Oil paintings take me about 3 or 4 weeks to complete, and sometimes longer. Therefore quite often, in between oil paintings, I use water-based media, which is so much quicker. From deciding on a composition to completing it takes me 2 or 3 days. At the moment I really like using acrylic pigmented inks. Contrary to “normal” inks, which can be fugitive, ie fade in daylight, these inks have a good lightfastness rating. I prefer transparent colours. Waterproof when dry, colours can be layered without disturbing previous coats. I loved Rotring Artist’s Colors, but they are discontinued. They were transparent and lightfast (I still have glass which I painted about 25 years ago, so I know the colours were lightfast for at least 25 years even when hanging in a window). Still, other reputable firms now make acrylic pigmented inks, so I’m sure they’ll withstand the test of time.