Soldering terminology

Test paper described by Joint Industrie Standard IPC J-STD-004B (Testmethode descibed in IPC-TM-650, Method 2.3.33). Immersed in flushing liquid and then extracted, the discoloration of the red-brown Ag2CrO4 test paper indicates the presence of soldering residues such as halogens chlorine and bromine. The size of the stained area is proportional to the concentration of chlorine and bromine. The following chemical reaction occurs:

Ag2CrO4+2 Cl-    2 AgCl white↓ +CrO4+2 Br-     2 AgBr yellow +CrO4