This post was originally published in 2011
The tips and techniques explained may be outdated.
The skull and crossed pistons mark is a popular adaption of the tradition skull and crossbones symbol and is commonly seen in motorcycle culture, amongst other. Follow this Adobe Illustrator tutorial to create your own underground skull & crossed pistons graphic. We’ll start with a simple sketch, then build up the detail using a range of linework and vector shapes.
Here’s the graphic I’ve put together for this tutorial. The skull and pistons are both made up of simple linework, but with a couple of simple techniques they can really be brought to life. The final illustration would look perfect as a badge or emblem on a motorcycle helmet or the tank of a Harley.
The illustration begins with a sketch with pencil and paper. Draw a centre line and pay close attention to the details of one side of the skull as this can be reflected in the digital stages. Both the skull and piston sketches will be used as a base for the vector illustration.
Place the scanned or photographed sketch in Illustrator and reduce the opacity. Press CMD+2 to lock it into place, then begin tracing the outline of one half and the facial features with the pen tool.
Select all the linework that makes up the first half, copy (CMD+C) and paste in front (CMD+F), then go to Object > Transform > Reflect to flip the design for the opposite side. Select the open point and press CMD+J to join the linework together to form complete shapes.
Increase the stroke weight to around 6pt and align it to the outside using the small icons. Switch the stroke/fill settings for the eyes and nose to fill them with black.
Elsewhere on the artboard draw a triangle. Stretch out the peak to create a long and thin shape. Press the ‘new’ icon at the bottom of the Brushes palette, then select the New Art Brush option. Make sure the arrow in the preview flows in the right direction then press OK.
Draw short lines with the pen tool and add this newly created brush to the stroke. Reduce the stroke weight if necessary to scale down the brush size, then carefully position the paths so they flow seamlessly from the main outline.
Add these short lines in key areas around the skull to give the impression of an inked appearance. This technique is one of those little touches that can really transform an illustration.
Select the main outline, copy (CMD+C) then paste behind (CMD+B). Clear out the stroke colour and give it a white fill to give the illustration a solid background. Group all the elements together.
That’s the skull complete, let’s work on the piston. Draw a rounded rectangle and an oval to generate the basic shape. Toggle outline mode (CMD+Y) to accurately align the two then merge them with the Pathfinder palette.
Use a range of basic shapes from rectangles to circles to fill out the detail of the piston. Select all the object then click the main outline again to make this the key object. Align the items vertically with the Align palette.
Select the Scissors tool and clip the paths where the inner rectangle extends beyond the main outline, then delete out this unwanted linework.
Select the upper most segment of the path with the Direct Selection Tool and make a copy. Paste in a few duplicates of this line and position them within the piston.
Use the Pen tool to draw a flowing curved line. Hold Shift while dragging out the bezier handles to keep everything accurately aligned.
Copy and paste a duplicate of the line then flip it Horizontally with the Reflect option from the Transform menu.
Select and join the two open ends, then extend the vertical line to the piston head, clip the line of the rectangle with the Scissors tool and join everything to make a complete outline.
The paths that make up the right hand side of the piston can be duplicated and flipped onto the left, then all the open points joined together.
Select the outlining path and give it a 6pt stroke weight with the stroke aligned to the outside.
Adjust the stroke weights of the inner detail linework to add variation to the illustration. Use weights of 1pt, 2pt and 3pt for different elements.
Use a long, thin rounded rectangle with max corner radius as a base for the detail on the piston shaft. Delete out certain points with the Direct Selection tool and extend them with the pen tool.
Duplicate a series of triangles and position them together to provide some basic shading to the piston shaft.
A couple of simple lines of various thicknesses on the piston head can help give the appearance of a chrome or shiny finish.
Duplicate the outline and send it to the back as a white background then group all the elements. We now have our complete piston and skull illustrations, let’s combine them!
Our current piston is a little too short to balance well when overlapped, so use the Direct Selection tool to select and drag the points that make up the lower portion to lengthen the piston.
Hold Shift and rotate the piston by 45 degrees, then duplicate and rotate in the opposite direction. Position the skull centrally. Tip: Toggle the Scale Strokes & Effects option in the Preferences window to avoid altering the stroke weights of the skull when scaled up or down.
Select all the objects, then press the down cursor key while holding ALT and Shift. Count the number of times the key is pressed in order to remember the distance used to make the duplicate. Ungroup all the elements of the skull and pistons.
Select all three outlining shapes and merge them together with the pathfinder. Hold Shift while dragging a selection over all the objects to exclude this outline, then delete everything else.
Hold Shift and press the up cursor key by the number you currently have in mind to reposition the outline exactly back into place. Alter the stroke weight to 11pt. This step basically ensures the thickest stroke outlines the whole illustration.
When mocked up on a dark fabric texture the illustration really starts to show off that underground style. Expand all the strokes to make the vector file ready for use as a logo, sticker or badge.