1, right), probably due to the residue providing stabilising interactions in the form of ionic and halogen bonding that are lacking in solution. Many common laboratory solvents were assessed, but only aliphatic hydrocarbon solvents (e.g. pentane, hexane, cyclohexane) were found to direct iodine into the fingermarks after application, cementing the choice of heptane as the additive when creating the HFE-7100 blend. Inclusion of heptane in the spray imparts a flammability hazard; however, blending similar flammable solvents is not uncommon in analogous Category A HFE-7100 developers (e.g. DFO), or other recommended HFE-7100 developers (e.g. IND). During the assessment of different solvents, the colour of the iodine solution offered some indication of its suitability for use as a fingermark developer, with violet iodine solutions being suitable (e.g. Fig. , left), whereas yellow, red or brown solutions imparted minimal development.