It's nearly impossible to replicate the original bead quirk with a skim coat using a trowel. It was done with a special cutting tool. The plaster was coated out thickly,, flush to the edge of the bullnosed bead, then the quirk tool cut the small "V" shaped indent, either side of the wooden bead. It's a small metal tool that has a rounded shape to run up the spine of the beading to keep the shape constant, it has a small pointed "beak", that cuts into the plaster. It was done to hide the crack either side of the wood bead, that you will always get between timber and plaster. A skim coat is not thick enough to give a neatly finished quirk. People nowadays tend to square them off using beads,, but i think that neatly done quirks, either side of a nice looking, timber bullnosed beading looks good.