Quote Originally Posted by gandolfi View Post
Thanks PE. That does make sense.

But it doesn't explain why it looks like the image isn't bleached away. It is not that the bleach is exhausted I think, as the deepest blacks are gone - but the "middletones" and highlights seems to stay..
What you are seeing is a partial image of Silver Sulfide that remains behind due to extremely high density in original Silver metal. If it is Ag2S, it cannot be removed.

My guess anyhow.