CUTHBERT BEDE, B.A. * * * * * PHOTOGRAPHIC CORRESPONDENCE. _Photographic Engraving._--I inclose a copy of a little book for your inspection, which is remarkable only in this, that the illustrations are produced by photography. The general theory of the method is this: a piece of glass is covered with a uniform thin coating of some substance, so as to be opaque or semi-opaque (the substance should be light coloured), and a design is etched on it with a needle. From this _negative_ positive pictures are printed photographically. As to details, the prints of the mice (p. 46.) and the cat (p. 37.) are from a glass coated with iodized collodion rendered sensitive, exposed to faint light for a short time and developed. In this method, the glass should be heated; and the collodion _burnished_ with the hand, to make it adhere well.[5] The owl (p. 22.) and the stork (p. 10.) are from a glass coated with iodized collodion "rendered sensitive" only, and not developed so as to be only semi-opaque. On this high lights were put with opaque white, and darks were etched out. This has the effect of a tinted lithograph, but requires much more care in printing than the former method, in order to hit the right tint; so much so, that I have usually printed the stork faintly so as not to show the "tint" at all. The frontispiece is from a paper negative, a method much more troublesome and tedious than either of the others, both in preparation of the negative and in printing. I have lately tried gilt glass to etch upon. This would be excellent, were it not most painful to the eyes. And more than two years ago, I prepared a negative by painting whites with water colour on transparent glass with moderate success. I have recently received from Rome a positive printed from a negative on smoked glass, the subject being a mule's head. Of all the methods I have tried, the best is the first mentioned; and it seems to me easier than any species of engraving. Query, What is the best coating for the glass; and what will be the cost of printing on a great scale, as compared with woodcut, lithograph, &c.; in which must be included the cost of the skilled workman which will be saved by this method? HUGH BLACKBURN. [When we add that the work referred to is an edition of _The History of Little Downey_, that the prints in it are executed by a lady, and printed at home by the photographic process, and that a limited number of copies may be had on application to Messrs. {629} Constable and Co. of Edinburgh, the sale being for the benefit of the Glasgow Ragged School, we have no doubt many of our readers will be glad to secure copies, and help to forward the good work which its publication is intended to promote.] [Footnote 5: This method was suggested to me by Professor Maconochie, who indeed prepared the glass on which the mice were etched.]