The principle behind the test is that Phadebas®, consisting of starch microspheres with a blue dye cross-linked to the starch, are immobilised on filter paper sheets. In the presence of amylase the starch is digested, releasing the water soluble dye, which diffuses through the pores of the filter paper. The resulting blue colour is visually observed on the non-reagent side of the Phadebas® paper. The Press test is performed when it is necessary to localise an amylase positive area on an item. If a very strong reaction is obtained with the Press test and there is no other obvious contaminating material, this is interpreted as an indication of saliva. The following link illustrates the methodology and simplicity with an Overview of Phadebas Forensic Press Test. For detailed instructions; please follow Phadebas Forensic Press Test Instructions.