The process for restoring paintings depends on the damage. The first step is always to assess the canvas to understand the full scope of the current condition.
Usually the restoration work begins with the removal of the existing varnish. Once the varnish has been removed any patching of the canvas can be performed and any necessary re-touching of the painting.
After a suitable drying period a new layer of varnish can be applied which again is left to dry.
The process differs slightly for paintings of different mediums – oils, acrylics, watercolours.