Physical developer - In order to test the reliability of a prepared PD workingsolution, two procedures were proposed: (a) printed standardized test strips using amodified inkjet printer (228), and (b) EDTA spot tests on Whatman #2 filter paper(229). The pattern developed by Kupferschmid et al. contains geometric shapesmade of ascorbic acid and oleic acid aqueous solutions (used as inks by the printer).The correlation between the number of detected shapes on the test strip and thequality of fingermark development was shown to be high. The EDTA spot testprocedure represents an inexpensive, reliable, stable, and rapid alternative to aprinted pattern as well as to gold chloride spot tests on filter paper. The shelf-life ofthe last PD formulation (in which Synperonic N has been replaced by Tween 20) hasbeen thoroughly studied (230). As a result, it has been shown that the shelf-life of thePD working solution was of 10-15 days for the Synperonic N formulation, but rises upto 2 1/2 months when using Tween 20. The robustness of the PD formulation wastested by comparing the efficiency of different working solutions, among whichvoluntary alterations and modifications were introduced (231). It has been shown that