Multi metal deposition (MMD) is a new latent fingerprint enhancement technique that is extremely effective on plastics, including drug wraps and explosives wrapping; it is also a potential reagent for the newly introduced polymer banknotes. Traditional Physical Developer involves deposition of a single metal (Ag) while MMD involves prior deposition of Au nanoparticles that act as nucleation sites for Ag deposition, resulting in enhanced visual contrast & greater recovery quality. MMD formulations include a non-ionic surfactant, whose presence is critical to stability and efficacy, but the means by which this is accomplished is not known: elucidating this is the key objective. We have recently demonstrated the capability of reflectivity to characterise the role of the surfactants on Ag. Here, we extend this capability to determine the structure and role of the surfactant (on Au) in MMD.