How do meth lab test kits detect the presence of a meth lab?
Simple self-made or commercially available tests use the Marquis reagent, which is a mixture of sulfuric acid and formaldehyde. For example, Marquis reagent can be prepared by adding 100 ml of concentrated sulfuric acid to 5 ml of a saturated aqueous solution of formaldehyde (40 % formaldehyde by volume or 37 % by mass).[reference]



The Marquis reagent reacts with many alkaloid drugs to form a variety of colours. Methamphetamine creates an orange dye (deep reddish orange to dark reddish brown).