>My understanding speaking to Hiroe Hanazono is that in terra cottas the iron content doesn't affect the slip, but that in stoneware it can... Go figure?
I found this statement in a Digitalfire article on low-fire terrcotta casting slip
Adding iron oxide to a clay causes it to gel badly on dispersion however the natural form of iron in Redart does not do this at all.
So perhaps it depends on how the iron gets into the body, in a red clay or as iron oxide. [Hand-waving hypothesis.]
Have you tried adding more deflocculant to a small sample of your body? Does it thin it further? How does it modify the gelling issues?