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Going light once you've dyed your hair brown is possible, but it won't be as easy. Once you've put artificial, permanent color on your hair, you can no longer simply lighten it using hair color alone. What you need now is a two-step decolorizing process that wipes the slate clean and lets you put on the color you want. It's an extra step, and a little harder on your hair, but if your dying to be a blond bombshell then it's the only way to go.
As with any successful journey you need a starting point and a destination. Your first step in the quest for blond hair is to figure out exactly what level of blond you really want. Look at some color swatches. You can find them wherever hair color is sold. Choose the blond shade that matches your style. Note the level number associated with that color. It will likely be eight, nine or 10. Now match your current light brown hair with the hair swatches and note the level number of that hair color too. The difference between the number for your current color and the number for the color you want will determine the strength of developer you'll need to apply to your hair.
Products Used to Lighten
One of the biggest rules in coloring hair is that color cannot lift color. Your current light brown hair is now immune to a simple bottle of dye. You must bring in the hair bleach muscle to get the job done. You'll also need the appropriate strength of developer to mix with the bleach to provide enough lifting power. If you are lightening your hair two levels, say from a level six to a level eight blond, you'll need 20-volume developer. For three levels of lift, you'll need the brute strength of 30-volume developer. The bleach is mixed with the developer and applied to the hair until it lifts out both the artificial and natural pigments until it reaches the appropriate color.
When the bleach is on your hair there's going to be a certain level, or color, you're trying to reach. This color won't be the end result; you'll achieve the final color during the toning process. But this goal color will be your indicator that you've removed enough of the artificial color and underlying natural pigment to get your hair to the blond color you want. If you are aiming for a level eight blond you'll want to bleach the hair until it is a medium-yellow color, without any hues of orange in it. For levels nine and 10 you'll be looking for a pale yellow shade instead. Keep a constant eye on your hair when it's bleaching and rinse the moment it gets to your target yellow shade.
Toning is the process of removing any remaining, unwanted underlying pigment and creating a softer, more neutral shade. Semi-permanent hair colors make the best toners around. Because the hair has been previously lightened, these colors will actually tone the hair on a permanent basis, so you don't have to worry about the final color fading out in a few weeks. For a level eight blond, mix a level eight semi-permanent hair color with 10-volume peroxide and a cap full of violet toner. The violet toner removes the excessive yellow pigment and leaves you with a beautiful blond shade of hair. For level nine or 10 blond, mix the corresponding semi-permanent shade in the same level, along with 10-volume peroxide and a cap full of violet toner. The toner is applied all throughout the hair and left on for 20 minutes.