I mainly use them when working with plain gamsol - and use it to "lift" paint when working with cold wax/oils. I first learned about them back in my watercolor days, with an artist Maxine Masterfield, who would fill her oiler boiler with opaque white water based paint such as gouache, etc. I think you could also use an acrylic, but you may need to thin it out with airbrush medium (clean it out well after use - before the paint dries in the fine tip!) and of course you can experiment with mixing a small amount of gamsol with oil paint - about 1:1 - you could try that and see how it works! Great question! The oiler boilers come in a few different gauges - depending on the type of paint you plan to use, you may opt for the larger gauge (smaller number tip).