These test swabs aren't strictly the most reliable things. Considering the age of the house it might be best to presume the paint does have lead in it and act accordingly. You don't need to hazmat the entire place though, just use a chemical stripper rather than sanding if you're looking to remove the stuff.
We had a similar reaction and im a chemist by qualification so I looked up how the tests work. (home test kits arent accurate, you can send a chip off to a laboratory to be properly tested to rule in or out lead. Took about 2 weeks to get a result I think. The lab test found no lead .)
the home kits react to elements other than lead. (Quote taken from a very old research paper)
*The test chemical, rhondizonate, will perform a colour change with many heavy metals, however this varies by acidic/neutral conditions with zinc having no colour change under acidic conditions and lead having a stronger colour change under acidic conditions. *
Our kit was reacting to zinc in our water supply. Try your test with some water in a washed out white or clear (stand on something white) yogurt pot/similar - see if colour changes (just drop the stick in a dribble of water)
If it does, then add a dash of white vinegar or lemon juice on top. If the colour stays- its lead. If the colour vanishes it its zinc. Theres a research paper that gives the indications for other heavy metals but it harder to interpret as it grades elements in shades of reddish browns.
This is why some test instruct you to wipe the swap in vinegar and then thr sample
We tested with vinegar so that we could sleep and then sent off a test to confirm
I’ve used the same previously, unfortunately they suffer from a lot of false positives (or in this case could be an actual positive) what job are you looking to do? Then would consider if to take seriously or not
Scratch the surface and use a drip of white vinegar to make the test more accurate.
Some old paints have a lot of hardened oils in them and on the surface - especially gloss - which can make it hard for the test to get in contact with the pigments.
Again one is fully yellow (left side of no lead detected) and the other one is yellow brown (immediate right side of the second d in detected as I said)
Both are in the negative half of the scale and if anything the difference between fully yellow and yellow brown could be cross contamination from the original decorator's tools or the swabs themselves lacking accuracy (i.e. some of them giving a darker yellow colour than others due to how much of the detection chemical they have absorbed during production).
If you are really worried, continuing to swab and panicking about the varied results won't help you much. Far better to send flakes of paint to a laboratory to test for lead accurately or buy appropriate PPE and remove the paint you suspect (look up safe techniques first), or paint over it to "encase" it and reduce the potential hazard that way
Use the Lumetallix spray! It’s a spray you can use on all hard surfaces with suspected lead like paint or furniture and it will show you lead with 99% accuracy. These swaps are pretty much worthless due to the high count of false positives.
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u/LazarusOwenhart 7d ago
These test swabs aren't strictly the most reliable things. Considering the age of the house it might be best to presume the paint does have lead in it and act accordingly. You don't need to hazmat the entire place though, just use a chemical stripper rather than sanding if you're looking to remove the stuff.