Go to the testing tab on the site, it is explained in writing and the video. Also, look at instructions from kit.
Do not use the rapid test method on bare metal or bare wood.
This could happen with items other than lead. I just address the yellow to black color and stress that the customer makes sure that the item being tested does not bleed.
In the 8 & 24 pack test kits there is no shelf life. The 100 test pack shelf life is 2 years.
Any clear white vinegar
That answer depends on what you are testing. The U.S. Consumer Product Safety Commission says that on August 14, 2011, manufacturers, importers, retailers and distributors of children’s products must comply with the new 100 ppm federal limit for total lead content. The EPA recommends a maximum level of 10 ppb in drinking water.