wet plate negative copper intensification

A Wet plate collodion image made over a transparent substratum can be seen as a positive image by reflection or negative by transmission. In order to be used as positive the density must be low. A collodion negative, on the contrary, needs high densities to be effectively printed, especially through old photographic techniques, like salted paper or albumen print. This is why a process of intensification must be performed after development. The two main process are iodine and copper intensification. Iodine is a bit tricky, but allows a better control of the result. Copper procedure is easier and quick, and in old times has been for these reason preferred for itinerant collodion. Here a tutorial for this technique.