GB/T 30789.2-2014 "Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and size of defects, and of intensity of uniform changes in appearance — Part 2: Assessment of degree of blistering" is part of a series of standards for evaluating the aging of paint and varnish coatings. It is equivalent to the international standard and specifies the method for assessing the degree of blistering of coatings. The core principle involves grading based on the number (density) and size of blisters, using standard rating charts as a reference, and combining visual observation to quantitatively evaluate blistering defects in coatings after aging tests. The assessment process requires the use of a standard light box to ensure consistent observation conditions, and a magnifying glass may be used to assist in identifying small blisters. This provides a unified and standardized technical basis for evaluating the aging performance of coatings, ensuring comparability of results across different testing scenarios.