How does one test for lead in dry paint?
This site is not specialized and reserved to professional chemists. On the contrary. A lot of teenagers are using it every day.
Now if you want to identify lead in a dry paint, you may burn it in the flame of a Bunsen burner, and save the ashes. They contain a mixture $\ce{Pb + PbO + Pb3O4}$. Then dissolve the ashes in nitric acid (concentrated $\ce{HNO3}$ diluted with its own volume of water). Filtrate the insoluble part. Dilute the filtrate still more, by adding an equal volume of water. This gives you a lead nitrate solution, with which you carry out the following tests. Add some $\pu{1 M}$ $\ce{HCl}$ to a part of the obtained solution : it should produce a white precipitate of $\ce{PbCl2}$, if the solution contains some lead ions. Or add some $\ce{KI}$ solution : You would obtain a yellow precipitate of $\ce{PbI2}$, if the solution contains lead. The reactions are :
$$\ce{Pb(NO3)2 + 2 HCl -&gt; PbCl2(s) + 2 HNO3}$$
$$\ce{Pb(NO3)2 + 2 KI -&gt; PbI2(s) + 2 KNO3}$$
A further proof is obtained by heating the solution containing the yellow deposit of $\ce{PbI2}$, because this substance gets redissolved at $\pu{100°C}$. And after slow cooling, $\ce{PbI2}$ will precipitate back and it looks like wonderful golden plates, floating in the liquid. It is amazing. If these precipitate do not occur, there is no lead in your paint.