Not an expert by any means but when i was painting my purifiers i had a lot more success with the white helmets by not painting the pure white . Here ' s my methodBase coat with celestra grey . Build up with thin layers if painting over dark surface . Shade recesses with colour of choice , in your case drakenhoff nightshade ascit produces the cool white you want . Re apply thin coat of celestra over helmet leaving recesses as they are . For this step and beyond the thinner your layers are the smoother a result you can achieve . Highlight with ulthuan grey . Apply thin coats to the helmet focusing on raised areas and leaving some celestra towards the recesses . Finally edge highlight with your choice of pure white paint . It is good to use thin paint for this step as well and will produce a very crisp result . Most important i find to avoid the chalky appearance is to paint on your layers thin and let them dry before touching them again . The more you bugger around with the paint while its wet the chalkier it will appear . Happy painting mate and keep up the good work