From the manufacturer:
Safe for most fabrics and embroidery flosses. “Most”, because it wasn’t possible to test on every fabric and floss on the planet, so test your fabric and floss choices, just to be safe, especially reds. There are so many variables in the process of fabric dyeing so please test. To use, spray area or use Blue Line Eraser Applicator. STRONGLY RECOMMENDED: Before using detergent to wash, rinse project in plain tepid water. Some detergents may react to residual ink and leave brown lines on some fabrics if not rinsed in plain water before laundering.