CHAPTER III.PHOTOGRAPHIC MANIPULATIONS.

The chemicals being prepared, they must be placed in the dark-room; the collodion bottle should be placed on a convenient shelf close to the door, and on a handy peg hang a broad camel’s-or badger-hair brush, for dusting the clean plate just previous to coating it with collodion; the brush must not be used for anything else upon any pretence whatever. The silver bath must be kept, both in use and out of use, in some convenient corner, where there is no risk of getting any other chemical splashed into it. For a bath holder a deep 15 by 12 porcelain or papier maché dish, with a wooden or stout cardboard lid, should be provided, and this dish must always be thoroughly washed, and wiped dry with a clean damp leather (kept for the purpose), both before use and after pouring the silver solution back into its bottle or jug. Or, if the upright form be preferred, be sure and have it large enough.

The developer should be placed on a shelf, on the right of the sink, the developing cup close by.

The fixing or clearing solution should be kept in an upright bath of glass, porcelain, or ebonite.

The intensifier No. 1 may be kept in a flat dish, or in an upright holder, at discretion; but if in a flat dish, the solution should be poured back into its bottle, after each day’s work.

Keep the intensifier No. 2 in a stoppered bottle close to the sink.

The water varnish also is kept in a bottle or jug.

On a shelf close to the collodion, the polished or albumenized plates may be stacked, with the clean or prepared side facing the wall.

A pneumatic holder for attaching to the back of the plate during the operation of coating with collodion will be found very handy.

Of course, it is thoroughly understood that there is a sink in the dark-room, and a good water supply is indispensable.

Then, again, the window through which the light is transmitted, must be{25}covered with a non-actinic medium, such as two thicknesses of golden fabric, or one of canary medium; do not stint the amount of light, but have as much as possible, so long as it is non-actinic.

Fig. 2.

No arbitrary plan for the dark-room need be followed, but the novice will find the annexed plan useful to him in contriving for himself. It is self-explanatory.

Everything being in readiness, we will now proceed to make a line negative, reserving a description of half-tone work to follow.

To begin: wash the bath holder thoroughly, and wipe it dry, then pour into it sufficient silver solution to make the depth about half an inch; dust the inside of the cover, and put it over the dish; now take a clean glass plate, if it be polished, see that it is edged with India-rubber, and if albumenized, be sure and clean the back—and attach it to a pneumatic holder; then with a broad camel’s-or badger-hair brush (kept for this purpose only) remove any particles of dust, back and front; now hold the plate in a horizontal position and pour upon it, toward the right hand corner furthest away from the body, a little more collodion than it is judged will be sufficient to cover it; let the collodion run to the corner, then incline the plate to the left, and the collodion will run into the upper left-hand corner. Now by inclining the plate toward the body the collodion will flow into the lower left-hand corner, and thence it is guided into the funnel placed in the bottle prepared for its reception; during the time that this surplus is draining, the plate must be gently rocked sideways, so that the lines formed by the collodion, in draining, are merged, leaving the film quite homogeneous. As soon as the collodion ceases to drip, release the plate from the pneumatic{26}holder, and touch the lower ridge of the collodion; if it is quite set, close the door of the dark-room, remove the lid from the bath holder, then—holding the plate in the left hand—with the right hand raise the end of the bath holder, as far as is possible without risking any of the silver solution running over the end of the dish resting on the bench; now lay the plate (with the collodion side up) on the bottom of the dish, then drop the plate into the solution, and, at the same time, lower the end of the dish held up by the right hand, which will cause the silver solution to flow in one even wave over the collodionized surface. This operation must be done with dexterity, as if the silver solution does not flow in an even wave the film will be marked, and, in the case of a half-tone negative, the image will be spoilt. Therefore, it is necessary to see that the plate and dish are lowered simultaneously, so that the solution goes over the collodion film in one steady wave. If the upright bath holder be used, the plate is placed upon the ledge of the dipper, and lowered slowly and steadily into the solution.

The plate will require an immersion of about three minutes for proper sensitizing, and this interval—the bath being covered up to prevent the access of white light—may be utilized to give the final adjustment to the camera, and to see that the drawing or print to be copied is properly in focus.

Use a medium diaphragm in the lens for focussing, and examine the image all over before deciding that it is sharp. Focus by preference about halfway between the centre of the picture and the edges, and then, after moving the rack to and fro until the proper sharpness is obtained, take out the diaphragm and substitute the smallest sent out with the lens; or if the picture to be taken be small and from a large original, then the second, or third, smallest diaphragm may be used.

Now remove the focussing screen from the camera (note that the ground side of the glass has been next the lens) and place the cap upon the lens; close the door of the dark-room, open the dark slide, see that the proper carrier is in it, then raise the plate from the bath slowly, using a silver-wire hook for the purpose. If the solution flows evenly over the film, the plate is ready; but if, on the contrary, the solution flows greasy, then again lower the plate and rock the dish gently for a minute or two. The film being fully sensitized, the plate is carefully lifted out of the solution, both hands holding the plate in such a manner as to avoid touching the film; allow the solution to drain from the plate as much as possible, then lean the plate against the wall, the lower end resting upon a pad of clean blotting-paper, so as to catch any further draining;{27}now with a pad of blotting-paper or papier-joseph wipe the back of the plate as dry as possible; this will prevent stains, and keep the dark slide from rotting by the action of the silver solution.

The plate being drained, lay a piece of thin filtering paper in each lower corner of the carrier, so that the plate will rest upon the filtering paper, which will catch any further drainings from the film, and be a safeguard against stains.

Now lay the plate face down in the carrier of the dark slide, close the door, and fasten it.

The dark slide is now carried to the camera, and inserted in the grooves previously occupied by the focussing screen, taking care that the sliding shutter is next the inside of the camera; when pushed quite home, cover the back with the focussing cloth; pull out the shutter, when the plate is ready for the exposure.

The time of exposure will vary very much with the time of the year, and with the amount of light falling upon the object being photographed. The exact time can be found out only by actual practice, but the operator, in time, by observation, will be able to guess it pretty correctly.

In taking the cap off the lens, be sure that the camera is not shaken, else the picture will be spoilt.

The exposure being made, close the sliding shutter, remove the slide to the dark-room, and close the door; lay the dark slide (with sliding shutter down) upon the bench, open the back shutter, and, placing the pneumatic holder in the centre of the plate, lift it out of the carrier.

Take the plate to the sink, and holding it face up, in the left hand, take the developing cup in the right, and, with a quick motion, pour over the plate sufficient developer to cover the whole film; the developer must go all over the film in one even wave, for any hesitation in this will result in a stain; pour upon the film only sufficient to cover it, and be careful to spill as little as possible into the sink, or else the image will be thin, on account of the absence of free silver washed off by the wave of developer.

Now rock the plate gently, so as to keep the developer flowing to and fro over the film (but keep it there, don’t spill it off) and the image will soon appear, faint at first, but growing gradually darker, the black lines of the drawing being white and the white paper black. If the development be continued too long the lines will eventually be veiled; therefore, as soon as the finest details are out and well defined, place the plate under the tap and allow{28}the water to well sluice the film all over; as soon as it is properly washed, which can be seen by the water flowing evenly over, without greasy looking lines, hold the negative up in front of the window, and examine for spots or stains. If there be any present that at all interfere with the picture, at once reject the negative, placing it in a pan filled with water, to be washed off at leisure. Then start afresh.

The negative being satisfactory, give it another rinse under the tap, and place it in the cyanide bath, where the unaltered iodide will speedily be dissolved. Then it is withdrawn, and well washed under the tap. Whilst the water is washing over the front, rub the back with the fingers or a sponge, and then turn the plate over and allow the water to wash the back also. It is now ready for immersion in the intensifier No. 1, where it remains until the film is bleached almost white. Then it is thoroughly washed, drained, and flooded with a small quantity of intensifier No. 2, which will at once turn the film to an intense black, or if the action does not penetrate through to the back of the film, continue the application until it does; again wash, then place the negative on a rack to drain. When the water ceases to drip, flood the plate twice with the filtered water varnish. Then place the negative on the rack to dry. When dry, it is ready for printing on zinc. The negative may be varnished with a benzole varnish, sold by the dealers under the name of positive or ferrotype varnish. Negative varnish may be used, but unless very thin it is apt to be sticky and render the negative easily marked by the heavy pressure it is subjected to in the printing-frame.

Now lay the finished negative face down upon a piece of clean white paper, when, if it is a good one, all the details of the original will show through, clearly and distinctly; but if any of the details are missing or veiled over, the negative will not do, and another must be made.

This process does not always work satisfactorily, but with care and cleanliness no serious fault should arise.

Sometimes the bath may give what are called foggy images, which are indicated by a veil over the lines. These can often be wiped off with a pledget of cotton-wool. The addition of half a drachm of nitric acid to the eighty ounces of bath solution, thorough mixing, and a rest for a few hours, will end this difficulty. If the dark-room window be not of the proper color, fog will ensue; therefore, the non-photographic experimentalist had better call in the aid of a professional photographer in case of any difficulty in getting clear negatives.

Wilson’s Photographicswill be a profitable investment, as it was published{29}before the advent of dry-plate photography, when the wet process reigned supreme.

At the end of each day’s work the silver solution should be carefully poured into the jug or bottle, and allowed to stand all night; then in the morning, just before using, it should be filtered. The dish also must be carefully washed out and put away in a corner where it has no chance of being soiled.

Such are the manipulations necessary for the production of a negative from a line subject—i. e., a drawing in black and white, in which the whole of the picture is obtained by means of lines, or stipple, or by cross hatching. Flat washes of color not being permissible, all effects of half tones, etc., are obtained by lines, either thicker, or thinner, or closer, or further apart. Such a negative is available for printing from, direct upon zinc, in either albumen or in bitumen, for etching into relief, or for printing from as a lithograph.

THE USE OF GELATINE DRY PLATES IN PHOTO-ENGRAVING.For making negatives for collographic printing either direct or by transfer, gelatine dry plates may be used with as much certainty as the wet collodion, so long as the operator can produce a result giving all the gradations of tone, from the deepest shadow to the highest light; and as there are so many excellent brands of plates in the market, it would be worse than useless to name any brand here as having any distinct advantage over the rest, more especially as the brand that the writer would be inclined to name, would perhaps, by the majority of readers, be classed as a plate that they could not work. This being so, for half-tone negatives, the author leaves the choice of the plate and the manner of working to the operator, contenting himself with saying that the criterion of suitability of a negative for yielding good results by any of the processes treated of in this book, leaving out of the question entirely negatives for line work, etc. (treated of in Parts I., II., and III.), is the same for giving soft, delicate, and brilliant prints, either in platinum, carbon, or on albumenized paper, resting assured that a negative yielding a hard black and white, or a dirty flat print, by any of these three methods, will not give results any different in collographic or transfer methods.

For making negatives for collographic printing either direct or by transfer, gelatine dry plates may be used with as much certainty as the wet collodion, so long as the operator can produce a result giving all the gradations of tone, from the deepest shadow to the highest light; and as there are so many excellent brands of plates in the market, it would be worse than useless to name any brand here as having any distinct advantage over the rest, more especially as the brand that the writer would be inclined to name, would perhaps, by the majority of readers, be classed as a plate that they could not work. This being so, for half-tone negatives, the author leaves the choice of the plate and the manner of working to the operator, contenting himself with saying that the criterion of suitability of a negative for yielding good results by any of the processes treated of in this book, leaving out of the question entirely negatives for line work, etc. (treated of in Parts I., II., and III.), is the same for giving soft, delicate, and brilliant prints, either in platinum, carbon, or on albumenized paper, resting assured that a negative yielding a hard black and white, or a dirty flat print, by any of these three methods, will not give results any different in collographic or transfer methods.

For line work negatives for printing upon zinc, for etching, or for transfers to stone, ordinary gelatine dry plates are not useful, as it is almost impossible to get that freedom from veil over the lines that it is absolutely necessary to have; here the wet collodion is best as it is simplest, easiest, and cheapest.{30}Still there are times when the most ardent wet-plate worker is obliged to confess that the process has its shortcomings, most especially in dull weather, when it is necessary, to get the result required, to give exposures from thirty to sixty minutes; then, what with the plate drying and the want of pluck from the bad light, it is impossible to get a result suitable for the work. In this case the plate called the “Process” plate is a great boon. It is fairly rapid, and gives intense negatives, without veil on the lines.

For making transparencies same size of original negatives, the best plan is to place a large sheet of white paper in front of the copying camera, and rack the lens out of focus, taking care that the white sheet of paper is sufficient to illuminate the full size of the plate. Then in the dark-room place the negative in the carrier of the dark slide, film side up, and carefully dust the surface (also seeing that the back of the negative is clean) with a clean camel’s-hair brush; dust also the film of a gelatine dry plate, and place it face down upon the negative, close the slide, and insert it into the grooves of the camera and expose to the light reflected through the lens from the white sheet of paper for from five to twenty seconds, according to the density of the negative and the intensity of the light; close the lens and the shutter, and remove it into the dark-room for development.

By exposing a plate in this manner there is a far better chance of getting absolute contact between the two plates, as the rays of light are parallel.

For making transparencies for printing upon copper-plates, first of all make a grained negative the proper size, then when this is varnished and touched up, make from it as above a transparency upon a gelatine chloride dry plate, by which process it is more certain to get a suitable result for the process than on a gelatine bromide dry plate.

No formula will be given here for developing these gelatine chloride plates as each packet has full instructions for development which must be followed implicitly.

For developing gelatine bromide dry plates for negatives, or for transparencies, the following, a modification of the Ilford formula, will be found better than using formula where the ammonia and bromide are mixed together.

Solution No. 1.Pyrogallic Acid1ounce.Meta Bisulphate of Potash1ounce.Bromide of Potassium1ounce.Water80ounces.Solution No. 2.Liquor Ammonia1⁄2ounce.Water10ounces.

For a normal exposure equal parts of these are mixed just before using, and for an uncertain exposure begin with two parts of No. 1, one part of water, and one part of No. 2.

THE REPRODUCTION OF NEGATIVES.For the production of suitable collotype prints, the first consideration is the negative, from which the printing surface is to be made. The requirements are, a negative in which all the half-tones, both in the lights and in the shadows, are reproduced in their proper gradations; the lights must not be too dense, or the shadows too clear; the blackest portion of the negative must be that part representing the highest light, and the only clear glass, that which represents the deepest shadow; these negatives may be either wet collodion, or on ordinary gelatine-bromide plates and reversed—i. e., the mirror must be used behind the lens. If it is desired to produce a collographic block from a negative already in existence, and which may not be retaken, then it will be necessary to make another negative. This may be done in many different ways; but whichever way is adopted, the first and most important step is the production of a transparent positive.

For the production of suitable collotype prints, the first consideration is the negative, from which the printing surface is to be made. The requirements are, a negative in which all the half-tones, both in the lights and in the shadows, are reproduced in their proper gradations; the lights must not be too dense, or the shadows too clear; the blackest portion of the negative must be that part representing the highest light, and the only clear glass, that which represents the deepest shadow; these negatives may be either wet collodion, or on ordinary gelatine-bromide plates and reversed—i. e., the mirror must be used behind the lens. If it is desired to produce a collographic block from a negative already in existence, and which may not be retaken, then it will be necessary to make another negative. This may be done in many different ways; but whichever way is adopted, the first and most important step is the production of a transparent positive.

This transparent positive may be made on an ordinary gelatine-bromide plate, or on a gelatine-chloride plate, and then from the transparent positive a negative is made by transmitted light (in the enlarging camera), either the same size, reduced or enlarged in size; or instead of using this class of transparency, by far the finest results can be got by making the transparency in carbon tissue, which can be used for both transmitted light, for enlarging or reduction in size, and it can also be used for contact printing, when the reproduced and reversed negative is required to be the same size as the original.

On page29directions are given for the manipulations when gelatine dry plates are used, so here we will confine ourselves to the production of negatives from the carbon transparency. First of all, procure some carbon transparency tissue, ready sensitized, cut this into sizes at least half an inch larger all round than the negative, then cut a brown paper mask to fit all round the negative, and to protect the margin of tissue from the action of light; this acts as a safe edge to the tissue, enabling it to adhere to the glass support during the operation of development. If it is only intended to reproduce a portion of the{32}original negative, the safe edge may be made by putting the mask just round that portion of the image, but if the whole of the negative is required, put it in a printing frame with a plate glass front, fix the brown paper mask outside the negative, then place the sensitive carbon tissue the black side next the negative film, and put in the backing, and back, and fasten it up. Next expose it to the light for four or five times the time requisite to get an ordinary silver print.

The carbon tissue having been exposed to light for the proper time, it is taken into the dark-room, the edges are turned up so as to form a dish, and pinned upon a small board; it is now coated with thin plain collodion, the surplus being poured into a bottle kept for the purpose, and the board gently rocked to and fro, so as to prevent the collodion running in ridges, or streaks. Now allow the collodion to dry, then place the coated and exposed tissue in clean cold water until it is quite limp, then slide underneath it a gelatinized glass plate a little larger all round than the tissue, bring the gelatinized surface of the glass plate and the collodionized surface of exposed tissue in contact under the water, taking great care not to abrade the collodion; then lift the two out and lay the glass down upon a bench, and cover it over with a piece of thin India-rubber, or mackintosh, or oil-cloth. Hold the cover firmly on the bench with the left hand; with the right use a strong squeegee vigorously. That will expel all the water from between the two surfaces (collodion on the tissue, and gelatine on the glass), and so bring them into absolute contact; now remove the cover, lift the plate and examine the tissue through the glass, and if there are no air-bells between the two surfaces the operation has been successful; but if air-bells are present,at onceplunge the plate into cold water, strip off the tissue, and try again, but be careful to be quick about it, or there is a risk of the tissue absorbing too much water, in which case great difficulty will be experienced in getting it to lie flat upon the gelatinized glass.

The gelatinized plate upon which the exposed and collodionized tissue is mounted is prepared as follows: Glass plates free from scratches and stains, are placed in a weak mixture of hydrochloric acid and water, and rubbed with a clean rag until free from grease and dirt; they are then washed under the tap, and whilst wet are covered with:

Gelatine1ounce.Water20ounces.Bichromate of Potash15grains.

Soak the gelatine in the cold water until it is soft, then melt at gentle heat, add the bichromate, and when dissolved, filter, and coat the cleaned plate two or three times, throwing the surplus away each time of coating; now stand the coated plate on a rack to dry. Any quantity of these plates may be prepared at a time, and used when required. When all the batch has been coated, the rack may be removed into a warm corner, free from dust, until the plates are dry, then expose the plates to the light for at least twenty minutes, when they are ready for use for mounting the exposed and collodionized transparency tissue upon.

After the tissue is mounted upon the glass plate, it is allowed to stand a few minutes, then it is placed in a dish containing hot water (100° F.), and as soon as the tissue compound shows signs of dissolving by exuding from under the paper, lift the paper away, then rock the dish, and, if necessary, add more hot water; then raise the plate and gently lave it with the hot water, until the whole of the soluble pigmented gelatine is washed away, leaving a transparent positive on the glass, which merely requires washing under the cold water tap, and drying, to be finished. Now examine it closely, and if it contains the whole of the details in the negative, and is free from dust spots, it may be put away to dry, but if underexposed, or overexposed, or marred by spots not in the original, then another must be done; but if care is taken to dust the surface of the tissue, and the film of the negative with a camel’s-hair brush before printing, and before collodionizing, and also to see that both the collodion and the gelatine mixture are properly filtered, and that the water in which the coated and exposed tissue is soaked is free from dirt, then there will be no difficulty in getting a perfect transparency.

The transparency being obtained, if it is desired to make a negative larger or smaller than the original, the transparency is placed in the enlarging camera with the carbon film inside, and the negative made the requisite size, either on a dry plate or on a wet collodion plate.

If a negative the same size is required, the transparency is placed face up in the carrier of the dark slide, and the surface dusted; then take a dry plate, and having also dusted its film, place it face down in contact with the transparency, then close the dark slide and remove it to the camera, which should be previously adjusted opposite a large sheet of white paper; now put in the dark slide, draw the shutter, and expose to the sheet of paper, and develop as directed on page30.

By exposing in this manner, instead of direct to the light (day or gas), the{34}rays projected through the lens fall upon the dry plate quite parallel, so securing sharp negatives.

In making reversed negatives for collographic printing when wet collodion is used, it is not absolutely necessary to use the mirror, as they may be made upon polished glass (i. e., not albumenized) dried, then coated with gelatine, again dried, and stripped.

Some brands of dry plates can also be stripped, by first of all, after drying, coating them with India-rubber solution, then with collodion, and soaking in dilute fluoric acid; but great care and patience must be exercised, the preliminary trials being made upon negatives of no particular value.

STRIPPING COLLODION FILMS.Negatives made by the wet collodion process can be easily stripped from the glass support, and in such a condition are extremely handy, especially for printing on collographic plates, or on zinc or copper, as, the film being flexible, contact is more easily secured.

Negatives made by the wet collodion process can be easily stripped from the glass support, and in such a condition are extremely handy, especially for printing on collographic plates, or on zinc or copper, as, the film being flexible, contact is more easily secured.

When it is intended to strip the film, the glass plate must be polished,not albumenized, and after the negative is dried, strips of thick paper are pasted along the four sides of the negative, with starch, or a solution of gum tragacanth; the negative is then placed on a levelling stand and a sufficient quantity of the following warm solution of gelatine is poured upon the plate (which should be slightly warmed first) and spread all over it by means of a glass rod:

Gelatine21⁄2ounces.Sugar11⁄2ounces.Water20ounces.

Soak the gelatine in the water until soft, melt by gentle heat, then strain through two or three thicknesses of fine muslin, and pour upon the plate, using three ounces for a plate 12 × 10; more or less, in proportion for different sizes. The plate must be allowed to stay upon the levelling stand until the gelatine has quite set, then put it on a rack to dry, in a current of cold air, for if heat be used the gelatine will melt.

When the gelatine isquite dry, pass the blade of a penknife all around underneath the strips of thick paper, when the negative film may be lifted away from the plate.

In this condition the negative may be stored away without risk of being broken, the only condition being, it must be kept free from dampness.{35}

Another plan of stripping is to coat the dry negative with a thick solution of India-rubber in benzole, and allow it to dry on a levelling stand; then coat with a thick plain collodion, to which a few drops of castor oil have been added. When the collodion film is quite dry, place the plate in a dish of clean water, strip off the film from the glass, then place the film between sheets of clean blotting-paper to dry, or it may be allowed to dry on the plate.

Old collodion negatives that have been varnished may be stripped, but it is rather a risky operation, and should never be attempted until a really good carbon transparency has first been obtained.

The first step will be to remove the varnish, which is effected by soaking the plate in

Alcohol1part.Ammonia1drachm.

until all the varnish is removed, then rinse in alcohol, wash well under the tap, dry, paste slips of brown paper around the margin, and finally level and cover with the warm gelatine, dry and strip.

THE REVERSING MIRROR.The mirror is a piece of perfectly plane glass, coated on the surface with a thick film of pure silver, and highly polished. This silvered glass must be mounted in a mahogany box, and fitted on the front of the camera, the lens being fitted in front of the mirror, see Fig. 1. This mirror is placed in grooves at an angle of forty-five degrees from the axis of the lens. So situated, it receives the image projected by the lens, and reflects it on the focussing screen, or sensitive plate in the camera. By this means a negative is obtained, which, when looked through with the film between the operator and the glass, will present the image in its proper position, whereas, if the lens be used without the intervention of the mirror it will be necessary to have the glass between the eyes and the film, to get the image in its proper position, and as the generality of photographic negatives are taken without the intervention of the mirror, they are called ordinary negatives in contradistinction to those made through the mirror, which are called “reversed” negatives.

The mirror is a piece of perfectly plane glass, coated on the surface with a thick film of pure silver, and highly polished. This silvered glass must be mounted in a mahogany box, and fitted on the front of the camera, the lens being fitted in front of the mirror, see Fig. 1. This mirror is placed in grooves at an angle of forty-five degrees from the axis of the lens. So situated, it receives the image projected by the lens, and reflects it on the focussing screen, or sensitive plate in the camera. By this means a negative is obtained, which, when looked through with the film between the operator and the glass, will present the image in its proper position, whereas, if the lens be used without the intervention of the mirror it will be necessary to have the glass between the eyes and the film, to get the image in its proper position, and as the generality of photographic negatives are taken without the intervention of the mirror, they are called ordinary negatives in contradistinction to those made through the mirror, which are called “reversed” negatives.

The silver surface of the mirror requires great care and attention to preserve its lustre. If tarnished, it will make the exposure in the camera longer, besides which, the cost of resilvering is too great to allow of the surface being spoiled through carelessness.{36}

At the end of each day’s work, remove the mirror from the box and warm it in front of the fire (not over a gas flame) just slightly, then wrap it carefully in a piece of fine velvet, which has also been previously warmed, then wrap it up in a piece of India-rubber or macintosh cloth, and put it in an air-tight box; by doing this, the mirror, if well silvered at first, will last for a year or two.

If the surface should become tarnished, get a square of very fine chamois leather, and place in the centre a pellet of cotton-wool; then gather up the leather and tie the wool in the centre, making a small globe about an inch and a half in diameter; now warm the mirror, and after dipping the leather globe into fine rouge, proceed to polish gently with a quick circular motion, using little or no pressure—take care in doing this that the mirror, the leather, and the rouge are quite dry, else the silver coat will come away—verb sap.

In purchasing a mirror be sure and get it large enough to take the cone of rays from the lens it has to be used with; for a lens three inches in diameter, the plane mirror should measure about 8 × 31⁄2inches.

The box to hold this mirror should be made square at the side, fitting into the rabbet of the camera front, so that when objects are to be photographed that will do better lying on the ground than when fixed against the wall, the mirror can be placed to look down upon the object.

For silvering the glass, one cannot do better than to quote the directions for working Common’s process given by Major Waterhouse in thePhotographic News.

“The solutions recommended by Mr. Common are three:

(1)Nitrate of Silver1ounce.Distilled Water10ounces.(2)Caustic Potash1ounce.Distilled Water10ounces.(3)Glucose1⁄2ounce.Distilled Water10ounces.

The above quantities are suitable for 250 square inches, consequently, an ordinary copy mirror 8 × 6 would require rather more than two ounces of each solution, and other sizes in proportion.

The caustic potash and distilled water must be quite pure. Ordinary caustic potash will not answer at all. The best to use is known aspure by alcohol.

The glass surface to be silvered is carefully cleaned with strong nitric acid, applied, as recommended by Mr. Browning, with a Buckle’s brush, then well{37}washed in clean water, and after rinsing with distilled water, laid, face downward, in a dish of distilled water until wanted.

Before cleaning the glass, it will be necessary to arrange for supporting it face downward in the depositing dish, so that the surface to be silvered may be quite horizontal, and just below the level of the fluid, which should be about half an inch above the bottom of the dish.

I have generally used a large cork, about four inches in diameter, cemented to the back of the plate, and fitted with three strings, by which it could be suspended in a level position and adjusted to any height by winding the string over a roller placed at a convenient height above the dish. When this arrangement is not available, I fix on the back of the plate two ordinary wide-mouthed bottle corks of equal thickness, in the positions shown in the figure, and to these corks attach thin slips of bamboo running transversely across the plate, and of sufficient length to rest on the sides of the dish, thus:

Fig. 3.

The slips of bamboo give the arrangement a certain amount of spring, by which the height of the plate can easily be regulated, by putting on weights until the surface of the plate is just below the level of the fluid in the dish.

To prepare the silvering solution: A sufficient quantity of the silver solution, No. 1 (two ounces), is put into a perfectly clean glass. Ammonia is dropped in until the precipitate first formed is just redissolved. The same quantity of potash solution, No. 2, as of silver is now mixed in, and the precipitate again dissolved by ammonia. A little more silver solution is then added to produce a distinct turbidity, and distilled water to make up the quantity necessary to fill the depositing dish to about three-eighths or half an inch, and the mixture is then filtered through cotton into another clean glass vessel.

The same quantity (two ounces), of filtered solution of glucose, No. 3, as was taken of silver and potash, is now mixed in, and the whole is poured into a depositing dish (which should preferably be of glass, well cleaned with nitric acid).

The glass plate is then taken out of the distilled water and laid face downward on the silvering solution, being supported, as before described, just above the surface, so that the solution does not cover its back.

Mr. Common places the requisite quantity of distilled water in the dish in{38}which the mirror has been remaining face downward, and then, having lifted the mirror up, pours in the undiluted silvering solution, together with the glucose solution, stirs well together, and then carefully lowers the mirror again into the dish.

Almost immediately after the immersion of the plate, the silvering action begins, and, if things are going on well, a brilliant reflecting surface will be seen at the back of the plate, and in forty minutes, or even less, a good deposit of silver will be obtained. It is usually recommended to stop the action as soon as the silvering fluid appears clear and free from turbidity, but it is not always easy to see this.

After silvering, the plate is well washed, finishing with distilled water, and dried off quickly. A slight cloudiness of the surface may appear, and must be removed by polishing before the mirror can be used. It is better to allow the mirror to remain a day or so before polishing, in order to harden the coating.

To polish the plate, it should be slightly warmed, and perfectly dry, and rubbed very gently in small circles with a piece of very soft and dry chamois leather, afterward using a little jewellers’ rouge.

Mirrors should always be kept in a dry place, and will require repolishing from time to time.

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