Acid free ink?

I'd never trust a fountain pen. You would have to just check the bottle of caligraphy ink to see if it says acid free. If not, contact the company that makes it and ask them. That's what I do when I am in doubt about any product before I use it in my scrapbook. They make lost of wonderful acid free pens, including caligraphy markers for scrapbooking. I've purchased them at Michaels and Hobby Lobby. I've seen pictures that were written on the back with a fountain pen and now you can see the writing through the front of the picture. In contrast I have several photographs that are over 100 years old with pencil writing on the back that are still in wonderful condition. Sandy