AUTOTYPE, one of the names given to a peculiar kind of photographic print. Gels, tine, to which hichromate of potash has been added, has the property of being, like paper, treated with certain salts of silver, sensitive to light, but in a different way. Light renders the bichromated gelatine insoluble, so that by the use of an ordinary pbpto graphic negative, we can produce a picture on the gelatine by exposure to light, as in the ordinary photographic printing process (see PuoToartArav). The picture so obtained is developed by removing with hot water those portions of the gelatine which have not been acted upon. Two groups of processes are founded on this property of bichromated gelatine. In the one, the gelatine is used for every copy of the picture; while in the other, it is only used to produce one picture, which is then made by various devices to serve as a printing matrix for throwing off, by mechanical means, many impressions.
What is called carbon-printing comes into the first group, and an autotype is one kind of a carbon print. It is produced by simply mnising carbon or other pigment with bichro mated gelatine, coating a sheet of paper with the mixture, and then exposing it to light under a negative as above described. When no pigment is used, the picture is merely in relief and depression, but the addition of carbon gives it ordinary light and shade, so as to resemble a print in ink. There are, however, some niceties in the manip ulation, which we have not room to detail..
In those processes where the gelatine picture serves only as a matrix, electrotypes, impressions in soft metal, or other kind of reverses, are made, from which impressions can be taken mechanically, in any kind of punting ink. Photo-galvanography and the Woodburytype belong to this group.