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 II.
PRELIMINARY OBSERVATIONS.

THE art of Photography comprehends all the operations of taking a picture on a sensitive surface by means of light and chemical reagents. These operations are as varied as the different substances on which they are taken, or by which they are taken. In all cases, whatever may be the process, the conditions required in the operation of producing a photographic image are, firstly, a suitable groundwork or receptacle, such as paper, metal, glass, or stone; secondly, a coating of substances called sensitizers, which are very sensitively affected by light and altered according to its intensity; thirdly, chemical ingredients, denominated developers, that act differently upon the parts that have been changed by light from what it does upon the parts upon which light has not acted at all or feebly; fourthly, fixing agents or chemical solvents of the sensitizing agents that have not been changed by light. Other important conditions are comprehended in the light, requiring it to be of a certain intensity, in a certain direction, and in a certain quantity.

The various sorts of matter for the reception of the photographic image have given rise to a variety of processes, whose appellations refer rather to the material employed than to any difference in the actinic principle; thus, on paper, exist a number of so-called processes, as, for instance, printing by direct contact, and printing by development; the plain-paper process, the wax-paper process, the resin process, and the albumen process. On glass are found the negative process, the positive or ambrotype process, and the transfer process. On metal the melainotype and daguerreotype processes and photo-engraving; and on stone, photolithography. In addition to these may be mentioned the card-picture process and that of the stereograph. In reference to the materials used in the sensitized photographic film, or rather to contain the sensitizing ingredients, stand out most prominently; the Collodion processes, wet and dry, the Tannin process, and the Albumen process.

The sensitizing substances most generally used are the salts of silver in combination with organic matter. In the carbon process, as also in photo-lithography, photoengraving, photo-zincography, and photo-glyphography, the sensitive materials are gelatinous or resinous substances in combination with certain chemical reagents that render them insoluble, and in which the solubility, in certain menstrua, is again restored by the agency of light. The salts that have hitherto been used are the bichromate of potassa and the sesqui-salts of iron; the receptacles, asphaltum and gelatine; and the solvents, hot water, oil of turpentine, and oil of lavender. The fixing agents or solvents of the undecomposed iodides, bromides, and chlorides of silver in the collodion, albumen, or surface-sensitized film, on which the rays of light have not acted, or but partially acted, are hyposulphite of soda, cyanide of potassium and sulphocyanide of ammonium. The chemical reagents that either develop the latent image or perfect that which light has already commenced, are the proto-salts of iron, ammonia, gallic and pyrogallic acid, formic acid, and, in the daguerreotype-plate, mercury. Other materials are used in addition to intensity the image already formed by the ordinary developers. The principle involved in the strengthening of negatives is, first, probably by certain electrical decompositions, to produce a deposit oil the shadows formed by means of silver, mercury, lead, or iodine; and secondly, to blacken this deposit by sulphurizing or reducing agents, or by the alkalies.

The great divisions into which photographic operations may be divided are those which treat of negatives and positives. A negative is an actinic impression on glass or waxed paper, in which the lights and shadows are inverted, as also the figures and the different items that form the picture; that is, right becomes left, and left right. The negative is the matrix from which photographic prints are obtained either on paper or other material; these prints are produced either by direct contact of the paper or glass with the negative, or the negative is placed in one focus of a camera, and the paper or glass in its conjugate focus. Such prints or impressions, whether by reflected or transmitted rays, are positives, in which the lights and shades, as well as all the delineations, are in their true and natural position. There is another class of positives in which the shading is natural, but the delineations are inverted; these are exemplified in the Daguerreotype, ambrotype, and melainotype, which are exhibited only by reflected light.

As the present work is intended for practical men, it will be necessary at the very outset to give a list of all the articles and arrangements required in the successful pursuit of the photographic art.

LIST OF A PHOTOGRAPHIC OUTFIT.

1. Glass-house, or room in the garret furnished with a sky-light.
2. Dark room, for sensitizing plates or papers.
3. Operating room, for collodionizing plates, mounting prints, etc.
4. Screens (white, gray, blue, and artistic) for the glasshouse.
5. Lenses, (¼, 1/3, 4/4, etc., stereoscopic and orthoscopic.)
6. Cameras, (for portraits, views, stereographs and for copying.)
7. Ornamental carpets, chairs, stands, curtains, pillars, balustrades, etc.
8. Head-rests, etc., camera-stands, mirrors, brushes, combs, pins, needle, and thread.
9. Washhand-stand. pitcher and basin, soap and towels, clothes-brush and nail-brush.
10. Stove, tongs, shovel, poker, coal or wood-box.
11. Antechamber, suitably furnished with lounges, etc.
12. Show-cases for artistic productions, and cases for chemicals, etc.
13. Collodion, (negative and positive,) acetic acid, nitric acid, citric acid, tartaric acid, protosulphate of iron, gallic acid, pyrogallic acid, formic acid, carbonate of soda, carbonate of lime, (chalk,) chlorinetted lime, nitrate of silver, citrate of soda, phosphate of soda, blue litmus-paper, red litmus-paper, sulphide of potassium, sulphocyanide of ammonium, ammonia, oxide of silver, iodide of potassium, iodide of ammonium, iodide of cadmium, iodine, tincture of iodine, bromide of potassium, bromide of ammonium, bromide of cadmium, bromine, nitrate of uranium, bichloride of mercury, gum-arabic, starch, gelatine, glue, shellac, chloride of gold, acetate of soda, alcohol, ether, distilled water, loaf-sugar, cyanide of potassium, hyposulphite of soda, pyroxyline, sulphuric, acid, rotten-stone, tannin, sesquichloride of iron, oxalic acid, varnish, hydrochloric acid, acetate of lead, caustic potassa, salts of tartar, chloride of Sodium, chloride of ammonium, bichromate of potassa, asphaltum, copal, chloroform, cotton, nitroglucose, mastic, resin, thus, benzoin, benzine, wax.
14. Funnels, filtering-stands, collodion-glasses, developing and fixing-glasses, porcelain or photographic-ware baths and dishes, filtering-paper, plain paper, plain-salted paper, albumen paper, arrowroot paper, tinted paper, resinized paper, wax paper, blotting paper, plate-cleaners, plate-holders, Canton flannel, cotton cloths, silk cloths, brushes, colors, pencils, scale and compasses, magnifying-glass, cases, mats, preservers, glass plates of various sizes, (transparent and ground,) melainotype-plates, black leather, black velvet, black varnish, black paper, scissors, pliers, pens, ink, paper, post-stamps, envelopes, pocket-knife, black lead-pencils, gutta-percha dishes, pails, towels, pitcher, ice-cooler, soft water, focussing-cloths, brooms, hand-brush, diamond, cutting board for glass, shelves for negatives, drawers for mounts, papers, etc., beaker-glasses, wash-tubs, scales, weights and graduated measures, dropping-tubes, test-tubes and rack, evaporating-dishes, crucibles and furnace, tongs, coal or wood, door-mats, hat-stand, artificial paraphernalia, as stuffed birds, beasts, etc., skeletons, vases, printing-boxes, fuming boxes, forms for cutting out stereographs, card-pictures, etc., card-board, mounts of various sizes, spatula, pestle and mortar, India-rubber, lamps, candles, frames for photographs, solar camera and its appendages, solar microscope and accessories, glue-pot, tea-kettle, changing-box for dry plates.
15. For out-door work will be required extra: a small hand-cart and tent, or dry collodion or tannin-plates, wax-paper, graduated tape, saw, hatchet, hammer and nails, negative-holder.