The test at Freckled Whimsey said something I couldn't believe until I checked it myself. The Pigma Micron company website says that the pens are NOT to be washed! Here's the quote - Fabric design* note - the inks on fabrics are for "decorative purposes only" - meaning do not launder.
Here's the link, it's near the bottom of the page.
http://sakuraofamerica.com/pen-archival
Tate