[MUSIC] [MUSIC] Now, sometimes, fingerprints are visible. Juan Vucetich, for instance, the fingerprint that convicted Francesca Rojas was a visible fingerprint because it was in blood. But many fingerprints are not visible to the naked eye, and these are referred to as latent fingerprints. And latent fingerprints require some artificial means to make them visible, and typically they require treatment with a chemical for chemical visualization. So in order to understand chemical visualisation, we need to remember what fingerprints are made of - metal salts, amino acids and proteins, fats, and water, but of course, the water is not going to last very long because that's going to evaporate. The simplest way to visualize fingerprints is to use a dusting powder, and this is not strictly a chemical method, it's simply the physical adhesion of the powder to the fingerprint. There are various dusting powders available, but the general idea is that you choose a dusting powder that will contrast with the background. So, if you're looking for fingerprints on a white surface, then you can use a black powder like carbon black. If you're looking for fingerprints on a dark surface, then you can use a light powder like aluminium. The powder can then be lifted off onto tape and photographed and preserved. There are also various chemical reagents available. For instance, the object can be sprayed with ninhydrin, which reacts with the amino acids present and makes the latent fingerprint visual. Other chemicals are like iodine or silver nitrate. There are also physics-based methods, for instance using a laser to get laser fluorescence, which can be done alone or in combination with a dye. One of the most effective methods is the so-called fuming cyanoacrylate method, and that sounds very technological and sophisticated until you realize that cyanoacrylate is just super glue. And this is a technique that was discovered accidentally by two Japanese police officers, and they were using super glue to fix some objects down when they realised that the super glue was causing fingerprints to show up. The mechanism is not clear, something in the fingerprint, possibly the amino groups of the amino acids, is inducing polymerisation of the cyanoacrylate molecules in the super glue vapour. But what is happening is the super glue is depositing on the fingerprinting, making it visible. So nowadays, it's not done by accident; there are specific devices. Fume chambers - some of these can be quite small for small objects, but you can get commercial super glue fuming chambers big enough for rifles. You can fume an entire car in order to find fingerprints. So it's proved to be a very useful method. [BLANK_AUDIO]