Coffee Grounds for Hair Coloring
A: You can indeed make brown hair dark with coffee grounds. You can make almost any hair color darker with coffee grounds. The color change is not likely to be very lasting, given that it depends on the hair being porous enough to allow the water-based transfer of tinting into the hair.
However, since the coffee grounds are not designed to be permanent color, you may find you have trouble with things like transfer stains on clothing and upholstery fabrics, as well as color bleeding in hot, moist climates or if you perspire heavily.
Coffee grounds can also present a problem on hair by imparting an irregular color application. You may find better results with doing a cool rinse of very strong coffee (possibly including the grounds) in order to provide a more even coverage.
And while you can use the process on any lighter color of hair, it does work best when used to deepen a color that is already in the same family.
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See also:
Color your hair with fruits and berries
Natural ways to achieve highlights
Natural hair color products
How to dye your hair with henna