Accenting 3D prints with nail polish

Accenting makes prints look finished

Recessed writing or markings need to be filled with paint to make them easier to read and to make the print itself look more finished. A lot of people use Sharpies for this, but I am awful at it and I always colour outside the lines. I recently printed a set of Mini Dominoes (Fig. 1) and wanted to colour the dots, so I tried nail polish.

Figure 1. A set of Mini Dominoes by Hercanstein. I wanted to fill the divots with a unique colour for each value, so six colours in total. I also needed the colour to be wear-resistant, and I wanted the finish to be more professional instead of looking like I coloured it in, which is what Sharpie-accented prints often look like.

Why nail polish?

Because it’s inexpensive and easy to find. It’s durable, it comes in many colours and finishes — matte, gloss, swirls, glittery, glow-in-the-dark, thermochromatic (!!) — it forms a thick, opaque layer, and it dries reasonably quickly.

The nail polish I got was the cheapest set of colours I could find on eBay, basically. It came with 12 colours which was nice, but the best thing about them was that they had both brush and “pen” applicators (Fig. 2). The pen applicator is what I was really interested in; it’s a hollow needle that lets me apply the nail polish very precisely.

Figure 2. Inexpensive nail polish from eBay. Each bottle comes with a hollow needle applicator (right). The needle is 0.7 mm OD. There is also a brush applicator that you can access by unscrewing the entire top part from the bottle.

Result

Figure 3. Painted mini dominoes. The colours are really bright and glossy. I actually regret using black to colour the 3-dot sides because a brighter colour would have been much cooler.

Figure 4. Detail of the painting. I put a large drop of nail polish in each divot so that it was beading above the surface of the domino, and it subsided into a thick coating along the surface of the plastic.

I love the colours and the effect of the nail polish. I tried to get away with using a Sharpie to mark the center line of each domino, but it just looked awful beside the coloured dots that I had already placed. The gloss and thickness of the paint really does make the print look like it was finished with care (Fig. 3).

The colours I like most are the ones that have really fine glitter mixed into them, which is the blue and purple in Figure 4. The glitter diffuses the light and makes the glossiness more even and gentle.

Parting tips

This technique worked great for me, and I hope I’ve encouraged others to try it too. Here are some random things that I learned while I was doing this:

1. Remember to mix your paint. I totally forgot for the first half of the job, which is part of the reason why values 1–3 (yellow, green, black) look a little uneven.
2. If you need to fill a channel with colour, use a back-and-forth scrubbing motion. Place a dot, push it backwards. It helps get the paint into the corners and onto the sides of the channel.
3. Apply a thick layer. Your nail polish should form a bead that is proud of the surface of the print. As it dries, it will shrink and coat the surface.
4. This may or may not work on ABS. Nail polish has solvents that may damage the surface of an ABS print. However, since the amount of paint you’re applying is so small, it might have no effect at all. If you try it, please let me know!