I think that the restoration ceases to be the work of the original artist and start to be the work of the restorers when first, the art they are restoring loses the original intent of the original artist. Also, I think that when the form of the art and visual techniques are altered in some kind of way, then it becomes the work of the restorers.
When an artist makes a work of art, they have a purpose for the viewer to feel. They want to give you some sort of feeling toward the art, and when the restorers change the art until the point where the original impression is gone, then the work ceases to be the work of the original artist. It is true that for each person who sees the painting the impressi