Kronstadt -failing the photoetched parts

When those 3 minutes are over, you go back to the cellar and put the brass plate in a mix of 1/8 water and photo revelant stuff -I don't know the word, but it's the product the photographers use to develop the pictures. After 3 or 4 minutes a picture starts to show, and here you can see the catastrophe, because the '"holes'" in the pic are because of the dust grains that attracted the photo resistant product..