Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween ® 20 as an alternative to Triton™ X-100.

•Powder suspension performance varied between batches of Fisher iron oxide I/1100/53.•A greater number of particles <1μm was measured in the more effective powder batch.•Tween® 20 was shown to offer contingency if Triton™ X-100 becomes unavailable.•The effectiveness of some iron oxides may vary between surfactant systems.•A new Tween® 20/iron oxide nanopowder (Sigma Aldrich) formulation is demonstrated.