Hi, im painting my 1/48 model spitfire and im fairly happy with the camouflage part, im now painting underneath with a pale green colour paint. im using acrylic paint but im getting hard lumps appearing here and the on my model where ive painted. why is this please? do i need to stir the paint in the pot it comes in more or what i dont know. heres a picture of what ive done http://s895.photobucket.com/user/alecras234/media/WP_20140406_0011_zpsb95cb230.jpg.html