I sent Pilot an email asking is the Frixion pens were archival. This was the reply:
[h=4]All Pilot Gel Ink Pens, Ball Point Pens and Markers are Acid-free and Archival safe, meaning their inks do not contain any acidic chemicals that may speed the deterioration process of photos and documents. Acid-free / Archival safe inks contain pH levels of 7.0 or greater meaning they’re non-acidic.[/h]