The colour of dissolved iodine has been linked to the formation of iodine-solvent complexes (for red/yellow) or the presence of 'unsolvated' diatomic iodine (violet). These observations lend weight to the assertion that the spray's effectiveness relies upon iodine's poor interaction with the carrier solvent to promote concentration and retention within a fingermark. Ultimately, an optimal ratio of 5:1 HFE-7100 to heptane was found to solubilise sufficient iodine to provide strong fingermark development (Fig. , right), and that blend was found to be stable for at least four hours once made. Like iodine, the α-naphthoflavone stock solution could not be created from neat HFE-7100 due to poor solubility. A range of blends were assessed, including green solvents such as ethyl lactate and cyclopentyl methyl ether; known additives acetic acid and dichloromethane; and common laboratory solvents including acetone, ethanol, methanol, and dimethyl sulfoxide. The greatest challenge in developing the α-naphthoflavone stock solution was ensuring compatibility with the iodine stock, as an incompatible mixture would result in rapid reaction of iodine and αnaphthoflavone in solution, or precipitation of one or both reagents. Either scenario resulted in an all-in-one mixture that produced poor fingermark visualisation. As seen in other all-in-one blends, use of dichloromethane to dissolve α-naphthoflavone produced the best outcome upon later mixing with the iodine stock solution. After standing for 5-15 minutes and filtering, the resultant all-in-one spray remained stable for up to 4 hours and produced good visualisation when applied to fresh natural fingermarks on gyprock, tile, and plastic (Fig. ). As with other reports, it was essential to completely dissolve each chemical component in the more-solubilising solvent before diluting with carrier solvent. Not doing so would typically prevent complete dissolution of the components, particularly as the high volatility of HFE-7100 impeded the use of vigorous heating to assist with this. The intensity of fingermark development appeared dependent on the total amount of free iodine stabilised within the solution, iodine being the reagent with the greatest solubility challenges in terms of dissolution and retention. The need to inhibit the reaction kinetics of iodine and α-naphthoflavone to limit in situ reaction prior to uptake by the fingermark further complicates this situation. To compare the effectiveness of the blended HFE-7100 all-in-one spray against the established AK-225 spray, a split depletion series was placed across two halves of a ceramic tile, with each half then being subjected to either the HFE-7100 or AK-225 treatment. It was found that the HFE-7100 spray gave enhanced visualisation of fingermark residues relative to the AK-225 spray in that it was able to visualise marks further down the depletion series (Fig. ). Fig. . Comparison of a depletion series on tile treated with HFE-7100 blend (left) and AK-225 blend (right) showing enhanced visualisation with the HFE-7100 all-in-one blend. Note: