The destructive nature of the test and the turnaround time has discouraged many from taking the lab approach. Expense has been another turn-off. However, prices are dropping. With prices going down, it's becoming more and more practical, too. They work on the principle that a chemical impregnating a swab will change color in the presence of lead.
Painters have their choice of two different chemical tests.
One contains sodium sulfide, a testing chemical approved for lead detection in Massachusetts. The sulfide component attaches to any lead in the paint film, making the swab turn a dark color. That means a lead-free paint film with traces of copper or nickel could produce a color change. That's called a false positive. And you may not be able to tell whether the swab has darkened if the paint is dark itself.