Will not work. The baby powder will leave aged marks like decomposing crete. People use it to get the "aged" look in new crete.
Paws

talc can be used as a release agent when using a press-mould for clay, maybe that's what you heard about?

interesting about it giving an aged look. must try that. I guess it works by absorbing the moisture from the top layer of the cement, preventing hydration?

Paws, Never heard about baby powder but Tango talked about using baking powder for the ancient look. Don't remember the exact name/description but it takes up space in the mold and gives an uneven, aged looked. Didn't he use a spray on release and then the baking powder adhered to the spray. Would certainly be cheaper than baby powder. Billie

Not sure about the spray on release. I think the powder ( mine was really old, found it in the closet) reactes chemically to the crete or something. I tried it once but used too much. It was hard to see much detail in the piece, a mask. Live and learn.
Paws