Sculpting Woodgrain

[KnivesVenture]

Hey guys! Okay, so unfortunately I don't have a budget (No Zbrush=Sad) and only have meshmixer at the moment. What I am wanting to do is add a woodgrain design to Majora's Mask. So that it looks sort of like this.

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I've figured out how to invert the stencil in Meshmixer by holding CRT (I know, I am practically an expert at 3D sculpting now *major sarcasm, I am very new at this*), but is there any way for me to draw a perfectly straight line, or a line without the bubble look to it using mesh mixer? If not, is there any free 3d sculpting software out there (other than Blender) that you could point me to?