Daler-Rowney FW Acrylic Artist Ink is an acrylic-based pigmented ink that is water-resistant on most surfaces. All colours have a three- or four-star rating for permanence, meaning that they can be used for permanent display. As well as using them in their raw state, you can dilute them to create subtle washes to which you can then add further layers.  Available in bottles of 29.5ml (with a dispensing lid) or 180ml (with easy pour application lid).  Can be used with brushes, pens or airbrushes.