This is the helmet I have for my bike I'm building

Its a military surplus steel pot helmet, I got it pretty cheap since it was a un observer helmet and thus blaze orange. 2 coats of black and 2 more coats of the same red as my bike.

First thing was I used a sharpie to sketch out a rough checker pattern on the helmet. I was going to try and measure it all down make it perfect. I had a rig all set up to make the perfect arch... but it didnt work so I eye balled it. I then filled in the patern with several coats of alternating white and black. I then got some paint markers and outlined the whole arch in black and went about neatening up the edges.

For the other side I wanted something Orky and Meky I found a geared ork skull online and made a stencil. I then traced that onto the helmet with sharpie. I painted in the gear and skull in white and then used the black paint markers to fill in the eyes nose and give it some nice outline