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You're a unique kind of lady, so those one-formula-fits-all boxed colors just aren't going to cut it. Blending the developer into your own color creation is actually a pretty straightforward task. The key to doing it right is to have all your necessary tools and ingredients ready before you start mixing so you don't lose track which step you're on and ruin your beautiful concoction.
Measure out the amount of semi-permanent color you'll need into your color bottle or bowl. For a typical application you'll probably need to use the whole bottle or tube of color or a mixture of two colors to equal said amount.
Add the recommended amount of 10-volume developer. In most cases, the ratio will either be equal parts of color and developer or two parts color to one part developer. Check out your product's directions so you can be sure to get it right.
Mix the color and developer thoroughly. If you're using a color bottle, screw the lid on tightly, place one finger over the open nozzle end and shake it up, baby, until the color and developer are totally incorporated and the mixture is one, consistent color. If you're going the bowl and brush route, you'll use your color brush to mix the two together until all the lumps are removed and the mixture is consistent in texture and color.
Your hair color is now properly mixed with your developer and you're ready to apply the color to the hair. Have fun!
Always use a 10-volume developer with a semi-permanent color to keep the color "deposit-only" and temporary. Using a higher volume of developer, like 20 or 30-volume, will turn your semi-permanent color permanent.
Once the color and developer are mixed, a chemical reaction begins to occur. You now have only 30 minutes of potency in that color before the prolonged exposure to the air renders it useless. That means you've got to work fast and apply that color ASAP.