What is the test method for color fastness to soaping?

Soaping color fastness is one of the most common color fastness assessment items. Soaping color fastness refers to the degree of fading of colored fabrics after soaping under specified conditions, which includes two evaluation contents: original fading and white cloth staining. As-is fading refers to the fading of colored fabrics before and after soaping; white cloth staining refers to the situation that white cloth and colored fabrics are sewn and stacked together in a certain way, and after soaping, the white cloth is stained due to fading of colored fabrics.

The degree of fading or staining should be tested under the specified light source and graded on a standard gray card. The results are divided into 5 grades, with 5 being the best and 1 being the worst.