Drawing Gum in a pen. To create even, fine lines these pens disperse a peelable solution used to keep areas of artwork free from water-based colour such as ink, watercolour, diluted gouache. Use on paper, cardboard, Bristol board, acetate, wood. Apply colour when the drawing gum is dry. Once the colours are completely dry just rub the gum with your finger or with an eraser to reveal the masked parts. Available in 2 nib widths: 0.7mm and 4mm.