10c Dark Carmine, Green, Sturgeon Patent Essays (79-E10b, 79-E10c), four essays affixed to front of Oct. 23, 1867 U.S. Patent Office form acknowledging receipt of John M. Sturgeon's alleged improvement in Revenue and Postage stamps", two of the essays are defective and the form itself has some faults, but a great collateral piece with two very desirable examples of this scarce essay, rare and likely unique