OTHER METHODS OF BLOCK :MAKING.
In the albumen process, a zinc plate is first rubbed with fine pumice powder, and etched to a matt, surface in a bath of nitric acid and alum. It is then coated twice with a biehromated albumen solu tion, and dried on a whirler at a gentle heat. After exposure under the negative in the usual manner, the plate is rolled up with a thin film of transfer ink. The turpentine is allowed to evaporate from this, and the plate is then immersed in water and gently wiped with a moistened piece of cotton-wool ; when, if the ex posure and other factors have been cor rect, the surplus ink will come away, leaving only the image. The plate is now rinsed, dried, and dusted with powdered asphaltum, or resin, or with a mixture of resin, asphaltum, and pitch. After the surplus has been brushed off, the plate is held over the stove until the dull surface of the image becomes glossy. When the plate is cool, etching may take place, a nitric acid solution being employed as Purified bitumen... ... 150 grs.
Chloroform Benzole 2 ozs.
Oil of lavender ... 3 minims.
The bitumen is first dissolved in the chloroform, the other ingredients being then added. Coating is done with a before described, but of rather greater strength. A red powder known as " dragon's blood " is sometimes used in stead of asphaltum in this case a stiffer ink is required, known as " American etch ing ink." The powder is brushed on as
before, and the plate heated till the image assumes a deep brown colour. In a modi whirler. It is usual to dust the negative with French chalk to prevent the bitumen sticking to it during printing. Develop ment is accomplished by flowing over with turpentino, aided, if necessary, by gentle rubbing with cotton-wool. When develop fication of the albumen process, known as the blue process, the plate is sensitised with biebromated albumen, exposed under the negative, and flowed over with a special solution of aniline violet, chloro form, benzole, and alcohol, with mastic or asphaltum added as a resist. When the solvents have evaporated, the plate is de veloped in water, and, after drying, may ment is complete, the plate is washed under the tap to remove the dissolved bitumen, together with any greasiness or scum. After drying, any retouching is done, the plate being then heated to about. 150° F., and allowed to cool. It is next etched for one minute in nitric acid, per cent., rinsed, dried, and smeared over with thick guru. When this is dry, be etched at once with the nitric acid bath.