No, just thinner medium. I'm never using enough at once or having it sit in a tray or on a pallet long enough to need retarder. If you're painting miniatures or something and your have a whole bunch of it you're dipping out of for a while maybe you would need retarder I don't know. For the most part if I'm brushing I'm just doing small detail stuff and only using a few drops of it. That being said I airbrush a lot so if you're dipping into it and doing a lot of brushing like an interior or something you might need retarder.