(1) Could casting these small pieces "on the half-shell" (split up the median) then assembling them in greenware be doable/useful?As many ceramic collectors already know, earthenware horses have historically been cast whole. This is how Hagen-Renaker made their horses, and then later how Joan did most of the production horses at Pour Horse.
(2) Perhaps cutting problematic legs off, probably in the triceps area and biceps area (so they "lock" better) and casting as separate pieces might be the only way around it?
But European bone china and porcelain have a different tradition, one where the horses are cast in pieces and reassembled. After Joan formed Marcherware with Mark Farmer of Alchemy, she began experimenting with assembled pieces. The process makes it possible to cast more complicated horses. Horses with twisty bodies and swirly hair bits - Sarah's specialties! It also makes it possible to cast much larger horses than we've done before, because the individual molds are more managable. (A whole-body mold of a traditional-scale horse, when wet, is too heavy for most of us to lift.)
But this is all a rather new direction, and we're still learning what might and might not work. Doing it on a small-scale horse like Vixen or Taboo is something that hasn't been tried. We don't know quite what to expect, or which approaches might work best.
So back to Sarah's comments. These are the things that I have been pondering lately while making (properly soaped) production molds for Imp. Having clayed Vixen up (four times), it's really clear to me that her extreme head turn is going to make whole-casting problematic. Her body just occupies so many different planes. I don't think she will work without cutting her up somehow.
And I had thought about Sarah's first suggestion, which is cutting her in half down the dorsal line. This is how the horses used by military figurines are made, though of course those are typically made from injection molded plastic. And I would need to exclude her neck and head, since it would be really hard to work in that area (to fuse the two halves) without damaging her face. I'm also not sure that it will help with her because bends so much.
What I think will work with her is removing her forehand. Or rather, removing her head, neck and left leg and shoulder. That way my fuse line falls predominantly to the chest and underside of the horse (where any shadows created by the fuse line might be less visible). And I can pour the piece through the big opening of the body.
Of course, I could get lucky a second time. Maybe she will work with just an inset piece over her turned head. I'm going to pour a number of rubber copies, because I think it's going to take some experimenting to find what will work. But she looks like the kind of piece that might push the envelope a little, and that's always good.