Specialist restorers are on hand to ensure the frames can be returned to their original state. But there are many complex issues that need to be considered.
Flood or fire damage or being broken when in transit are the more extreme ends of the spectrum but just the age of a frame can have its own impact.
Depending on the type of frame (mitre joint or lap or half lap joint – see glossary) the wood can move at different rates so there can be a gap which can make it structurally unsound.
Oliver White, head of furniture at conservation firm Plowden & Smith, says: “Most frames are made from wood and unfortunately they can be affected by climate: the wood can expand or contract and can be problematic. It can also affect the gilding or the decoration.”
As well as dealing with restoration of a frame, occasionally a conservator needs to work on a frame due to a change with the picture itself.
White adds: “If an oil painting needs a new stretcher this can sometimes make it too tight to be placed back in its original frame so we have to adjust the aperture.”
If conservation glazing is added to a picture to protect it this can also mean a frame needs adjustment.
White adds: “We encounter patched-up repairs on frames where a missing part of the gilding has just been coloured in with something like Dutch metal brass rather than gold leaf, some are even spray painted. Brass or bronze powder can oxidise over time and go green.
“What might have looked OK when it was originally mended will deteriorate over time.”
Glossary of picture framing terms compiled by restorer Plowden & Smith
■ Lap joint: A type of joint made by overlapping pieces of wood. A half lap joint and mitred lap joint were the traditional picture frames until the 19th century.
■ Mitre joint: Common from the 19th century onwards. It is the standard joint for most professional picture frames.
■ Rebate: The internal ‘lip’ that the picture (plus potentially mount board and/or glazing) sits against within the picture frame. A qualified restorer or framer can ‘build up’ or reduce rebate width and depth.
■ Sight size/ aperture size: The size of the aperture of the frame, which will cover a small amount of the edge of the painting and will be slightly less than the rebate size.
■ Rebate size: Slightly greater than the sight size/aperture size.
■ Compo or composition ornamentation: Made by pressing a thermoplastic compound, typically consisting of powdered chalk mixed with collagen, resin and linseed oil into a mould. This moulded decoration is then applied to a plain timber carcass to mimic hand carved wooden detailing. Popular from the early 19th century onwards.
■ Gesso: Italian for ‘plaster’ a fluid white substance, often made from plaster of paris, chalk, gypsum, or other whiting mixed with glue that is applied to wooden frames to prepare the surface for decorative finishes, including gold leaf.