I just read this article,
Scientists Help Restore Aging Artworks , on a new development in artwork restoration.
Perhaps we can just list the colours we use on the back of the canvas, then, and all will be ok
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I wonder, though, this going over with actual paint - does it make for merely a very accurate copy. Wouldn't the inimitable genius in the brushtrokes be lost? And then the importance of a piece be lessened. Maybe you are right, Sharon, to cover yourself when to comes to keeping colours true and long-lived when you are creating your own work.