Some of the laser dyes are rhodamine (orange, 540–680 nm), fluorescein (green, 530–560 nm), coumarin (blue 490–620 nm), stilbene (violet 410–480 nm), umbelliferone (blue, 450–470 nm), tetracene, malachite green, and others. While some dyes are actually used in food coloring, most dyes are very toxic, and often carcinogenic. Many dyes, such as rhodamine 6G, (in its chloride form), can be very corrosive to all metals except stainless steel. Although dyes have very broad fluorescence spectra, the dye's absorption and emission will tend to center on a certain wavelength and taper off to each side, forming a tunability curve, with the absorption center being of a shorter wavelength than the emission center. Rhodamine 6G, for example, has its highest output around 590 nm, and the conversion efficiency lowers as the laser is tuned to either side of this wavelength.