A sketch from a photo of Alan Watts using dilute Lexington Gray ink in a waterbrush, which enables shading to be quickly added as layers of ink are built up in to different tones.
This ink made by Noodler’s is usually only available in the US, but recently supplies have been available in the UK.
Distilled water is best for diluting the ink as it keeps an even flow through the waterbrush, though tap water is fine.
The great thing about Lexington Gray is that it’s suitable for fountain pens but is also permanent once it contacts the cellulose of the paper. This means a wash or watercolour can be added to ink drawings. This would usually only be possible if Indian ink was used. Indian ink contains shellac which sets hard and makes the ink waterproof on paper but can destroy a fountain pen if left to dry.