There are many ways that you could perform a test for small amounts of lead in lipstick (or any other cosmetic). The most accurate, but most expensive way would be to do an x-ray fluorescence measurement. In this technique you would put the sample in a machine which would bombard the material with x-rays (a really high energy light), a detector would then be used to measure the wavelengths of the light that were released from the specimen after the x-rays were absorbed. By comparing these wavelengths to known standards you can get an elemental map of all the elements the product contains (including lead). As an alternative, since you probably do not have access to an EDX machine, they sell lead test strips that you can dip into a solution and measure lead content. These test strips are cheap, so what you could do is dissolve some lipstick in water by heating it on the stove and then dip a test strip into the solution to test for lead. This will be less accurate, and you may have trouble dissolving the lipstick, but you could try dissolving it in different solvents (like vegtable oil, rubbing alcohol, vinegar, or hydrogen peroxide) and then dip the test stick in. You will need a sensitive test stick for this, but kits with sensitivity of (15 parts per billion) are available for about $23 online.