Photoetching failing step 3

Next step is to try and get '"a photo sensitive brass sheet'". So then. I bought several 0.2mm small sheets of brass at a local RC shop and proceeded to spray some photosensitive resin on the plates in a dark place -for the light not to interfer when the stuff is drying. Big problem: any grain of dust falling on the still wet product led the liquid to coagulate near the grain of dust because of the capilarity, which means I had a lot of trouble to get an even surface.