With the goal of creating an all-in-one HFE-7100 spray that could act as a stopgap should HCFC and HFC-based solvents be phased-out or phased-down, inspiration was drawn from the existing and past developer formulations (Table ). It was quickly recognised that inhibiting formation of the iodine-naphthoflavone adduct in HFE-7100 constituted a core challenge, with instantaneous or continual precipitation resulting if the blending solvents were insufficiently solubilising. The low dielectric constant of heptane and HFE solvents are useful in this regard, inhibiting dissociation of neutral iodine into reactive charged species in solution, resulting in negligible reaction with α-naphthoflavone prior to encountering fingermark residue.