Since the old dark angels vets in robes are gone I decided to add some robes, or as a start just waist down tabards to normal space marines to model vet. sergeants. I picked up the only modeling clay I could find in stock locally which was milliput silver grey. When mixed I get a chunky brittle hard clay substance that I can\'t do anything with. One stick seems okay and I can kinda play with modeling on it, but the other is hard and brittle and when I attempt to mix them it comes up cruddy...anything I try to do makes it crack and break up. Is this a bad putty for modeling, am I doing something wrong, or is it possibly an old batch or something?