This is most commonly performed using lasers, which break down the ink particles in the tattoo. The broken-down ink is then absorbed by the body in a process that mimics the fading that time or sun exposure would naturally create. All tattoo pigments have specific light absorption spectra. A tattoo laser must be capable of emitting adequate energy within the given absorption spectrum of the pigment to provide an effective treatment. Certain tattoo pigments, such as yellows, greens and fluorescent inks are more challenging to treat than darker blacks and blues, because they have absorption spectra that fall outside or on the edge of the emission spectra available in the tattoo removal laser. Recent pastel coloured inks contain high concentrations of titanium dioxide, which is highly reflective. These inks are difficult to remove since they reflect a significant amount of the incident light energy out of the skin. Complete laser tattoo removal requires numerous treatment sessions, typically spaced at least seven weeks apart.