NEW PHOTOGRAPHIC PROCESS.

Globe, Volume XXI, Issue 1714, 18 August 1879, Page 3

NEW PHOTOGRAPHIC PROCESS.

To Mr Woodbury’s inventive ingenuity we owe the plan of producing phosphorescent photographs, which has been tested, and is a practical success. The method he employs is known as tho “ dusting-on” process. It consists in coating a plate with a preparation of dextrine, honey, and bichromate of amm' nia, which, exposed under a negative, becomes hardened, whore it is subjected to the action of light, through tho transparent parts of the negative, remaining tacky where it is protected from the action of light by the denser parts of the negative. After exposure under a negative, the film, as it will be seen, is tacky in the lights of the picture, but herd and dry where light has acted on the shadows. The lights are therefore adhesive and tacky, retaining any fine powder which is dusted in or rubbed into the moist surface. At this point comes in the essential novelty. The powder to bo used must bo a phosphorescent substance. One of the best known and available is sulphide of calcium. A powder of this substance is applied to the image formed on tho adhesive film, and sticks to it in due gradation of the tackiness, as regulated by the action of light which passed through the negative. An image of sulphide of calcium is thus formed, which, the powder being nearly white, is scarcely visible by daylight, but if tho image be submitted for a time to sunlight, or bright daylight, or brilliant artificial light, and then taken into the dark, protects a luminous picture, somewhat startling, indeed, in tho case of a portrait. A variety of substances possess this phosphorescent quality : sulphides of barium, calcium, and strontium displaying it in the most marked degree; fluorspar, carbonnato of lime, pearls, diamonds, phosphate of lime, arseniato of lime, and other substances, all showing in their degree this capacity of absorbing light and radiating it in the dark. The Bologna stone, consisting of sulphide of barium, displays this property in a marked degree. Tho old Italian cobbler to whom tradition assigns the discovery of tho property of this stone and its use, to astonish his friends and neighbours, prepared it by heating red hot with charcoal a piece of sulphate of baryta, found plentifully in the neighbourhood of Bologna. Sulphate of baryta made into a firm paste with gum, or with flour and water, and calcined, will produce tho substance. It should bo kept sealed in a stoppered bottle. The phosphorescent property has been utilised in America for tho production of luminous clock and watch faces, which readily show the hour in the dark. Professor Morton, in tho “Scientific American,” points out the possibility of superseding gas or other incandescent tubstances as means of illumination at night. Dr. Phipson points out that a whitewashed cottage exposed during tho day to a strong sunlight sometimes shines at night with a brilliant phosphorescent light; pure lime or a mixture of lime and nitrate of lime possessing the property in question. The substance used in preparing luminous clock faces is sulphide of calcium, sometimes known as Canton’s phosphorus, Canton having prepared it by heating a mixture of three parts of calcined oyster shells with one part of sulphur to an intense heat for an hour. It may also be formed by heating gypsum with charcoal. Tho most refrangible or actinic rays are most active in producing this phosphorescence, or fluorescence. Mr Woodbury, so far as wo know, is tho first to give this property a practical purpose in photography. Ho applies the sulphide of calcium in powder to tho imago formed by light on a surface possessing an elective degree of tackiness, and tho imago being so formed and submitted to the action of sunlight, or even a good artificial light, presents a luminous picture ia the dark. Used with judgment, such portraits may bo found very interesting, while, perhaps, nothing could be tcoro ghastly than the unexpected presentment of such a portrait of a deceased friend.