Methylated Spirit...... . 5 oz.
Water.......... 1 „
Hydrofluoric Acid....... 1/4 oz.
Citric Acid......... 1 ,,
Glycerine . . . . . . . . . 1/4 „
Water.......... 8 „
No temporary support must be used nor the enamel collodion, these serving the purpose of preventing enlargement. As soon as the film is loose slip the larger glass support under it, guide into contact and transfer to clean water.
The hot method of varnishing negatives is the best, but the requisite dexterity in distributing the liquid evenly over the plate is not often attained in these days, when the wet-plate process no longer gives one a chance to practise. See that the film is clear of dust, then warm the back of the plate at the fire or a gas-burner until it is nearly as hot as the hands can bear; then, holding it by a corner, pour the varnish on the centre of the plate. By inclining the plate gently coax the flood up one side, down the next till, at the last corner, the surplus may be poured into an extra bottle for refiltration. Heat may be again applied as soon as any streaks across margin and back have been wiped away.
The best hot varnish for gelatine negatives is made by dissolving 2 oz. of orange shellac in a pint of methylated spirit with 1/2 oz. of oil of lavender. An ounce of powdered whiting is then added, the whole shaken up and allowed to settle and finally filtered through cotton wool in a glass or paper funnel.
A good one for retouching on is:
Sandarac ......... 1 oz.
Oil of Lavender........3/4 ,,
Methylated Alcohol........7 „
These may be applied by the brush in the cold state, and dry very quickly. Films may be either brushed or dipped in the preparation and then hung up to drain.
Gum Dammar........ 50 gr.
Benzole ......... 1 oz.
This dries a few moments after application, but does not become hard for some hours unless moderate heat is applied. Another very effective cold varnish for plates or films is made by dissolving 1 oz. of celluloid in 50 oz. amyl acetate. Old film negatives stripped of their gelatine surface may be used for making this varnish.
Water varnish is prepared by pouring a quart of boiling water over half an ounce of borax, and adding by degrees a pound of orange shellac (stirring to ensure rapid melting). If the borax does not suffice to make all the shellac dissolve more is added, a few grains at a time. The solution will keep for a long time, if corked free from dust, and may be used alone; but it is more commonly employed as a cold varnish as follows:
Water Varnish........2 oz.
Ammonia......... 60 minims.
Methylated Spirit.......4 oz.
A practical negative varnish good enough for most purposes, for use either hot or cold, may be manufactured by diluting any good hard spirit varnish procured at oil shops with an equal volume of methylated spirit.