Good stuff Geo.
Regarding the Milliput - John uses the 'Fine White', which is really designed for repairs to porcelain etc. I find that, apart form sometimes tricky to mix equally, it being white, it can often be too fine, and can crumble or flake, especially when used wet. It also seems to take longer to fully cure than the 'Standard Yellow/Grey' type. (Plain white carton, with red edges, and red lettering 'Milliput', with 'Standard - Yellow / Grey' beneath the title.)
Having used most of the versions over the last forty or so years, I prefer the above 'Standard' type, which is designed for modelling use, and can be wet-moulded, and a really smooth finish achieved, even before sanding, by wiping over with a wet finger tip. It's also better for sanding, drilling, carving etc, as it doesn't crumble or crack when worked.