GB/T 30648.4-2015 "Paints and varnishes - Determination of resistance to liquids - Part 4: Spotting method" establishes a general method for determining the resistance of paint and varnish coatings to liquids using the spotting method. It is applicable for assessing the effects of liquid or paste test substances on coatings and substrates. The test requires the use of a pipette, a 50mL burette, and a 60mm diameter petri dish. After preparing and conditioning the test panels as specified, approximately 0.1mL of the test substance is applied using a pipette or burette. Changes in the test area are observed and evaluated according to agreed-upon criteria, providing a concise and practical operational standard for testing the liquid resistance of coatings.