How do you turn satin paint into flat paint?

I prefer to paint all walls and ceilings satin. I have no idea why people just automatically think that ceilings have to be flat...or even white. I do satin on the ceilings because of dust, yes dust does stick to the ceilings, esp near AC vents and around ceiling fans. Have you ever tried to sweep your flat white ceiling to get the dust off after a few years? It just smears. I think satin ceilings make small rooms brighter and larger. You must use satin or semi on the ceiling in the bathrooms, a bathroom environment is the one interior space that is actually most like an outdoor space with water splashing, steam, humidity, extreme temp changes, I wonder if it would be best to use exterior paint in the bathroom. For ceilings though I pick a white with a bit of grey and go all satin.