Unique Museum Quality carved & signed John B. King shell 14K Gold cameo brooch man's portrait before 1868

Museum Quality carved Sardonyx shell. In the tested 14K Yellow Gold cameo brooch. According to writing on the back - before 1868. Portrait signed on the back-“John B. King • Boitru Deeral(author?)1858(?)”.Measures 1-7/8” tall by 1-1/2” wide - 47 by 37 (mm.). Weight is 17.2 grams. Good Antique condition