Peckish

I respectfully disagree. Who told you this? When I found my first Frixion pen 4 or 5 years ago, I did a LOT of research about them. I searched the internet and contacted the manufacturer. They were never designed for fabric. The manufacturer might be marketing them as such NOW, since there's been such chatter about them, but that still doesn't mean they were originally engineered for this purpose and contain acid-free ink.

But, to each her own. If you want to use them in your quilt, by all means do so. As I said, I still prefer to use products that I KNOW are safe.