Physical developer is a silver-based aqueous reagent that reacts with the components of sebaceous sweat in latent fingerprints to form a silver-gray deposit. Physical developer is superior in sensitivity to many silver nitrate products presently in use. It can be used to develop latent prints on paper and other porous materials. Normally, physical developer is used on latent prints after they’ve been treated with ninhydrin. Just mix the solutions and immerse documents in the mixture. Rinse and wait for prints to develop. A technical information sheet and procedure recommendations are included with each set, which includes A and B solutions.