Notice the difference in gloss between the highlight and shadow areas. The carbon process involves making an exposure through a negative onto a thin tissue containing pigments and dichromate gelatin. This gelatin becomes insoluble in water to a degree proportional to the light passed through the image. During the transference of the pigmented gelatin to a transfer paper the gelatin is washed away, leaving a gelatin relief image that is later transferred to the final support. This relief causes the differences in gloss between highlight and shadow areas.