A picture frame is a decorative surround edge, usually made of wood that is used to enhance and protect an artwork. Together with the mount and glass they are there to protect exhibited artworks from environmental damage. Examples of environmental damage are acid, damp and light. Artworks that are stored under normal humidity conditions away from light and separated by acid free paper will retain their original condition for longer.
Framing to a preservation standard means creating an acid free sandwich in which the artwork is not exposed or in contact with acid.
Acid is a byproduct of the breakdown of lignin. Lignin is present as a binder in all wood. All mount card that are made from wood will potentially have a Lignin content. Today most mount cards have been chemically treated to remove the lignin and are pH neutral. Manufactures guarantee that the core of white core card will stay white for 25 years. Studies have suggested that today’s PH neutral materials that all good framers use will last up to 100 years without perceivable acid damage.
You can spot the tell-tale signs of acid damage in older framed artworks by the brown staining on the paper and bevel edge of the mountcard and a brittleness in the paper. These are a thing of the past as all materials used today are PH neutral, so its not really a concern.
Your framer should advise you on using the more costly cotton based mountcards if your artwork is of greater value.
Museum grade mountcard
Museum grade mountcard made from cotton fibre is truly acid free, more expensive but will last much longer.