A better look at the Hartley & Noble drape forms with Giffin Grip mount 

Thanks. I've only used sodium silicate as a deflocculant, never sodium carbonate, but you're absolutely right about it reducing the shrinkage by reducing the required water. I don't usually bother using it as it adds complexity and the shrinkage isn't an issue for most of my work, but it's a good solution when that isn't the case

Depends on a bunch of factors, like how dry the clay is at the start, the heat and humidity in the room, etc. A few hours to overnight should be a good starting point

MDF