If you’ve ever stained a white shirt or wanted to try custom designs on fabric, you’ve probably run into the humble bleach pen. These handy tools let you target spills, tackle old mildew in grout, or doodle on dark T-shirts for custom patterns. Store-bought versions work well, but making a DIY bleach pen can save money, give you more control over strength, and opens the door for creative projects. Grab your kitchen gear—let’s get started.