Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 133

This pellicle consists of shreds of dry gelatin containing the sensitive salts.

Fresh directions accompany each packet of the "Sensitised Pellicle."

_The Honey Process._ Let the plate be cleaned, coated, and sensitised in the usual manner; then place it in a bath of distilled water, washing it more or less, as it may be required to be kept for a longer or shorter time. Pour on the plate a solution made of equal parts of honey and distilled water in the same manner as when using collodion; throw away the first portion, and repeat the operation, letting the solution soak in for one or two minutes; pour back the honey solution into its bottle; drain the plate on blotting paper, and keep it in the dark free from dust. The time required for exposure of the plate is about double as long as in the ordinary wet process.

The plate should be soaked in distilled water previous to being developed, in order to soften or remove the film of honey; the older the plate the longer it will require to be soaked, afterwards dip the plate in the silver bath, and develop in the usual manner.

_The Carbon Process._ In this process, the adoption of which is daily increasing, the material employed consists of a layer of gelatin containing carbon, or some other permanent pigment, spread on paper.

In this condition the paper is not sensitive to light, but if it be treated with a solution of bichromate of potash, dried in the dark, and afterwards exposed to sunlight under a negative, those portions of the paper which have been acted upon by the light will become insoluble, whilst those parts that have been protected from it will be soluble. When, therefore, after sufficient exposure, the prepared paper is removed from the negative, a picture the reverse of the negative will have been formed, in which the pigmented gelatin alone remains, and performs the part of the reduced silver in the ordinary photograph.

If the film, after exposure to light under a negative, is soaked in warm water, all the parts which have been protected from the action of the light can be dissolved, and a relief is formed which, when dry, is sufficiently hard to transmit its shape to lead. From the mould or plate thus obtained a comparatively large number of impressions can be taken, either with coloured gelatin or with fatty colours, the well-known Woodbury-type being the most successful of the several processes based on the fact.

=Photographic Varnish.= See VARNISHES.

MISCELLANEOUS RECIPES:

_To Clean Gla.s.s Plates._ (Mr Mayall.) Shake up together alcohol, 30 parts; strong liquid ammonia, 10; water, 40; and fine tripoli, 30 parts. The plates are to be rubbed hard and evenly with b.a.l.l.s of cotton wool dipped in this mixture. Rub again, when dry, with a clean ball of cotton; lastly, dust the back and edges with a clean hog-hair brush.

_To Clean off Collodion Pictures._ This may be done whether they have been varnished or not, by means of a tuft of cotton wool dipped in wood spirit.

_To Colour Photographic Prints._ This may be done variously in water and oils. A simple way is to rub in slowly with a small camel-hair brush a minute piece of dry colour laid upon the part, as of flesh tint for the face, &c. When properly distributed, the paper may be breathed upon, and the tint will not easily be rubbed off. Or it may be carefully coated with gelatin.

M. Minotto has described a plan of colouring on the back of the paper. The picture, being held up to the light, is first faintly outlined, on the reverse side; colours are then laid on, of water or oil, as preferred, on this side. When dry the paper is rendered transparent by a varnish, and the colours will then appear through it with all the delicacy and effect of a miniature on ivory. Good strong writing paper is best for this purpose; the colours must be vivid; and the varnish may consist of Canada balsam dissolved in turpentine, or a mastic varnish may be used, or turpentine and wax, or oil.

_To Remove Stains from the Hands._ The powerfully poisonous character of cyanide of pota.s.sium renders its employment for the above purpose an operation attended with considerable danger. Iodide of pota.s.sium and iodine may both be subst.i.tuted, but the first is expensive, and the second requires considerable nicety in its application, lest a coloured stain be left on the skin. Instead of the above substances, M. Fortin recommends to wash the hands with a concentrated solution of either sulphate or chloride of zinc, to which some acid is added at the same time. He advises the deepest and blackest stains being touched with metallic zinc, whereby the reduction of the oxide of silver or that of the gallate of iron is promoted, and all metallic stains adhering to or penetrating into the skin removed. Since most of the salts of zinc are colourless, and soluble in water, the hands soon become quite clean. They should then be washed, first with pure water, and next with soap and water.

The reader desirous of further information on the subject of photography cannot do better than consult Mr Ernest Spon's valuable manual, ent.i.tled 'Workshop Receipts,' and Mr Hughes' 'Principles and Practice of Photography,' to both of which we are largely indebted. Captain Abney's work on 'Photography,' cannot be too highly commended. See COLLODION, PHOTOGRAPHIC.

=Photographic Waste Products, Recovery of.= We extract the following from the 'American Chemist' for February, 1876. The contributor, Mr. C. A.

Pitkin, A. B., states that the methods given have been collected from the 'Philadelphia Photographer,' the 'British Photographic Journal,'

Hardwick's 'Photograph Chemistry,' &c., &c.; also that they include suggestions by Professor Hill.

1. Nitrate bath, a, recovered; , renovated.

2. Hyposulphite bath.

3. Reduction of silver chloride, oxide, or sulphide.

4. Gold waste, a, recovered; , separated from silver,

5. Paper waste and washings from positive prints.

6. Cyanide solution.

7. Developer.

I. _Nitrate Bath_,

a, _Recovered_.

1. Add solution of caustic potash or lime, as long as there is a brown precipitate. Allow to settle, pour off liquid, and collect silver oxide for reduction; _vide_ III, below.

2. For 1 lb. of silver, add 1 oz. sulphuric acid and 1/2 lb. zinc, and allow to stand two days. Precipitate as chloride, wash eight or ten times by decantation, and dissolve gradually in nitric acid.

NOTES.--Test complete washing by hydrochloric acid. Wash with water till zinc nitrate is removed. If zinc clings to silver wash with hydrochloric acid.

3. Suspend sheet of copper in bath for two or three days.

4. Acidify as nitric acid, precipitate as silver chloride by sodium chloride or hydrochloric acid, and reduce as _vide_ III, below.

5. Immerse in bath two strips of copper attached to the poles of a Daniell's or Smee's cell. Silver deposited on the copper as in 3, above.

6. Add sodium bicarbonate or sodium hydrate. Reduce as 3 below, or if pure enough, dissolve precipitate at once in nitric acid.

7. Concentrate bath, make alkaline by sodium carbonate, and add aqueous solution of oxalic acid neutralised with sodium carbonate. Filter, dry, and fuse with equal weight of sodium bicarbonate.

8. Deposit, either with or without battery, on iron. (Iron can be obtained purer than zinc or copper, and possesses the additional advantage that the iron salts, as iodides, &c., are all quite soluble). Fuse with pota.s.sium nitrate and sodium carbonate.

. _Renovated._

1. Dilute with three volumes of distilled water, expose to sunlight, filter, add sodium carbonate till slightly turbid. Expose to sunlight six hours more, filter, add sodium carbonate till silver all thrown down.

Wash, precipitate by decantation, and dissolve in nitric acid. Filter again, make up to 35 grammes; neutralise, expose to sun a week, and bath is ready for use.

2. Neutralise with ammonia till just alkaline; boil till black; let cool, filter, acidify with pure nitric acid, and evaporate to crystallisation, then fuse. When cool, add distilled water, shake and let stand exposed to light. Filter and add drained crystals. Dissolve and make solution acid with pure nitric acid. Expose again to sunlight, filter, and bath is ready for use.

3. Add pota.s.sium permanganate, expose to sunlight, filter, acidify, put in clean bottles four-fifths full, cork, and freeze in a tray; thaw gradually till ball of ice one-eighth size of bottle remains. This contains impurities to be reduced as III, below. Use rest for new bath at once.

II. _Hyposulphite Bath._

1. Precipitate as silver sulphide by pota.s.sium sulphide. Reduce as III, below, or dissolve in nitric acid.

2. Precipitate by hydrosulphuric acid, and reduce as III.

3. Decompose hyposulphite by waste nitro-sulphuric acid from manufacture of gun-cotton for collodion. Have silver sulphide and sulphur, with sodium nitrate and sulphate in solution. Suspend zinc in solution, then boil two or three hours; wash on filter, dry, fuse with borax and sodium carbonate.

4. Suspend sheet copper in bath.

5. Add hydrochloric acid, which sets free sulphur and precipitates silver chloride. Oxidise sulphur by aqua regia, and reduce silver chloride as in III.

6. Add sodium hypochlorite to the alkaline solution. Wash, precipitate, and fuse with mixed carbonates. This gives sodium bisulphate and chloride as by-products, no sulphur, no fumes.

III. _Reduction of Silver Chloride, Oxide, or Sulphide._

1. Mix with one third weight of colophony. Heat moderately in crucible till greenish-blue flame ceases, then suddenly increase heat, and obtain a b.u.t.ton of metal.

2. Melt with alkaline carbonates enough to cover surface from air; then mix with 75 per cent. of chalk and 4 per cent. of charcoal, and heat.

3. Ignite with nitre on red-hot plate carefully, and in small quant.i.ties to avoid explosion, run down to b.u.t.ton with borax and sodic carbonate.