I am on a quest in search for a white, waterproof pen that reliably lays down a thin, opaque line. You’d think that this wouldn’t be so hard to find, but this combination (opaque-and-thin-and-waterproof-and-reliable) has so far proven to be elusive. The closest so far has been the Uni-ball Signo Broad UMR-153 white gel ink pen, but it tends to dry out and blob, so it is far from perfect.

The Uni Do! Posca paint marker in white, extra fine (0.7) is a welcome addition to the white pen field. It’s waterproof, water-based (so not smelly like other paint markers), lightfast, and can be used on a multitude of surfaces. I’m going to focus its use on paper, but if you’re looking for a way to label a dark coloured object, this may be the pen for you.

The Do! Posca’s design is pretty well designed. The pen is narrow enough in diameter for you to comfortably use it like a regular pen, and the square cap keeps the pen from rolling off the table, and looks great. The pen body is much too busy for my liking, but that’s a minor quibble.

There’s a tiny metal ball inside the pen, and you need to shake it well before use to get the paint ink flowing. When you use the Do! Posca for the first time you need to prime it by shaking the pen thoroughly and then pressing the plastic tip in several times until the white paint flows. I had no problem getting the pen to start up after a good shake, but I’d recommend keeping it horizontally and cap it immediately after use.

The Uni Do! Posca doesn’t blob, and it’s excellent for small details. I wouldn’t use it to fill in large expanses of white, as it offers pretty poor coverage and doesn’t layer well. If you’re looking to use it for highlights, correction or detail work, this is the pen for you.

I drew this journal comic on a Clairefontaine Paint On Naturel A5 pad.

The Uni Do! Posca extra fine paint marker in white was available for a time at Jetpens, but now you can find it easily enough on eBay. If you’re looking for an opaque, extra fine, waterproof white pen, I highly recommend it.