Waterproof vs Non-Waterproof Inks

When the distinction matters, when it doesn't, and what happens when you get it wrong.

Most beginners encounter this distinction too late — after they've applied a watercolour wash over a carefully inked line and watched it dissolve into the paper. The distinction between waterproof and non-waterproof inks is easy to understand and practically important the moment you work in any mixed media.

What waterproof actually means

A waterproof ink has been formulated so that once the ink has dried on the paper, it resists water. If you apply a wet brush or a watercolour wash over a dried line, the line holds. The waterproofing is achieved through different mechanisms depending on the ink — some use shellac, some use resin, some use a chemical bonding process — but the practical outcome is the same: the line survives water.

Non-waterproof inks are dye-based. The dye is dissolved in water and sits in solution. When dry, the dye is bound loosely to the paper fibres and can be re-dissolved by water. A wet brush applied over a dried non-waterproof line will lift and move the dye.

When it matters

If you draw with a pen and then apply any kind of water-based medium over the linework — watercolour, ink wash, even a damp cloth — you need waterproof ink for the lines you want to keep. This applies to manga artists who use brush washes for toning, botanical illustrators who apply watercolour over pen linework, and illustrators working in any mixed media.

If you are making work where the line is the finished piece — no washes, no water-based media applied afterward — the distinction is irrelevant. A non-waterproof ink can make a beautiful finished line drawing that will never be touched by water.

When it doesn't matter

For sketching and journalling. For fountain pen writing. For loose illustration work where washes are not part of the process. For ink testing and exploration. Non-waterproof inks are often more beautiful in isolation — their shading, sheen, and colour depth can be extraordinary — and there is no reason to choose waterproof inks for work that will never encounter water.

The specific products to know

Waterproof in Inkwell's range: De Atramentis Document series, Diamine Forever series, Deleter Black 4, Dr Ph Martin's Black Star Hi-Carb, Nicker Poster Colour (when used with appropriate paper). These are your inking inks for mixed media work.

Non-waterproof in Inkwell's range: Dominant Industry Standard series, 3 Oysters, Pilot Iroshizuku, most Rohrer & Klingner dye inks. Beautiful for the line. Not for mixed media over washes.

The important timing note

Waterproof when dry means waterproof when fully dry. Fresh De Atramentis Document ink on paper will smear under a wet brush — the waterproofing mechanism requires complete evaporation before it activates. On most papers this takes three to five minutes. On Tomoe River it can take longer. Do not apply a wash over a line you drew thirty seconds ago and then conclude the ink is not waterproof. Give it five minutes.

What to do if you're unsure

Test on a swatch. Apply a line of the ink, let it dry fully, then run a wet brush over it. If the line holds, it's waterproof for your purposes. If it lifts or bleeds, it isn't. This test takes two minutes and prevents every mixed media mistake. Keep a small piece of your working paper for testing. Use it before committing to a finished piece.