SearchAbout This SiteTreatment ForumVideo clipsGalleryScienceLibraryTechnology

Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9

Chapter XXXI.
MANIPULATION OF POSITIVE PRINTING.

Preparation of Salted Paper.

FOR sensitizing paper and for toning, washing, and fixing, we require either porcelain or gutta-percha dishes of an appropriate size. These can be had of the city dealers, of any size that may be needed; those of gutta-percha are the best for large operations. The photographic-ware baths may also be used for these purposes, and are to be recommended on account of their cheapness.

There are several kinds of paper in use, such as Saxony paper, French paper, and English paper. There is a difference in the surface of paper, that is, there is a right side and a wrong side. The smooth or right side is the one which receives the sensitizing materials; it can easily be distinguished from its opposite or wrong side. Salted paper may be either arrow-root or albumenized paper.

Plain Salted Paper.

Make a solution as follows

Salting Solution. Formula No. 1.
Chloride of ammonium, 100 grains.
Distilled water, 10 ounces.
Formula No. 2.
Chloride of ammonium, 100 grains.
Distilled water, 10 ounces.
Gelatine, 10 grains.
Formula No. 3.
Chloride of sodium, 40 grains.
Chloride of ammonium, 60 "
Citrate of soda, 100 "
Gelatine, 10 "
Distilled water, 10 ounces.

Dissolve the gelatine in warm water, then add the solution to the chloride and water, and filter into the porcelain or gutta-percha dish. The mixture in each formula is filtered before use. The object of the citrate is to give a slight rose tinge to the middle tones.

The sheets of paper are now prepared as follows:

Fold back each corner of the sheet so as to form a lip by which to hold it; these lips are from the smooth or satin side backward to the wrong side. Then taking the lip on the right-hand farther corner between the first finger and the thumb of the right hand, and the. lip on the left-hand corner between the thumb and the finger of the left hand, raise the sheet, bend it into a curve, and lower the middle part upon the surface of the salting solution; now lower the right hand gradually so that the farther side of the sheet rests upon the fluid; and then lower the left hand in like manner, until the whole sheet swims uniformly upon the surface. The next thing is to see that there are no bubbles beneath the sheet. With a glass rod in the right hand raise the farthest right-hand corner with the left hand, and if any bubble becomes visible break it up with the glass and moisten the paper where the bubble existed, and proceed in this manner with one half of the sheet. Next, holding the glass rod in the left hand, raise the nearest left-hand corner, by the lip, with the right hand, and remove all bubbles from the other half. When these are all broken up, and the paper is moistened on the parts where they existed, the sheet is lowered on the fluid and left there for three minutes. The operation of removing the bubbles is the work of a moment. You have to learn the knack of floating the sheets on the salting solution without soiling the back of the sheet, that is, without getting any of the fluid on this side. If the two sides of the paper are equally smooth, that part which is not covered with the salting solution is marked in one corner with a pencil or stamp-mark. After the expiration of the three minutes, each sheet is raised in the following manner. The lips will have sunk down on the surface of the fluid; with the glass rod in the left hand raise the nearest right-hand corner, seizing this lip with the thumb and finer of the right band, raise the sheet gradually. Laying aside the rod, seize now the nearest left-hand lip with the left hand and hold the hands apart as far as the paper will permit, and the left hand more elevated than the right, allow the sheet to drain into the bath. Now letting the right-hand corner go, with a pin fix the upper left-hand corner to the wooden partition or slip of wood for this special purpose. If the sheets are large, pin also the upper right-hand corner in like manner, to prevent the sheet from curling upon itself whilst drying.

Remove the accumulating drops of salting fluid from the lowest corner, and then let the sheets dry. After this operation the sheets are piled, with the unsalted sides downward, one upon another, and a smooth board placed above and below the pile, and submitted to pressure until required for use.

Preparation of Albumenized Paper.

Albumen can be used either pure or diluted. With pure albumen the prints are very brilliant, but the paper is not so easily prepared. Take, for instance, the whites of twenty eggs, taking care to separate the yolk thoroughly, and place them in a graduated measure. Remove all the germs with a glass rod, and ascertain the number of ounces. Afterward pour the crude albumen into a clean basin, and add for every ounce ten grains of chloride of ammonium dissolved in the least quantity of distilled water. Beat the mixture into a thick, white froth by means of an egg-beater, and allow it to stand for ten minutes; then remove the froth with a fork, and throw it upon a clean hair-sieve. Proceed in like manner with the residual fluid, until it has been completely converted into froth and strained through the sieve. Now leave the albumen to stand for a day or so, well covered up from dust; after which filter through a piece of sponge, and again allow the mixture to settle for a couple of days, and then pour off the supernatant liquid portion from the settlings into the porcelain or gutta-percha dish for use.

The paper, as usual, must be of the finest quality, and marked or stamped on the back, before floating. Much more care is required in the successful management of laying the paper on the salted albumen than upon the plain salting solution, for bubbles are more likely to be formed, and are less easily removed than in the former preparation. Besides this, if the paper be dry, and the weather also very dry, the albumen does not attach itself easily to the paper, and in this case, although a sheet has been thoroughly floated, and without bubbles, the upper part of the sheet, when hung up, allows the albumen to flow off, so that the film on the upper part is much thinner than on the lower part, and a number of irregular marks and curves are apt to be formed on the lower part,. To obviate this, the sheet is suspended by its broadside, by which the distance between the upper and lower side is the least possible. The time of salting in this bath is from two minutes and a half to three minutes. Of course in all cases the time has to be reckoned from the moment the sheet lies uniformly and without bubbles on the surface of the solution.

In every operation of this nature it is well to have systematic arrangements. For this purpose I recommend the photographer to proceed as follows in the preparation of his drying-chamber. On the side of the room, behind the salting solution, and at an elevation of the eyes of the individual, screw on a slip of wood a couple of inches wide and the length of the room. Supposing then the sheets are twenty-two inches long, then bore two holes twenty-one inches apart through the slip of wood; into the apertures insert corks, fitting firmly, and projecting about half an inch from the surface of the wood. Into the center of each of these corks insert the eye end of a steel needle inclined slightly upward. The sheets when raised by the two interior corners, and after draining, are hooked by the two upper corners upon the projecting needles, which, before their insertion into the corks, have to be varnished to prevent rusting and other troubles. When several rows of sheets have to be dried consentaneously the uppermost slip of wood must be the thickest, as, for instance, three inches, if there are three rows, one over the other; the second, two inches; and the last, one inch thick.

In proportion as the albumen accumulates on the lower border, it is removed with bibulous paper, until the papers finally are dry. They are then taken down and planished between rollers or otherwise, and piled away.

Preparation of Arrow-Root Paper.

Cut out a board a trifle less in length and width than the sheet of paper; fix a sheet at a time by a pin at each corner of each edge, folding the edges of the paper down over the edges of the board. Then, with a very fine, soft and moist sponge cover it over smoothly, longitudinally and laterally with the following salting mixture

Formula.

Chloride of sodium, (common salt,) 5 drachms.
Citric acid, 4 grains.
Distilled water, 19 ounces.

Dissolve and filter. Then add four drachms of arrow-root, rubbed with cold water into a cream, so that all lumps have been thoroughly broken up and saturated. Boil the mixture in a glass or porcelain dish, taking care to stir it all the while. When it is cold, and the scum has been removed, it is ready for application with the sponge. By means of a glass triangle or glass rod, all ridges or asperities may be removed, and the paper is then suspended, as before directed for albumen-paper. Arrow-root paper is well adapted for large portraits, and even for large landscapes; for smaller picture, where more fineness of grain and sharpness are required, albumenized paper is by far the best. All the papers, prepared as directed, will keep, but they are best when fresh.

Sensitizing Bath.

The preparations for sensitizing are divided into two classes, one containing essentially nitrate of silver, and the other ammonio-nitrate of silver; these are subdivided by differences in the strength. The ammonio-nitrate of silver solution is certainly much more sensitive than the plain silver bath; the great drawback has been the blackening of the solution by use, for which several remedies have been proposed. Whichever bath is used, its strength has to be maintained at its original point by the addition of fresh silver every time it is used, for the bath soon becomes impoverished by the floating of paper for printing. The sensitizing solution must always be slightly acid, in order that the whites may be thoroughly preserved.

Formula for the Plain Silver Solution.

Nitrate of silver, 2 ounces.
Rain-water, 12 ounces.
Nitric acid, 2 to 3 drops.

The paper to be sensitized in this bath is prepared exactly in the same manner as for floating in the salting solution; the corners are turned back, and then, seizing two opposite corners and bending the paper into a curve with the middle and salted part downward, it is lowered into contact with the fluid, while first one end is gradually let down and then the other, taking care afterward to remove all bubbles with the glass rod, by first raising one corner and then the other. Previous to use, the bath ought to be always filtered from innumerable little particles and scum that accumulate on its surface. By means of an argentometer the strength of the bath can easily be maintained at a given point, namely, at about 70 grains to the ounce of water; and by the application of test paper, it can be ascertained whether it be acid or alkaline, and thus corrected. I will repeat, the bath must be

Slightly acid.
Filtered every time it is used.
Its strength maintained at 70 grains to the ounce.

The papers are floated on the fluid for five minutes, then raised, allowed to drain, and hung up on varnished steel needles inserted into corks in a line over the gutter alluded to in a former part of this work; or if such a contrivance be wanting, the silver solution is removed from the pendent corners by blotting-paper, which is afterward thrown aside on a special heap for reduction. The bath by use will become discolored; in such a case, throw in a small quantity of solution of common salt by degrees and shake well. This will remedy the evil after filtration, but it removes also a considerable quantity of silver, which has to be replenished. The black residue, together with the precipitated chloride of silver, is preserved with all other refuse silver for reduction.

Formula for the Ammonio-Nitrate Silver Solution.

Nitrate of silver, 2 ounces.
Rain-water, 8 ounces.
Alcohol, 1 ounce.

Dissolve the silver in six ounces of water; then separate two ounces of the solution, and add ammonia to it, until the precipitate of oxide of silver first formed is redissolved. This solution is then mixed with the alcohol, and the remaining silver solution and water. By the addition of ammonia decomposition takes place, oxide of silver of a brown color is thrown down, and nitrate of ammonia is formed; an additional quantity of ammonia then dissolves the oxide, so that the solution contains nitrate of ammonia and solution of oxide of silver in ammonia. When this part is thrown into the remaining solutions, oxide of silver is again precipitated; the final solution therefore contains free oxide of silver, and solution of oxide of silver in nitrate of ammonia and alcohol. The alcohol prevents the solution of the albuminous film and discoloration probably.

The papers are floated in this bath not more than a minute; half a minute I find in most cases to be sufficient. But there is this caution to be observed: if the papers when removed from the bath appear streaked with oil, it is well to rub the fluid gently over the whole surface with a tuft of cotton wool. The bath can be filtered, but in that case the same filter has to be used over and over again, because the oxide of silver is gradually taken up and dissolved by the ammonia liberated during the operation. I prefer, however, not to filter the bath, but after use to keep it in the stock-bottle, together with the residue of oxide of silver. When about to use it, it is carefully decanted into the dish, and after settling, a small sheet of paper is drawn over the surface to remove any particles that might be left. The strength of this bath, like any other, has to be kept up by the addition of crystals of nitrate of silver; fresh alcohol and ammonia are added from time to time. The albuminous film is not injured by this solution; the time of floating is much shortened, and although the strength of the solution is higher than that of the preceding, no more silver is wasted or consumed in the operation, because the picture is maintained on the surface of the film, owing either to the diminution of the time of floating, or to the induration or coagulation of the albumen, or to its dryness and consequent impermeability in so short a time.

Fuminating Process.

The advantages of the ammonio-nitrate sensitizing solution are attained by subjecting the sheets of paper, already sensitized by the plain-nitrate of silver solution, to the fumes of ammonia. The modus operandi is as follows: Float the papers for four or five minutes in the first bath, containing from sixty to seventy grains of nitrate of silver to the ounce of water, and allow them to dry as usual. This is the first part of the process.

Next prepare the fuminating box or chamber. Where the quantity of work to be clone is not very extensive, a box three feet long, two feet wide and two feet deep is first constructed. On either side and five inches from the top apiece is cut out, leaving the two ends projecting five inches above the two sides. Construct next on either side a shallow box of the same length as the original one, five inches deep, and two feet wide, and having only three sides. These are fastened by screws to the large and middle box, in such a manner that the open side, fits exactly where the piece has been cut out, forming as it were two shelves. By means of triangular supports these shelves are held in a firm and horizontal position, and give an appearance to the box, when regarded from the end, of the letter T. On each end of the deep box, as well as on each side, on a level with the lateral shelves, screw on four narrow slips of inch stuff, on which can rest a board three feet long and two feet wide; this board, therefore, in its place covers the middle box like a lid. When it is in its place, screw down a small piece of wood on either end of one side, so that it can not slide too far. This lid has a sliding motion by means of an iron rod in the middle of one side, lying horizontally, and passing through an aperture in the side of one of the shelves, so that it may be made to close the top of the box or open it when required. On the top of this T-shaped cavity, there are three doors, each three feet long and one foot ten inches wide, opening by hinges as follows: At a distance of one foot ten inches from either side on the top of this cavity screw on a slip of wood two inches wide; to these slips the hinges are all fixed, so that each lateral door opens toward the middle, and lies when open upon the middle door; whereas the middle door opens toward one side and lies upon the side door. It is intended that one door alone is to be opened at a time. The wood of which these doors are constructed must be soft, so as to allow the insertion of small tacks or pins. This is the fuminating apparatus.

The sensitized dried sheets or pieces of paper are fixed upon the inside of each door by sticking a pin obliquely into each corner, with the albumenized surface downward when the door is shut. At the bottom of the deep box place a plate, containing a drachm or more of ammonia. In winter a pan of warm sand may be introduced, with the plate over this in order to increase the evaporation. The sliding door all this while is open. When each door is covered with sheets, or with as many as are required, close them. It is evident that the fumes of the ammonia will soon fill the whole of the interior, and will thus come in contact with the surface of the silvered paper and produce a decomposition of the nitrate of silver into oxide of silver and nitrate of ammonia. After the paper has been exposed for about ten minutes, the sliding door is closed by pushing it forward with the iron rod until it juts against the small pieces of wood on either end of the opposite shelf. By this means the fumes of ammonia in the body of the fuminator are excluded front the air, and only that portion escapes which lies on the shelves. The fuminated papers are then taken out and pinned by one corner on the corks, in order that all superfluous ammonia. may escape, when they will be ready for printing. It has been asserted that there is a great saving of silver by this process; that the film is much more sensitive to light, and consequently the time of printing is shortened, and that the tones are more brilliant.


Home ~ Library ~ Science ~ Technology ~ Gallery ~ Video ~ Forum ~ About ~ Search