Justine Haupt, the polymath behind that killer rotary cell phone, has a lot of other tricks up her sleeve. On her projects page I found this concertina (an accordion relative) that she 3D printed, as you can tell by looking at it:
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However, the finished product rather convincingly resembles wood:
So how’d she do it? In a nutshell, some 60-grit, stain, wood finish and (directional) elbow grease.
You might be able to figure it out from there, but click here for details on her process. It’s as simple as it is clever.