Acid-free or pH-neutral art papers are used for support as art ground or for layers for permanence.
If infused in water, such paper yields a neutral or slightly basic pH - 7 or higher, and usually free of lignin and sulfur.
- Lignin turn yellow in heat, resulting in yellowing paper.
- Acid makes the paper more brittle over time.
Archival paper allows preserving artwork for long periods, hundreds of years.