COPPER, INTENSIFICATION WITH A process for intensifying gelatine negatives. A solution of bromo-iodide of copper is prepared as follows : Copper sulphate . zoo grs. 76 g.
Water . . . 3 oz. r,000 ccs.
When dissolved, add with constant stirring the following, which must also be dissolved : Potassium iodide . 8 grs. 18.2 g.
Potassium bromide .20 ,y ,, Water . . I OZ. 1,000 ccs.
A slight precipitate of iodide of copper of a deep yellow colour forms ; this is allowed to settle and the clear part poured off for nse. The fixed and washed negative is placed in the above until bleached and of a canary-yellow colour, from five to fifteen minutes being usually required. The solution may be used repeatedly if strengthened occasionally with a few drops of a mixture made by dissolving 12 grs. of iodide and 36 grs. of bromide in 2+ oz. of water. After bleaching, the negative is washed well, and dark ened by placing in a strong solution of sodium sulphite to which a few grains of silver nitrate are added. Good results may also be obtained
by darkening with 21 hydroquinone developer. The colour of the resulting negative is strongly affected by the solution used for darkening after bleaching. The above usually gives a reddish deposit which is very non-actinic ; rodinal a brown image, and the sulphite-silver a darker one. Variations in colour when hydro quinone is used may also be obtained by altering the proportions of sulphite and hydroquinone Both the bleaching and the darkening must be done in daylight ; the-stronger the light the better and quicker the results. After darkening, the intensified negative is well washed in water and finally dried. The process may also be used for slides and bromide paper. When used for prints, the paper turns blue when bleaching, owing to the formation of iodide of starch, but the colour disappears when the hydroquinone is applied, and the colour of the print is usually a good brown.