2 months of UV/Lightfastness testing. I used inks on hand and sliced down the middle after making 2 columns. The "W" columns were dipped in water to show a quick water resistance
Black Drawing ink Indian Ink Calligraphy Art Design Colour Wash, Line Drawing | eBay
Artist Drawing Ink 20g Jars Koh I Noor 7 Colours Lightfast - Etsy UK
Octopus Write and Draw Ink 403 Violet Lion Waterproof Ink for Writing and Drawing Calligraphy Ink, Lightfast Drawing Ink for Fountain Pens, Purple, 50 ml : Amazon.co.uk: Stationery & Office Supplies
Koh-I-Noor Drawing Inks – Ross Art and Craft
Rohrer & Klingner SketchINK® - 50ml bottles – The Art Trading Company
Qualities of Metallic Ink on Black Watercolour- Jackson's Art Blog