There are only two situations for which bleaching is necessary:1/ if you want to have platinum hair, because you have to oxidize as much as possible to remove all the pigments present in the fiber; 2/ if you want to lighten or get rid of oxidation coloring (see Coloring in questions #2). In other cases, you can do without it.
It depends. "In the case of an oxidation coloring where we mix a tube of coloring and an oxidant, a chemical reaction takes place (the one that creates the final color) and the mixture must be applied immediately", explains David Merveille, Schwarzkopf consultant hairdresser. If we keep it for next time, the colo will dry out, but above all, it will lose its coloring power (without however being dangerous). On the other hand, if you have not mixed all the products, you can keep what remains of the dye and oxidant, provided you close the containers well. It's useful if you just want to camouflage white hair:mix a dose of oxidant for a dose of dye, and apply the mixture with a toothbrush.
Another case where the formula can be kept:when it is offered in a double aerosol that isolates the colorant and the oxidant, such as the Preference Mousse Absolue from L’Oréal Paris. There, the mixture is made only by pressure.
Thanks to Frédéric Mennetrier, colorist at Atelier Blanc and L'Oréal Professionnel expert, Rodolphe Lombard, colorist at the Salon Couleurs par Rodolphe and David Merveille, Schwarzkopf consultant hairdresser.
