I was playing around with shapes and lines. At first there were only Queen and Knight and I thought it would be interesting to draw some more to make them into a Chess set. I actually only know the basic of Chess so most of the ideas came from their names literally.
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I made some changes after looking through your comments, which are very useful and inspiring. The biggest problem is their silhouettes are very similar and hard to recognize. I hope the changes are better, but may still not enough.