quarta-feira, 7 de julho de 2010



18 de Maio



No. 1165


London, Saturday, may, 18, 1839

pAG. 314, 415, 316

Fine Arts

Various have been the methodes detailed for the preparation of paper which can be acted upon with facility y the powerful agency of the light from the sun; yet, notwithstanding all that has been written on this interesting subject, the  pratical student in this art finds that great difficulties occur in every department of photogenic drawing.

In the first place, he finds that the paper which he has prepared the preceding evening is by no means equal in its qualities, as sometimes he may have two or three sheets very excellent, so that, when they are exposed to the light, they become in every part of a uniform dark colour; sometimes, on the contrary, he finds that the paper, after it has been similarly acted upon by the solar rays, becomes black over the greater part of its surface, yet numerous white spots occur throughout which detract much from the beauty and effect of drawings made with it; and, lastly, it occasionally happens, that some sheets are not affected by the most powerful light, except, perhaps, at a few points

Indeed, should the paper be good, and the drawings made, yet, without the greatest care in the fixing of them, they may be found to have a ground of an irregular tint, or they may be imperfectly stopped, and even the colour may be altogether removed.

To surmount with certainty these various difficulties, numerous experiments have been performed in every department of the manufacture of photographs, which we shall now describe; first as regards the chemical substances, then the paper, and, lastly, the most efficient stopping solution

The various compounds of silver have been long known to be acted upon powerfully by the solar rays: this property is possessed by far the great number of the preparations of that metal, yet not by all; and upon the former, the effect of light differs materially in its degree of sensitiveness.the two soluble salts of silver with which we are most acquainted, are the nitrate and sulphate, both of which communicate to organic textures and substances made from them a black stain when exposed to light; but these, neither on paper nor in combination with albumen, gelatin, gums, or glutea, have sufficient delicacy to be applicable for the manufacture of photogenic drawings.

The ammonia-nitrate of silver will be found considerably more delicate than either the nitrate or sulphate, and may be used where rapidity of action is not required, particularly as it lessens the trouble, by the application of only one solution to the paper.

The chloride of silver is the substance to which we principally look for the ready action of the solar rays, and the modes of its application to the paper are numerous. It is by itself very insoluble in water, and, on the contrary, easily dissolved by ammonia; but, unfortunately, the ammonia-chloride of silver cannot with good effect be used for the preparation of this paper, and thus we are compelled to form a chloride upon it by a more circuitous process. This object may be effected by the application of either chlorine, chloride of an oxide, chloride of metal, or hydro-chloric acid, first to the paper, and afterwards a solution of nitrate of silver.

When a nearly saturated solution of chlorine is used, it should be applied lightly with a sponge to the paper, taking care that every part is moistened by the liquid : the paper should then be allowed to dry, and the solution of nitrate of silver applied also with a sponge, in a similar way.

This form of chloride is not quite so delicate as some others, and requires a long time to become quite black. It has its advantages from enabling the most highly glazed papers to be prepared with great facility and certainty, and it becomes of a beautiful brown, which is but slightly altered by the stopping agents

The chlorides of oxides, such as the chlorides of soda and of lime, may be advantageously applied in some cases where the chlorine is useful. • • • The chloride of soda, however, must not be used for absorbent papers, such as those used in printing; but with the glazed papers it becomes very delicate and sensitive to light, whether it be applied before or after the solution of silver. The strengtl which was found most useful was that usually employed for medical purposes

The solution of chloride of lime was made by adding twelve grains of chloride of lime to an ounce of water, and allowing any insoluble part to subside. This is found applicable both to printing and to glazed papers, but is more certain when used prior to the nitrate of silver.

The chlorides of metals, as common salt, require more care in their proportions than the foregoing substances ; and an experiment which was tried, shows the absolute necessity of using an excess of nitrate of silver.

A weak solution of nitrate of silver (twenty grains to the ounce) was treated with excess of chloride of sodium, when an insoluble chloride was precipitated ; this was exposed to the direct rays of the sun, without the slightest change ; the supernated liquor was then poured off, and the precipitate well washed two or three times with distilled water, to remove any superfluous salt which might perchance be present; the chloride of silver was again exposed to the light for many hours, when only a slight brown tint was produced. On the contrary, when the nitrate of silver was treated with such small quantities of salt, that part of the solution of silver remained in excess, the light speedily blackened the chloride exposed to its action. • • •  Similar experiments were tried with chlorine, chloride of lime, and chloride of soda, when excess did not prevent the blackening ; but when muriatic acid was used the same phenomenon was observed. • • • Without endeavouring to explain the difference of the action of light under these different circumstances, an important practical inference is to be drawn from them; for if any circumstance prevents the nitrate of silver being in excess, no action will be produced.

The proportions given by Mr. Golding Bird are evidently so designed, that an equivalent proportion of each substance should be used; for although he employs only a twenty-grain solution of nitrate of silver to the ounce, with a twelve-grain solution of salt, yet, by using the silver twice, it becomes equal to the single application of a forty-grain solution. To ensure success, the ratio of the chloride of sodium to the nitrate of silver should be about one to five. As the relative proportions of these two substances are of importance, great care must be taken in the application of the salt in the first place to the paper. A ten-grain solution of salt should be sponged over one surface of the paper, and all superfluous moisture carefully removed by the sponge wrung dry ; the paper ought then to be allowed to dry, but taking care that the salt does not settle in any part, and thereby cause an excess; when the paper is dry, the solution of nitrate of silver is to be applied in a similar way. An advantageous mixture can be made of the chlorides of oxides and chlorides of metals: thus, a very excellent paper may be made by a solution containing ten grains of salt and twelve of chloride of lime to the ounce of water.

Dilute muriatic acid may also be used for the manufacture of the photogenic paper, in the proportion of about twenty-four drops of the distilled acid, S. G. 1.12, to an ounce of water. It may be used either on the glazed or absorbent papers, but for the latter it should not exceed half the strength. The same observations apply to any excess of muriatic acid as were noticed to apply to the floride of sodium. This forms a delicate paper, and becomes of a very even colour.

A more sensitive paper may be prepared by using the bromide of silver instead of the chloride ; but the expense of bromine and its compounds is an objection.

A solution of bromine in water cannot be used in a way similar to a solution of chlorine with any good result, and recourse must be had to the bromide of potassium, of which 12 grs. to the ounce, applied in the way described when treating of the chloride of silver, and afterwards conjoined with a solution of nitrate of silver (fifty grains to the ounce), will be found a suitable proportion.

Other salts may be used besides the chloride and bromide, such as the phosphates, chlorates, &c, but have the disadvantage of not being so sensitive to light. A benefit, however, attends the use of the phosphates, &c, for while any excess of the chlorides must be so carefully avoided, an undue proportion of the latter salts is attended with no inconvenience

The expense of the nitrate of silver renders it desirable to reduce the quantity used ; but if a dark ground is wanted, a smaller quantity than fifty grains to the ounce cannot well be employed.

Having considered the chemical substances which may be used for the photogenic paper, the different kinds of paper, and those suited to each particular preparation of silver, next demand attention.

Papers may be divided into three classes, the bibulous, the absorbent, and the highly glazed papers. Of the bibulous papers, blotting paper and tissue papers are examples; but none of them will be found at all applicable to the purposes of the photogenic art. These papers are made from rags, but there are papers made from other substances, such as old sacking, &c., which possess great strength, as well after they have been moistened as before

The finest paper of this sort is called “double small ends” . That which I employed, when sponged over, seemed to bo equally moistened in every part, and was found well adapted for the intended purpose, as there was not, after being prepared with the solutions, a single spot that resisted the action of light in any one of the sheets. There are, however, disadvantages attending the use of this paper, for it is not so smooth as others more highly glased, and therefore not so well adapted for every description of photographs

The absorbent papers, or the papers used in printing, possess a finer texture than that last described; and when they can be obtained good, they answer very well for photogenic purposes.

Of the various papers which have been tried of this description, a thin paper used for printing newspapers, called “double copy,” was found the best; for the thicker papers, that have much plaster of Paris added to increase their substance and weight, do not answer so well, as they are apt to absorb the solutions unequally. These papers are fittest when the common salt and nitrate of silver are used.

The highly glased papers, or writing papers, require no particular observation, for if either chlorine, chloride of lime, or chloride of soda be used, the colour will be found uniform; and the finer and more highly glazed the paper is, the better will it suit the intended purpose. These will be found advantageous, not only from possessing a smooth and uniform colour, but also from a smaller quantity of the solution of nitrate of silver being used in their preparation, as it is applied only on the surface, and does not penetrate any distance into the texture. For this latter property, paper such as the satin post, may be prepared on both surfaces, should that be deemed advisable

The modes of applying the chemical substances to the paper have been already noticed, and the sponge was mentioned as being the agent employed.

The extent to which the paper should be moistened is, that such a quantity of solution should be used, that it may, as artists term it, “bear out” in every part of the surface; that is, that a slight layer of moisture should appear at every point after the usual absorption has taken place, and that all superfluous moisture is to be carefully removed by a pressed sponge.

After the paper has been prepared, it will be hardly necessary to state that it must be kept carefully from the action of the light.

The mode of making the drawings has been sufficiently detailed in various publications.When prints are to be copied, the printed side must be pressed by a piece of flat glass close to he prepared paper, and exposed to the light of the sun . When drawings of feathers, or other irregular bodies are desired, a piece of the photogenic paper is to be laid upon any yielding substance, as folded linen, flannel, or, what is perhaps better, a layer of sand, or bran; the object is then to be covered with a square of flat glass, and, if necessary, pressed down by weights, and is to be finally exposed to the light of the sun.

The paper will be found to be most rapidly acted upon by the direct rays of the sun, but this is by no means indispensable, as a clear sky is very effectual, and even on a very cloudy day a delineation is produced, only it requires a longer time. The circumstances which appear most to retard the photogenic properties of the solar beam, are those dense collections of smoke which hover over the metropolis when the wind has not sufficient power to disperse the deleterious particles of which they are composed

Most of the modes of preparing the paper, which have been described, are applicable to the camera obscura with a short focus, and those prepared with the chloride of soda, chloride of lime, and bromide of potassium, do extremely well. Its use in this department will for ever be limited, for a portion of an object only can be represented accurately ; as, for every distance, tbe camera requires a different adjustment of its focus, so that to take a landscape, a hundred different foci would scarce suffice. For this reason, it certainly appears that the results of M. Daguerre's experiments must be exaggerated.

The fixing of the drawings after they have been made is completely a chemical action, and requires as much care as the preparation of the paper. The substances that may be employed for this purpose, are dilute muriatic acid, chloride of sodium, hydriodic acid, hydriodate of potash, iodic acid, hyposulphites, sulphocyauate of potash. Before using any of these substances, the drawing ought to be soaked in common water for a few minutes, to remove any excess of the salt of silver; the stopping solution is then to be applied with a sponge to every part of the surface equally.

No particular advantage attends the use of the muriatic acid, but it will be found to stop pretty well when in the proportion of about twenty-four drops of the distilled acid to an ounce of water, but it is not quite permanent. The chloride of sodium, or common salt, is very effectual in stopping any further action of the light, as drawings fixed by this agent have not undergone the slightest alteration from many hours exposure to the brightest sunshine. When the impressions are very dark they do not change colour, but lighter drawings become altered to a yellowish brown; the addition of a little sesquichloride of iron corrects this, and gives a pink tinge to them. The solution recommended by Mr. Bird answers very well, it contains two ounces of salt and one ounce of tbe sesquichloride of iron to the pint of water. The hydriodic acid, and the hydriodate of potash, are also very effective in preventing any further action of the solar rays ; they turn the white parts to a pale yellow, and are very apt, if the solution be too strong, to remove the colour of the dark ground, especially if the drawing had been exposed to the light for only a short time: for this reason, the solution of hydriodate of potash ought not to exceed ten grains to the ounce of water. A solution of iodic acid, fifteen or twenty grains to the ounce, is very excellent for stopping photogenic drawings; it is particularly applicable to delicate drawings of feathers, when it is desirable not to allow them to remain long in the light; and at the same time the contrast of black and white heightens the effect. Care must be taken not to apply too strong a solution, for that is apt to whiten the dark ground, but it never turns it to any other tint.

The hyposulphates of potash and soda have been much used for the fixing of drawings, but, if exposed to the sun, they do not appear quite so effective as the common salt, or hydriodate of potash ; they have the advantage, however, of stopping them a darker colour. The sulphocyanate of potassa is also found to stop these drawings; it changes the colour of the ground to a brown, and has no particular advantage.

The different effects of these several fixing solutions can be turned to good account by suiting the colour of the drawings to the fancy of the artist, or the nature of the subject; and a still greater alteration of tint may be produced by varying the duration of time which the light is allowed to act upon the paper.

Many other chemical substances have been tried for fixing the drawings, but none attended with, success. The following are the principal: — Chlorine, chloride of soda, chloride of lime, tincture sesquichloride of iron, chloride of manganese, chloride of tin, chlorate of potassa, solution of iodine in water and in alcohol, carbonate of potash, hydrocyanic acid, dichromate of potash, biboratc of soda, oxalate of ammonia, fluate of ammonia, benroute of ammonia, succincte of ammonia, phosphate of soda, gallic acid, arsenite of ammonia, sulphite of soda.

Should it from any cause be thought desirable to remove from the paper the colour which it acquired by light, this may be performed either by a strong solution of corrosive sublimate, which will render the paper quite white, or by a strong solution of hydriodate of potash, which gives it a yellow tint. If to the saturated solution of corrosive sublimate a little gum be added, it may be used with a quill pen, either to prevent the action of light, or to make white lines or marks after the action of the solar rays. Drawings may be made with great effect in this way, on paper previously exposed to the sun ; and this is by far the best mode of proceeding, when naturalists or others are desirous of circulating a few copies of any delineation among their own friends; for, as the white parts are exceedingly diaphanous, and the black impervious to light, the drawings made by this means are much more distinct than those made by the ordinary described processes. This mode will be found exceedingly valuable where a few copies of any drawing of machinery are suddenly wanted for estimates of prices or other causes; and the strongest light will never affect the original drawing.

By the common method of making photogenic drawings, should any be imperfect or otherwise damaged, it will be better to expose them freely to the action of the sun; by which means a uniform black ground will be produced, which will be suitable to the use of the corrosive sublimate: and thus any waste will be prevented. A thin paper, which should be slightly moistened before use, is most applicable to this mode of drawing. The photogenic paper may be blackened either by a dilute solution of proto-sulphate of iron or by hydrosulphate of ammonia.

The principal points in every department of the photogenic art have now been described, and if the minutise which have been detailed are strictly followed, and the preparation of silver suited to the kind of paper as here laid down, the student in this interesting and new field of science will be enabled not only to prepare his paper, but also to make and fix his drawings with ease and certainty.

Alfred Smee.

Bank of England, May 14th, 1839.

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