You said "not" machine made, implying some irregularities...then is it possible that these are aggregations of animals/plants/? or an individual animal's body part? Think compound-eye, Tapeworm scolex, leech-type sucker mouth, or even a layer of insect "skin", wing, etc?
When the piece is viewed up close it appears that the blue parts are not a background, but material that maintains the black spots in place against a clear substrate, Perhaps previously wet or gelatinous maybe?