A borax bead made with a trace of a salt is yellow-brown when hot and yellow when cold in the oxidising flame, and bottle green in the reducing flame. The metal ion present is

Iron gives $\mathrm{Fe}{}_2(\mathrm{BO}{}_2){}_6$ (yellow or brown) in the oxidising flame, and is reduced to the bottle-green $\mathrm{Fe}(\mathrm{BO}{}_2){}_2$ in the reducing flame. Nickel gives a brown bead then a grey one, manganese gives an amethyst bead that turns colourless, and cobalt gives a blue bead in both flames.