The Art Studio's Graphic ProDuo Markers are alcohol-based felt tip pens that are the ideal choice for artists wanting a high-quality, versatile marker. As the name implies, each pen has a different shaped nib at each end - one end is a fine tip and great for small details, while the other is broad and perfect for filling in large blocks of colour. They can be used on all sorts of surfaces like paper, plastic, cloth and metal, as the alcohol in them dries very quickly and stays permanent. You can even blend colours together! Cool Grey 9 is a very dark grey that makes a great alternative to black if you want a slightly lighter tone in your art, and it is great for drawing shadows and other dark spaces.