This rather battered and bruised object is a mummy mask that was found at Giza and dates to the 5th or 6th Dynasty in the Old Kingdom – so it’s a bit over 4000 years old! Not entirely surprising that a plaster object like this might not be in the best condition.
There’s not much info on this from the Brooklyn Museum (acc. no.: 48.183), so I don’t know if it would once have been painted to look more realistic or not (my guess is it probably was). Nor do I know if it was found on the actual mummy (probably not).
They do say in passing in their “ask the museum” section that it was moulded directly onto the mummy, but isn’t a cast of the real person’s face. And that this practice was only in fashion for a short period.
See it on my photo site: https://photos.talesfromthetwolands.org/picture.php?/74/