Abstract: The distribution of copper and silver within the final image obtained by copper phys-ical development and the reduction of Au³⁺ by gelatin in non-image area were studied.Itwas indicated that the copper content increases with the increase of depth,whereas the sil-ver content decreases with the increase of depth,The shift of the bind energy of Ag3d to alow value shows that the silver in the interior of the image is in a mixed state of monoatomsand polyatoms,but the silver at the image surface is exclusively in a monoatomic state.Ifthe time of copper physical development is long enough,copper will completely cover silver.From then on the copper physical development continues because of the autocatalysis ofnewly formed copper.It was shown that much more chloroauric acid was absorbed in thenon-image area and hence the deposition speed of copper was much faster than that in theimage area.Gelatin can reduce Au³⁺.The reduction process might be divided into twosteps.The first step, which is fast at the room temperature,is the formation of Au⁺,andthe second step,which is relatively slow,is the formation of gold.Au⁺ and gold mightact as catalytic nuclei during the copper physical development depositing copper in thenon-image area.

Key words: copper Physical development, electron diffraction, X-ray photoelectronspectroscopy, reduction of Au³⁺