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Okay, I'm trying to bake the coloured materials I've added to my model. But whenever I go to the Render tab > Bake > and select any of the options, I get an error at the top saying 'No active UV layer found in the object'. Well... Of course not. I've added materials, not textures. I've not had to do any UV unwrapping. What am I missing? What do I need to do to bake coloured materials?