I've messed around a little with Plainsman's Polar Ice, it comes extremely wet also. This is from their website and the reason behind mixing it so wet. No clue if this is the same reason for your black porcelain being so wet but I was wondering if you dried it out a bit more if it would actually increase the plasticity like the Polar Ice does. Did they let you know which stain they are using for part of the black colour?
"Polar Ice has extremely high plasticity (to properly pug it we must run it too soft). Others claim to be plastic, but they use the word in a relative sense (meaning a little less flabby than that other really flabby porcelain). Do not attempt to use Polar Ice if it is too soft (stiffen it before use to experience its full plasticity). To reduce the water content wedge it and flatten down onto a very clean plaster table or large bat (or you may be able to leave a lump under a cloth over night or longer).
The most prominent side effect of the plasticity is its stickiness, this body is extremely sticky. It will stick to your hands, to the table, to the cutting wire, anything that touches it. During trimming it will stick back to itself and tools. If you attach ware to the wheelhead with water to trim, it will stick fast there also. After trimming it balls up under your fingers if you attempt to round corners by pressing on them. However if you stiffen the body to optimal throwing stiffness, it will be much less sticky."