I never heard of this before, sounds good. I do a lot of work with concrete (not precast) and to age footpaths, etc., I use a mixture of sugar and water applied to the wet concrete which I then remove with a power washer the following day. It acts as a retardant so the concrete below cures as normal but the very top skin of 'fat' doesnt. When its washed off it exposes the aggregate in the concrete to give an aged look.