Tom Norton's Walnut Darkening Medium is an additive to be used to darken the original Walnut Drawing ink when a drawing needs that extra punch. Some artists will add black India ink to darken the color of Walnut Ink. This will work, but loses the tonality of the beautiful brown ink and sacrifices the unique watercolor characteristics of the ink, also losing the ability to lift color or lighten areas. The Darkening Medium is very heavily pigmented and made with the same binder as the original so it can be added or mixed with Tom Norton's Original Ink without changing its working properties. It can also be used straight from the bottle. However, it is so heavily pigmented it will behave more like a Sumi ink and stain the paper and not lift as easily as the original.