"If a film starts covering your powders it's mostly from oils that have accumulated from the tools you've used whether it's fingers, brushes or powder puff. The powder stops being efficient after a while because of this hard film. The solution is to take a strip of clear packaging tape and press it down on the powder, rub your finger over the non-sticky part. When you lift the tape you'll have revived the powder so that it's no longer hard and you can use it again.