If you live in the US, Nearly Everything.
Lead detection, professionally speaking is relegated almost exclusively to XRF.
EPA Lead Regulations Define XRF or X-Ray Fluorescence
as a valid method to detect lead using X Rays in homes, provided the manufacturers provide a PCS, or performance characteristic sheet with the instrument. the PCS sheet is basically just a marshaling of the results of the instrument on different substrates, wood, concrete or drywall for example. These used to be more important for operators when the XRF instruments were less sophisticated.
They basically work like this, the purple box is either an X-ray tube (modern) or a sample of Radioactive material (legacy) that emits X-Rays onto the sample.
The sample reflects the X-Rays, which are really just a really short wave form of light back at the detector (and in all directions) in the following way. This is known as characteristic radiation, the "color" of the characteristic radiation depends on the substances the rays hit.
Credit for this animation given to Prof. Jacopo Bertolotti who is an Associated Professor of Physics at University of Exeter
@j_bertolotti on X/Twitter.com
Some of this radiation makes it way back into the device and hits a sensor, recently the sensors have become much more sophisticated. They read the "color" of reflected light in the following way.
Made in 2018 which I purchased off ebay for 32 thousand dollars, it uses an X-Ray Tube X-Ray source and a detector chip as described above.
This is a really sophisticated piece of technology, an engineering wonder.A -1000 volt biased gold plated chip with a Silicon doped with Lithium component sandwiched in between two semiconducting Silicon components leading the charge to the computer out of the gold plated other side.
No wonder its so expensive.
While costing me 32k on Ebay lacks a PCS sheet so it cannot legally be used to clear peoples homes for lead in a way that abides by the EPA rules and is only for "industrial paint". With this being said it works just fine on any paint as described by the readings I get when I scan the included calibration paper with samples of known quantities of lead paint.
With this being said its an incredibly versatile piece of equipment, it can detect metals in consumer goods, soil and metal.
Insofar as detecting lead is concerned this is a wonderful tool, it detects it quickly, accurately and without leaving a trace.
The only drawbacks are the X-rays, the cost, complexity and the limited fidelity of the readings produced.
The detection window on my unit is less than 1 square centimeter. Giving a tiny glimpse of the surface.
Also this does nothing to determine if the paint is on the surface or underlies other, non-lead paint, other than giving a lower reading if this is the case.
And because of the cost it must be deployed in an expensive manor, costing upwards of 300$ for a home inspection.
While the technology advanced it has not offered a Deus ex machina type of solution to lead detecting in the home.
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