How to Use a 40% Developer With Toner

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When you color your hair, you need to use both toner and developer. Boxed hair-dye kits already contain developer, typically in the form of hydrogen peroxide, to open your hair which allows the color to penetrate. The volume of the developer defines how much it oxidizes the hair, with a stronger volume necessary for darker hair colors or to achieve lighter shades. If you don't properly mix toner and developer, you may not achieve the desired results with your hair color or end up with a formula that is too runny.

Purchase 40 percent developer and the color of toner you want to use to dye your hair.

Put latex gloves on to protect your hands from color staining.

Pour equal parts of developer and toner into a plastic hair-dye mixing bottle. Place your finger over the tip and shake the bottle vigorously until the toner and developer are completely mixed.

Apply the mixture all over your hair, being sure not to miss any sections or spots. Have a friend check to ensure you have covered all areas of your natural color.

Rinse the mixture out completely after the time allotted on the bottle. The length of time the mixture needs to sit in your hair varies depending on the shade you're trying to achieve and your natural hair color.