I'm getting some work done on my house and the guy doing the work wanted to test for lead paint. He scratched an area on a window sill, rubbed it with the spongy tip of a swab, and immediately declared it lead free cause it didn't change to the color of red. However, I just walked into the room three hours later and see the two spots he tested are both red. So what should I think of that?

I presume his test kit is designed to give an immediate result and, hours later, might be showing residue of lead from decades ago. Or perhaps just the breakdown of the chemicals in the test. I don't know.

EDIT: From looking around, one "instant" lead check swabber recommended by the EPA said theirs gives results in 30 seconds. We weren't in the room long but it was longer than 30 seconds.

enter image description here

  • Are the spots a deep red (indicative of lead) or more-so rust orange (possibly staining from the test liquid)? Could you take a picture? Commented Aug 22, 2017 at 18:17
  • I would want to know what the kit said. Many chemicals once activated breakdown. If your home is older than 70's you can almost guarentee that there is lead based paint on the lower layers of paint.
    – Ed Beal
    Commented Aug 22, 2017 at 18:40
  • It's not a deep red like the comment button over there --> or the answer button below. Maybe 50% lighter than that. I'll put a picture up if that might help.
    – Rob
    Commented Aug 22, 2017 at 18:44
  • You may have several layers of paint on this sill, and the test finally permeated down to the older lead based paint layer. The only reliable way of immediately testing is a portable X ray machine.
    – ajeh
    Commented Aug 22, 2017 at 19:38
  • No, the only reliable way of immediately testing is to actually follow the instructions in the test kit... instead of disregarding them and freestyling it and then wondering why your result is ambiguous. I would agree if you need to test a lower layer, it'd work better to wet-sand down to it first. Commented Mar 31, 2020 at 21:34

3 Answers 3


Do you have any kit materials left? Swab a surface where you are absolutely certain there can be no lead and check it three hours later.

Test on something portable, so you can view it right next to the windowsill.

  • No, I have no leftovers.
    – Rob
    Commented Aug 22, 2017 at 20:01

I'm Lead Certified. That's orange, not red. That's just testing positive for Penetrol, or some derision thereof. It makes paint flow better. Not a danger to you or your windowsill lickers.

  • What about the timing? Would the color change outside of few mins and into 24 hours count as test result?
    – Amir
    Commented Apr 30, 2023 at 15:45

When in doubt about a lead test that someone else has done, you can always buy your own test kit relatively cheaply (the last kit I picked up had two test swaps for about $7).

Then, you can read the directions and execute the test yourself. This should give you confidence about what the test results mean. I would recommend using one of the testers on something that you know for a fact to contain lead so that you can see the expected color as some of the kits will leave an orange residue which could otherwise leave you wondering if the areas you happen to test are all lead-free.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.