What an interesting photo OmerH -- and what a challenge it gives us!

Is this one of the approximately 5 blackened steel tiaras made by Cartier in the early years of the twentieth century -- or is it a later creation? Despite having spent a couple of absorbing hours searching for information, I am no nearer solving the question.

For a little while I wondered if what looks like blackened steel might be the Sultanah's hair but I think you are correct and that the dark area is blackened steel.

An interesting find! Hopefully someone will know more than I do and share their knowledge with us, now that you have spotted the photo and the tiara.