I added vents at the ends of the arms. They are cocktail straws, snipped and buried halfway in the clay bed.
At last I’ll finalize the parting line around the piece for the mold halves. Prepare a variety of clay snakes, collect your favorite tools, and find a comfortable place to work with good lighting:
Also, have a good cup of coffee, and listen to Radio La 2×4 Buenos Aries. (http://www.buenosaires.gob.ar/la2x4)
The techniques I think works best is, having built up in a general way close to the piece, to now lay a line of clay along the remaining gap of about the same size as the gap or slightly larger, and simply press it gently into place with small tools.
This neatly fills and seals the gap, without applying pressure onto the piece which will make the clay line difficult to remove cleanly and without blemish to the piece later. The gap must seal completely.
One side done, halfway around.
And finished, including some keys which can help to keep the two halves in alignment. I don’t take keys too seriously like some people. I think the complexity of the plaster mother mold’s shape, is enough to keep the silicone in place, but people expect to see these in a mold so do a little of it, for example. I think channel shaped keys like this do more to help prevent material you pour into the mold, like wax or plastic, from leaking out at the seams while it solidifies.
Next, I’m ready to pour the silicone to form the blanket mold of the first side you see here. Exciting!