INTAGLIO PlIOTO-ENGRAVING. This is known by the general mime photogravure, a French term generally accepted in all languages. Hello gravure is a term IvIiich may be taken as the equivalent of photogravure, varying in meaning as does that inure general term: but at different times the name heliog,ravure has been given to special patented or secret processes. Photogra vure may have the appearance of pure line work, exactly as in manual line-engraving (Qv.), and it may have the appearance of tint or shade without line. nearly as in the case of mezzotint (q.v.). This form of the art has been carried to such perfection by some workmen, especially in France; that it is to be compared only to the finest and most artistica] hand work, having in addition to that artistic charm an accuracy of reproduction which the manual work cannot pretend to. Thns in the large books on paint ing and monographs of special painters issued during the last twenty years, and especially the more recent ones, such as De Bernete's reign quez, Yriarte's Mantegna, Lady Dilke's French, Painters of the Eighteenth Century, Armstrong's Gainnborough, Turner, and other volumes, and the splendid catalogues of public and private collec tions, photogravures alternate with half-tone prints and other prints from photo-engraving plates, but the photogravures are distinguishable at once by the fineness of their texture (pure line in the one ease and grain or texture in the oth in ivhieli no other process can approach them. In the ease of line photogravure the facsimile of a drawing or of a print from an engraved plate may be so perfect to be indistinguishable from the original except by the most minute examination of an expert. Thus in the published work of Amand-Durand of Paris, the facsimiles of fine prints from the plates of Darer, Rembrandt, Claude, Paul Potter, and other celebrated etchers and line engravers caused astonishment and doubt among collectors of prints when those fac similes first appeared about 1870. Here was an unquestioned original Rembrandt, not a copy, as any student of Rembrandt would know, and yet it was printed upon modern paper. In all these processes, however, hand work has to be called in to complete the plate; and it is a general truth that the most artistic workmen produce the most perfect photogravures. In the case of
Amand-Durand there was the peculiar advan tage that the director himself was a skilled en gayer before he undertook the photo-engraved process.
Gelatin treated with biehromate of potash is made insoluble under the action of light. In stead of gelatin seine other form of albumen may Ice used, or asphaltum, which is found to answer equally well and to be cheaper. In making a photogravure in line a photographic transparency, or positive, of the drawinolor print or picture or object which is to be reproduced is placed in contact with a copper plate coated with asphal turn or albumen mixed with a biehromate, and strong light is allowed to pass through the nega tive to the sensitized surface. Only those parts where the light passes through the negative with out interruption will be marked by complete insolubility of the gelatin; elsewhere the surface remains soft and capable of being dissolved away by washing. In this way the surface of the pre pared plate affected by light is turned into a relief copy of the original. The plate is then etched by an acid, perchloride of iron. which eats it away exactly as in the case of ordinary etch ing (see ETCHING). When it is a line plate which is being prepared no other important steps are necessary; but when the plate is to he a tint plate or gradation plate without line and pro ducing prints much like those taken from a mezzotint, it is usual to prepare the surface of the copper plate in the first place. by precipitating upon it a fine powder of resin or .1 resin and asphaltum in combination. This powdered sur face prevents the complete access of the mordant to the metal exactly as in the case of aquatint (q.v.). The granular surface so obtained may be either coarse or indefinitely minute. this depend ing upon the character of the subject to be re produced. In this way the reproductions of por traits by the greatest master of refined execution or landscapes of minute detail of most varied character may be reproduced with a perfectness of gradation equal to that of hand work in its highest perfection.