I gild the bevels of my archival mat boards, and I am wondering if this affects their archival-ness. I use acrylic paint, water-based size, and 23K or other genuine gold leaf.
There is always a chance, slim, but it exists whenever introducing any foreign material to another. Because the element of water, and location near the artwork (both acrylic paint and water-based size) a proper period of time should be allowed before actually using the mat and I assume final framing. You can always introduce a secondary 2 ply acid free mat attached between the bottom of the over mat and the artwork, this will reduce the chance of any contact. Martin Kotler
I am sure you are purchasing and using good quality archival mat boards but it might be worthwhile for you to read over our section regarding archival paper products in our “Flexible Supports” document that can be found in the Resources section. I am assuming you are first toning the surface with the acrylic paint? As far as the gold leaf is concerned you really want to avoid potential formation of corrosion down the line if you are using anything other than 22-24K. If your alloy contains copper and your artwork gets exposed to humid environments or even direct contact with water (lets hope that doesn’t happen), the paper-acrylic-size layer beneath your gold will likely react with any copper that is present and could eventually lead to the formation of corrosion products and even flaking. While this could still potentially happen with 22 and 23K, it is less likely to be a problem in the long run.