate of silver for use with the gallic acid may be made of the strength of 20 grs. to the ounce. Add 15 minims to 1 oz. of gallic acid solution. Previous to the application of the developer the surface of the film must be moistened with water.

From half an hour to an hour must be allowed for the full development with gallic acid. Fix with a saturated solution of hyposulphite.

Pictures On Porcelain.

The plates for these pictures are sold as porcelain, but are really an opaque white glass. The plate is coated with collodion, rendered sensitive in the usual way, and the image received from a negative adjusted as follows: The negative is placed at one end of a box, the other end of which joins the front end of a camera having a quarter tube. The object of this box is to cut off extraneous light. The negative is placed toward the sun, or a piece of white paper placed in the sun. The image formed by the negative is focussed on the ground glass of the camera, in the usual manner. The box in front should admit of being varied in length, in order to alter the size of the picture, by changing the distance of the negative from the lens.

The white sensitive plate is then exposed and developed with the ordinary iron developer. After washing off with the developer, fix with a weak solution of cyanide of potassium.

The picture requires to be darkened with a weak solution of bichloride of mercury chloride of gold, or chloride of platinum. As soon as the picture appears of the proper shade arrest the action of the strenghthening agent, by washing the plate under a copious stream of water. The Wothlytype Process.

1. To Prepare the Uranic Salt.

Dissolve the ordinary commercial nitrate of uranium in distilled water; add ammonia till no more precipitate is formed. This precipitate is uranate of ammonia, insoluble in water. Wash in several waters, and then redissolve in nitric acid. The solution, crystallized and dried over a water-bath, constitutes the "uranammonium nitrium" of the specification, and is probably a double salt of uranium and ammonia. If it be very acid, dissolve in distilled water and again crystallize.

II. The Sensitizing Liquor.

To a saturated solution of the above salt in 6 oz. of distilled water add 220 grs. of nitrate of silver, previously dissolved in 1 oz. of distilled water and intimately mix. This mixture, when crystallized over a water-bath, is the salt used to sensitize the collodion. It may be kept in a bottle, but not necessarily in a dark place, because it is only sensitive to light when brought into contact with organic substances.

Dissolve 3 oz. of this salt in 10 oz. of alcohol, to which 5 drs. of distilled water and a few drops of nitric acid have been added. This is the sensitizing liquor, and does not require to be kept in the dark.

III. Preperation of the Resinized Collodion.

The collodion may be the ordinary plain preparation, containing about 5 1/2 grs. pyroxyline (not powdery) to the ounce of ether and alcohol, mixed in the proportion of 6 to 2; but, in order to give it an organic reaction with the sensitizing salt, it is necessary to add to each pint of the collodion about 10 drops of so-called "harz oel," which is thus prepared: Take equal parts of castor oil and Canada balsam; dissolve the latter in sufficient ether to enable it, when mixed with the castor oil, to pass through a filter. After filtration, evaporate the mixture over a water-bath till it is of the ordinary consistence of a fatty oil. The collodion is now ready for being sensitized.

IV. To Sensitize the Resinized Collodion.

To every 3 oz. of the collodion thus prepared add from 1 to 1 1/2 oz. of the sensitizing solution with a few drops of nitric acid, and intimately mix. The collodion is now sensitive to light, and must be kept in the dark.

V. Sizing of the Paper.

This is an important preliminary to prevent the image from sinking into the body of the paper. It is effected either by a tolerably strong solution of starch, Iceland or Irish moss, beaten up with about one-eighth its bulk of albumen and a few grains of acetate of lead. The paper may be floated on this in the usual way, and when dry is ready for the reception of the sensitive collodion.

VI. Applying the Collodion.

The paper is pinned down by 3 of its corners to a flat board, a little larger than the sheet to be collodionized. The collodion is poured on in the usual way, and the excess run off at the unpinned corner into the stockbottle. This may be done with great deliberation, and more may be poured on to any part, where there is a de-ficiency, without much chance of its running in ridges, as would inevitably be the case if a glass plate were so treated. Hang up to dry in a dark room, and it is fit for the printing-frame.

VII. Preliminary Fixing.

When the picture is printed to the proper strength, that is to say, to the depth which it is wished finally to retain - for uranic developed pictures lose very slightly in the toning and fixing process - place it in a bath containing distilled water 40 oz., acetic acid 1 oz., and hydrochloric acid 1 oz., for the space of 10 minutes. The object of this bath is to remove the uranic salts insoluble in water. The prints are afterwards washed in several waters before being placed in the toning solution.

VIII. Toning the Pictures.

The ordinary alkaline gold-bath answers very satisfactorily, and tones uranic prints much more rapidly than similar prints on chlorized paper.

IX. Fixing the Proofs.

If the picture be toned in hyposulphite of soda and gold no further fixing will be necessary; but if in the usual alkaline gold-bath, they will have to pass through a hyposulphite or sulphocyanide solution, to remove the silver salts insoluble in water. When thoroughly washed the process is complete.

Photography Without A Nitrate Of Silver Bath. (Sayce's process.)

Preparation of Collodion.

Take of bromide of cadmium, 6 grs.; bromide of ammonium, 2 grs.; soluble cotton, 6 grs.; ether and alcohol, each, 1/2 oz. Mix, and after standing a week, filter. Then take 12 grs. crust. nitrate of silver, in fine powder; add to it a drop or two of water, so as to produce a kind of pulp.

Then in a chemically dark room, mix the collodion and silver, stirring as the mixture is poured into the bottle intended for its reception. Then shake up well, and allow it to stand.

To use the Collodion in the Wet State.

Take perfectly clean plate-glass, free from scratches; tip the edges for 1/8 of an inch with a solution of 1 gr. of India-rubber in 1 oz. of benzine. Then coat with the collodiobromide of silver, allow it to set the usual time, and place it in a dish of water until the greasy appearance has vanished. Warm water is preferable when it can be procured. When the water flows freely over the film, take the plate out of the dish, wipe the back, and drain for a moment upon a piece of blotting-paper. Then place in the dark slide for exposure in the camera. Expose a little longer than wet collodion, with the nitrate-bath. Wet the film with a little water, and pour over it protosulphate of iron, 25 grs.; glacial acetic acid, 25 minims; water, 1 oz. To 3 drs. of which, 2 drops of a 20 gr. solution of nitrate of silver. Fix with cyanide of potassium 20 grs. to the oz. Intensification may be accomplished by any of the means adapted to wet plates.

To use the Collodio-Bromide in the Preperation of Tannin Plates.

Coat the plates as directed in the last paragraph and place them in a tank of water. Take the plates out of the tank in rotation, and place them in water as hot as the hand can hear, for about 30 seconds, and then into a bath of tannin solution of 15 grs. to the ounce of water well filtered. The following tannin solution is preferable: Tannin, 10 grs.; gallic acid, 5 grs.; water, 1 oz.; grape sugar, 5 grs.; alcohol, 10 minims. Dissolve the tannin in a portion of the water and filter; dissolve the gallic acid in another portion by the aid of heat, and filter; mix the two, add the grape sugar, and when dissolved, filter; then add the alcohol. If the plate be allowed to remain in the above solution three minutes, and is properly exposed, very little intensification will be necessary. Dry the plates evenly and quickly, and expose about half the usual time.

Development of the Dry Plates.

Prepare the following solutions:

1. Carbonate of ammonia, 40 grs. to water, 20 oz.
2. Pyrogallic acid, 96 grs. to alcohol, 1 oz.
3. Bromide of potassium, 10 grs. to water, 1 oz.
4. Nitrate of silver, 30 grs.; citric acid, 15 grs.; distilled water, 1 oz.

Pour over the dry plate once or twice, enough of No. 1 to cover it, and return to the bottle for use in the next plate. Then place the plate in a dish of water until the greasy appearance has vanished. Then pour evenly, enough of No. 2 with a few drops of No. 3 and two drops of No. 4 added, and wave to and fro with a rocking motion. The image should very soon appear, and may be developed until the shadows become slightly tinged. Then wash the surface and back of the plate freely with water, and rinse with a little very dilute acetic acid; say 2 drops of glacial acid to the ounce. Wash again, and if any intensification is required, it may be accomplished by adding to 2 drs. of water 3 drops of No. 3 and 3 of No. 5 solution. When dense enough, wash and fix with cyanide, 20 grs. to the ounce of water.

Failures And Imperfections.

On Glass.

1. Universal clouding from over exposure or diffused light in preparation or development of the plate, or alkalinity of the bath, or too much nitric acid in bath, or organic matter in the bath, or the use of colorless collodion; also vapors of ammonia or sulphuretted hydrogen. Such negatives may sometimes be recovered by the application of a weak solution of iodine, followed by hyposulphite of soda.
2. Spots upon the plate from excess of bromide of potassium in the collodion, impure nitrate of silver in the bath, super-saturation of the bath with iodide of silver, dust upon the glass or coating, the concentration of nitrate of silver by drying before exposure.
3. Curtain-like marks upon the edge, from the plate being too dry before dipping, not long enough in the bath to remove the greasy appearance.
4. Wavy lines, from the use of a glutinous, thick collodion from want of rocking when pouring off the collodion (common with cadmium sensitigus).
5. Rottenness of film, from bad cotton or dipping too soon after proving before properly set.
6. Oily lines, from the removal from the bath too soon.
7. Curved lines, from the developer not covering the whole plate immediately.
8. Silver stains, from reversing the plate between the bath and slide.
9. Yellow patches, imperfect removal of the iodide of silver in the fixing bath.

10. Scum upon the surface upon removal from the bath, over iodized collodion.

11. Image black and white without half tones, from underexposure in the camera.

12. Collodion curls from the glass upon drying from dirty glass, insufficient alcohol in the collodion, want of roughness of the edges of the glass.

13. Blueness of film, want of iodizer in collodion.

14. Crystals on film when dried, hyposulphite not washed entirely out.

15. Developer flows greasily, from want of alcohol in developer.

16. Circular transparent spots of large size, from pouring on the developer at one place.

On Paper.

1. Marbling and spots, from weak nitrate-bath.
2. Marbling after toning, from the prints overlying each other.
3. Spots by transmitted light, from imperfect removal of the silver salt.
4. Cold and faded appearance, from weakness of bath or excess of chloride in paper.
5. Yellowness, from acidity of bath.
6. Bronzing of deep shadows, negative is too transparent. Recovery Of Silver And Gold From Waste Solutions.

Bathe of Nitrate.

Throw down the silver as a chloride by muriatic acid; settle, pour off the clear part, and wash the precipitate; place the chloride in a dish, together with some bars of zinc, and pour over it sulphuric acid largely diluted with water (1 of acid to 60 of water). As soon as it ceases to give off gas add more acid until the zinc is entirely dissolved. Should any chloride remain add more zinc and acid. The gray powder is metallic silver, and may be run into an ingot in a crucible by mixing with twice its weight of carbonate of soda or borax.

Hyposulphite Baths.

Boil for several hours with a suspended bar of zinc, filter out the precipitate, and fuse with carbonate of soda or borax. The button contains silver and gold if the solution has been used to tone and fix prints.

Toning Baths (Alkaline).

Add a solution of sulphate of iron, filter out and wash the precipitate; digest with diluted nitric acid for several hours; filter out the residue, which is metallic gold.

All waste solutions, containing silver, in the laboratory should be run into a large vessel, and acidulated with muriatic acid every evening, and the clear liquid siphoned off in the morning; the precipitates will be principally chloride of silver, and when enough has accumulated it should be removed from the vessel, and reduced, as advised for baths of nitrate of silver.

Paper Clippings.

The clippings of sensitized paper should be preserved, and when a quantity has accumulated burned to ashes, the ashes to be in a crucible mixed with twice their weight of a mixture of carbonate of soda and borax. If carefully brought to a full red heat, and allowed to cool, the silver will be found collected into an ingot at the bottom of the crucible. It is best to trim the prints before washing or toning, but the whole of the cuttings are worth saving.

Removal of Silver Stains.

1. By rubbing with a moistened lump of cyanide of potassium, and washing freely with water. This mode is dangerous, on account of the highly poisonous nature of the cyanide.
2. By rubbing the spot with moistened iodide of potassium, then with diluted nitric acid, and then with hyposulphite of soda, and washing with water.
3. Apply a paste of chloride of lime for a few minutes, wash thoroughly with water; rub with moistened iodide of potassium, and dissolve out the iodide of silver formed by hyposulphite of soda.
4. For Linen or other Fabrics. - Rub with solution: Cyanide of potassium, 100 grs.; iodine, 10 grs.; water, 1 oz.; (very poisonous;) and wash with large amount of water.

21.1 Photolithography.

Toovely's (Patent) Photolithographic Process. From a negative on glass or paper a positive impression is taken on paper prepared in the following manner: Take sized paper, very smooth and even in texture, which coat with a solution of gum Arabic in pure water, saturated with bichromate of potash; it is known that bichromate of potash, in combination with an organic substance, such as gum, gelatine and starch, becomes insoluble in water after a certain exposure to light. The paper, prepared as above, is then exposed to light behind a negative, and when the photographic image is sufficiently developed, such parts of the gum impregnated with bichromate of potash as receive the rays of light become insoluble, or partly so, exactly according to the gradation of tone in the negative employed. The sheet of prepared paper, with the photographic image thus printed, is placed face downwards on a lithographic stone, grained very fine, or polished according to the nature of the image to be reproduced, and previously arranged in a percussion-press (it can be done in a lithographic press, but the result is uncertain). Place several sheets of damped paper upon the stone over the photographic proof, and apply a heavy pressure; the water contained in the damp paper is pressed through the photographic proof and dissolves the parts of gum remaining at liberty; the dissolved gum attaches itself to the surface of the stone. When the stone has remained a certain length of time in the press sufficient to allow the small quantity of soluble gum in the dark shadows to attach itself to the surface of the stone remove the pressure, and withdraw the photographic proof carefully from the stone; a negative image is then visible in gum on the stone, with all the gradations of tone. Dry the stone, either spontaneously or by gently warming it; when well dried, cover the whole surface of the stone with greasy ink, which may be applied with a roller or otherwise; the greasy ink is thus brought into contact with all the parts of the stone untouched by gum; the coating of ink is then removed by passing through the lithographic press, by spirits of turpentine or otherwise, and all the gum removed from the surface by washing. The stone is then rolled in with ordinary printingink, and the positive image appears in black; it is then printed as every lithographic drawing, but has the great peculiarity of requiring no etching, the gum having so far penetrated by pressure into the substance of the stone as to allow of a great number of impressions being taken off. Gum Arabic is preferable, but similar substances can be used instead such as gelatine, dextrine, and mucilaginous solutions. In photozincography proceed as above described, substituting a zinc plate for a lithographic stone.

In photographic engraving on copper, steel or other metal plates, the preliminary operations are the same as those employed for stone or zinc, excepting that a positive image on glass or paper should, in the first instance, be used instead of a negative. When the plate is withdrawn from the press, and the photographic proof detached from it it should be well dried for the stone. The plate is then covered with a thin coating of varnish, and when dry may be soaked in water to remove the gum, or immediately plunged in a weak solution of acid, and etched in the usual way of etching on steel or copper. Wherever the plate is protected from the varnish by the gum it will be attacked by the acid, and an engraving is produced, which is then printed as an ordinary etching on metal plate.

Osborne's (Patent) Photolithographic Process.

Let us suppose that a map has been compiled and drawn with great care, and that it is desired to multiply copies of this original in the lithographic process. The first step in the process is to obtain a negative; for which purpose the map is placed upright upon a plane-board, and the camera opposite to it at such a distance as to give the desired ratio between original and copy. A nega21.1. tive is now taken on glass coated with collodion in the usual way, observing the greatest care to avoid distortion of all kinds and to produce a negative of the highest excellence, success in which depends entirely upon the knowledge, judgment and experience of the operator. A sheet of plain, positive photographic paper is now coated on one side with a mixture, consisting of gelatine, softened and dissolved in water, to which a quantity of bichromate of potash and albumen has been added.

The paper, evenly covered with this fluid, is dried in the dark, when it will be found possessed of a smooth glassy surface, and a bright yellow color. This surface is still further improved by passing it through the press in contact with a polished plate.

Asuitable piece of positive photolithographic paper thus manufactured is now to be exposed to the action of the light under the negative of the map already described. This is accomplished in an ordinary pressure-frame, the time required varying from 10 to 15 seconds, or several minutes, according to the brightness of the weather. The positive thus obtained presents itself to the eye as a brown drawing upon the clear yellow of the sheet.

The exposed photographic copy of the original is covered all over, while dry, with transfer-ink, which is accomplished by running it through the press with its face in contact with a stone which has already received a coating of such ink. After it is separated from the blackened stone it will be found to have brought away with it an evenly distributed film of inky matter, forced by the pressure into intimate contact with the unexposed, as well as the exposed portion of the surface. This operation is known as "blacking" the positive print, that now to be described is called "coagulation," its object being to effect a change of that nature upon the albumen contained in the coating of the organic matter. For this purpose moisture and heat are necessary, and both are applied very simply, by letting the blackened photographic copy swim upon the surface of boiling water with its inky side upwards, for it is important not to wet that with hot water. After the lapse of a certain period, determined by the experience of the operator, he proceeds to the next step in the process, that of "washing off." For this purpose the print is laid upon a smooth surface, such as a plate of glass or porcelain, and friction with a wet sponge, or other suitable material, is applied to the black inky coating, under which the photographic image still exists, and to develop which is now the object in view. The operator soon becomes aware that the moisture which percolated through the paper from the back has exerted a softened or gelatinizing influence upon the gelatine in the sensitive coating; it has caused it to swell, and to let go its hold upon the ink. But this change does not extend to those parts of the coating which were acted on by light; in other words, to those places which were unprotected by the opacity of the negative, they remain intact, uninfluenced by the solvent or moistening effect of the water. Accordingly the operator finds a facsimile of the original map gradually develop under his hand as he continues the friction. This process is proceeded with until all traces of ink are removed, save those required to form the picture, which must be clear and distinct in all its details. Abundance of hot water is then poured over it, so as to remove every particle of soluble matter, and it is then finally dried, which completes its preparation A stone to which a fine smooth surface has been imparted, is now slightly warmed, and put in the lithographic press; upon this is placed (inverted) the positive print, after it has been damped by lying between moist paper, and the whole is then passed repeatedly through the press. On examination the paper will now be found to have attached itself firmly to the stone, so that some force is required to separate the two. When the former is removed it brings with it its albuminous coating, which gives to it while damp a parchment-like appearance; but the ink is gone: it has left the paper for the stone, and on the latter we find a reversed drawing of the map, one which, after it has been properly "prepared," will print as well as if it had been drawn by hand.

Pretsch's Process Of Photo-Galvanography.

Take a plate of glass, and spread on it ordinary glue, to which bichromate of potash and a small quantity of nitrate of silver has been added. For instance, take 2 or 3 solutions of glue, into one of which put a little nitrate of silver, into another bichromate of potash, and into another iodide of potassium. The silver and the iodide are for the purpose of producing a little iodide of silver on the sensitive film, so as to produce on the picture that grain which is necessary for holding the ink in the process of printing. Take the photographic picture obtained by any of the customary processes, and place it on the sensitive plate thus prepared and exposed to the action of the light. In the course of a short time (all those parts which are dark in the photograph, protecting the plate from change, and all those which are white, allowing the sunlight freely to pass through and the change to take place), we have a combination of bichromate of potash and gelatine in two different states, one soluble and the other insoluble. Consequently, when the plate is then put into water all the parts which remain soluble are dissolved out, whilst the other parts remain as they were, and we have the picture produced not only in different lights and shades, but also in different depths, the solution being eaten into by the process. When the plate is prepared to this point, there is poured upon it a preparation of gutta percha, which, being kept under pressure for a short time, receives the reverse image of the photographic picture. This is now prepared for the voltaic battery by being simply rubbed over with fine black lead, and it being placed in connection with the trough, copper is precipitated on the plate, which receives an image the reverse of the mould. Then by the ordinary electrotype process another plate may be obtained, from which copies may be primed.