Fingerprint detection. Forensic scientist testing a latex glove for fingerprints using RTX, the vapour of ruthenium tetroxide. This reacts with the fats in fingerprints, a reaction that forms a dark colour, enabling previously invisible prints to be seen. RTX is typically used for finding prints on latex and similar materials. The face mask she is wearing protects her from the toxic RTX fumes. Fingerprints are unique to every individual and can thus be used to determine who has worn or handled the glove.