1. UNIVERSALITY - Acrylic are probably the most versatile of paints. You can thin them with water and use as watercolor (they will remain permanent upon drying, unlike watercolor), apply them in full strength, create textures.
2. COMBINABLE - This medium is very suitable to be combined with anything you wish - watercolor, ink, pencils, oils... Free your imagination and experiment!
3. NUMEROUS SUITABLE SURFACES - Acrylics can be used on paper, canvas, wood, metal and many more surfaces (this is true, even though they don't adhere towards some surfaces as promptly as oils). This is a great advantage, when you get used to this medium, you can paint at whatever material you've got available.
4. DON'T STINK - That's right, all of you that have experienced headaches caused by oil paint might just appreciate an acrylic vacation!
5. FAST DRYING TIME - Composition doesn't seem right after you put down your first layer? This is not a problem, wait half an hour and you can repaint it completely, acrylics dry really fast. On the other hand, make sure you don't waste your paint, keep you palette wet and rather squeeze less paint from tubes. In case you don't consider this fact an advantage, there are long drying time acrylics available as well as numerous retardant agents that can be used to regulate drying time.
6. EASY CLEANUP WITH WATER - Not just your hands and floor will appreciate this fact, but also your clothes and tools. Make sure you take a good care of your brushes, though, once you let acrylic dry between brush hair, you won't get it off!
7. CHEAP - At least compare to oils they really are cheap. Just like every medium, even acrylics can be purchased in artist quality, those get expensive but blend nearly like oils, pleasure to work with such.
8. VARIETY OF COLOR - You will find numerous colors and shades available, and will probably take advantage of pre-mixed colors, since they dry oh-so-fast!
9. FUN & CHANGE - Acrylics are tremendous fun! Also, if you don't work in this medium often, it's a delightful change, something to try out that will surely enrich your skills. Chop chop, music on and dance while you paint

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I'm currently trying out watercolors but acrylics are easy to work with.