In the chapter on Development (pp. 18-31), full instructions have been given for the processes of Alkaline Pyro and Ferrous Oxalate development, but latterly Hydro-quinone or Ouinol has come to the front as a reducing agent. It is met with in commerce in grey or buff crystals, or brilliant needles of a slightly greenish-yellow hue : it is soluble in water about 1 in 30 more soluble in alcohol and glycerine. When exposed to the air it soon absorbs oxygen darkening in colour, and when kept in solution in water darkeas also to a deep reddish brown. It is closely allied to Pyrogallol or Pyro in chemical composition. To Captain Abney belongs the credit of having first introduced this re agent to the photographic world, and for some time it was considered but a curiosity, and was from its high price prohibited from coming into general use. Numerous experiments, however, and a great reduction in price, led to its being more generally used. At first the results were extremely disappointing, because the best method of using it was not known; with ammonia as an accelerator but poor results were obtained; but with the carbonates of potash and soda better results were given, but its action was extremely slow, development often being prolonged thirty or forty minutes. But when the Alkaline Hydrates were used, its value was at once recognised and it now holds a place almost if not equal to Pyro. It is essentially a beginner's developer as it allows great latitude of exposure, and may be used for any and every brand of plate or film, and is likewise useful for Bromide'and Alpha Papers and Lantern Slides. The following formulae are given as typical of the innumerable developers recommended. The first is the one we use personally, and is the one we have found, after numerous experiments, to be the most satisfactory for negative work: -

Stock Solution of Quinol. Quinol ... ... ... ... 150 grains.

Sodium Sulphite......... 150 „

Sulphurous Acid......... 15 minims.

Distilled Water to make 10 ounces of solution.

Stock Accelerator.

Sodium Carbonate (pure) ... 1.300 grains.

Potassium Hydrate (Caustic

Potash in sticks) ...... 150 „

Distilled Water to make 10 ounces of solution.

For use, mix equal parts and dilute with twice or three times the quantity of water. One drachm of each with six drachms of water will be found sufficient for a quarter-plate which has received a normal exposure. If the plate has been over-exposed, or where over-exposure is known to exist, about 1/8 grain of Bromide of Potassium, or one drop of the Bromide Restrainer (p. 76) should be added. For under-exposure, dilute with twice the quantity of water, or soak the plate first in the diluted accelerator, and then add the Hydroquinone solution after a minute or two.

Dr. Herklots Vos strongly recommends the following, which will be found a good formula also: -

Solution 1

Quinol ............ 4 grains

Sodium Sulphite ... ... ... 24 „

Distilled Water ......... 1 ounce

Solution 2

Potassium Bromide ...... 60 grains.

Distilled Water to make 10 drachms of solution.

Solution 3

Potassium Hydrate ...... 2 ounces.

Distilled Water ......... 1 „

For normal exposure add five drops of No. 2 and No. 3 solutions to one ounce of No. 1 and allow development to continue for some few minutes, then add another portion of No. 3 to obtain the required density. For underexposure reduce the quantity of No. 2 solution to two drops, and gradually increase the accelerator No. 3; for over-exposure increase No. 2 to ten drops to the ounce. The above quantities are for a quarter-plate. The following is that recommended by a well-known firm of plate makers: -

No. I

Quinol ... ... ... ... 160 grains.

Sodium Sulphite ... ...... 2 ounces.

Citric Acid ... ...... ... 60 grains.

Potassium Bromide ... ... 30 „

Distilled Water ......... 20 ounces.

No. II

Sodium Hydrate......... 160 grains.

Distilled Water......... 20 ounces.

For use mix equal parts of each.

The above formulas will be found all that can be desired for negative work; but for positives, either on paper or on glass as transparencies, the following will be found very effective for black tones: -

Stock Solution I

Quinol ............ 120 grains.

Sodium Sulphite ... ... ... 360 ,,

Sulphurous Acid ... ... ... 18 minims.

Distilled Water to make 8 ounces.

96 HYDROQUINONE OR QUINOL DEVELOPMENT.

Stock Solution II

Sodium Carbonate ...... 960 grains.

Potassium Hydrate ...... 120 „

Potassium Bromide ...... 16 „

Distilled Water to make 8 ounces.

Mix in equal parts, and dilute with three times the quantity of water. The following will give a good purple tone to transparencies on glass, and brownish-fawn to Bromide paper: -

Quinol ... ... ... ... 2 grains

Ammonium Carbonate ...... 24 „

Ammonium Bromide ...... ΒΌ „

Distilled Water .......... 1 ounce.

Mix immediately before using.

In using Quinol as a developer there are one or two general principles which should not be lost sight of. Absolutely clean dishes must be used; any dish which has been used for pyro is unsuitable, and will stain the negative. The best results in negative work are obtained by using fresh developer for each plate, but the old developer need not be thrown away but may be placed in a separate bottle and use 1 for over-exposed plates. For positive work, fresh developer for every plate or print is not so much a necessity, an old developer working well for three or more plates. Negatives and positives should be well washed after developing and prior to fixing. The Hypo or Fixing Bath should not be allowed to get very discoloured or stains will ensue. And lastly, all plates whether negative or positive, should be cleared by the clearing solution recommended on page 29.