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If you're undercoating in black, Pebeo black gesso is perfect. It's got plenty of grip, doesn't need to be applied neatly (because it contracts as it dries) and gives a nice smooth finish. It has no fumes or unpleasant odour, and it dries very quickly - especially when the heating's on.It's also ridiculously cheap: a big pot's under a tenner and will get you through hundreds if not thousands of miniatures. I recently bought a second pot after using the first for four years or so; it still has a fair bit left in it, though it's unpredictable in how it squirts out now.