However, if you are not that picky, you could just assign each person a number. Use pH Neutral paper, inks and adhesives. The pH scale ranges from 1.0 to 10.0 with 7.0 as neutral. A pH level below 7.0 is acidic. A pH above 7.0 is alkaline.
Nothing is truly acid free.
Most products are virtually acid free. This means they have a pH level close to 7.0. Companies are allowed to claim this as long as their papers are close to 7.0. Also, too much alkaline is just as harmful. This buffering helps keep the acid from memorabilia and photos from migrating onto other items on the page.