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The amount should only be about the size of a grain of rice. While you want the primer to cover your eyelid completely, too much primer can completely backfire. It can cause your makeup to pill, clump, appear chalky or shiny. Too little, and your eye makeup won't stay. This amount of primer should be enough for both eyes. It's always better to start with less product and build layers if you need to instead of starting with too much and trying to wipe it off. Remember: less is more when it comes to primer. It should take about 20 seconds for the primer to absorb and dry. You can then apply your eye makeup as you normally would. Your eyelid should feel like a flat canvas and your shadow should go on smoothly. If it appears cakey or clumpy, you used too much primer and should use a little less next application. Try using the primer on your eyebrows to keep brow powder in place, too.
Dab a small amount of primer on the back of your hand. Allow the primer to dry before completing your eye makeup.