Which test involves removing a small patch of coating to assess soluble salt levels?

The Bresle Patch test is specifically designed for assessing soluble salt levels on surfaces prior to coating application. This method involves placing a patch on the surface, which is sealed to create a confined area. A solvent, typically water, is then introduced into this area, allowing the soluble salts present on the surface to dissolve into the liquid. The solution is collected and analyzed, providing a quantitative measurement of the soluble salts. This is critical because high levels of soluble salts can adversely affect coating adhesion and performance.

In contrast, the other methods mentioned serve different purposes. The potassium ferricyanide test is used to detect the presence of iron ions in coatings, while the alligatoring test assesses the appearance and condition of the coating surface for cracking patterns associated with aging. Visual inspection is a general method for observing surface conditions, but it does not provide the specific quantitative assessment of soluble salts that the Bresle Patch test does. The uniqueness of the Bresle Patch method lies in its ability to effectively gauge contamination by soluble salts, ensuring proper surface preparation for effective coating adhesion.