WOOD, PHOTOGRAPHIC ENGRAVING UPON. The wood engraver would in many cases derive valuable help from photography, if positive prints could be obtained upon the surface of wooden blocks without injury to the texture of the wood. The following proce,ss, which appears to be the best at present known, is extracted from Photographic Notes, No. 40, and is due to M. Lallemand, a well known wood eno-raver in Paris.
" The invenCor of the process which we are about to describe, M. Lallemand, is a skilful engraver. In consequence of his frequent transactions with the editors of works, in the illustration of which wood engraving is often employed, he endeavoured to solve the problem stated above. But at first two difficulties presented them selves. In the first place it was necessary that the wood should not be affected by the photog-raphie chemicals ; and secondly, that it should not be so coated or varnished with any substance as. to interfere with the operations of the engraver. After more than a year of fruitless experiments, M. Lallemand discovered a process which is free from the above objections, and he has published it in a communication made to the Academy of Sciences, in the following terms : " The surface of the wood (and that only), is submitted to the action of a solution of alum, and dried. The entire block is then
coated with a mixture of animal soap, gelatine, and alum. When dry, the surface which is to receive the image is placed for some minutes on a solution of hydrochlorate of ammonia, and allowed to dry. It is next placed in a nitrate bath, containing twenty per cent. of nitrate of silver, and dried in the dark. A negative, either on glass or paper, is then applied to the sensitive surface of the wood, in a pressure-frame made for the purpose, which allows the progress of the printing to be watched. The image is fixed by a saturated solution of hyposulphite of soda. A few minutes in this solution will suffice. It is then washed for five minutes only.' " The sizing protects the wood from any moisture, and eight months' experience has proved to the inventor that the employment of alum and hyposulphite, instead of loosening the texture of the wood, gives it a great toughness, which is favourable to engraving."