A local group that works to restore Revere’s Rumney Marsh Burial Ground is holding a ceremony next Saturday at noon to unveil two stone tablets it is installing at the historic cemetery on Butler Street. The tablets are in memory of 13 18th-century slaves, as well as an African-American Revolutionary War veteran and his wife, all of whom are buried in unmarked graves in the cemetery. The markers contain information through research by the Rumney Marsh Burial Ground Restoration Committee, according to Jeff Pearlman, the committee’s historian. The event is timed to commemorate the 150th anniversary of the Emancipation Proclamation, said Pearlman, whose group raises private funds for restoration work at the cemetery. City officials and area legislators are expected to be at Saturday’s event, which will include a skit performed by students from the Whelan Elementary School, a performance by a student percussion band from Rumney Marsh Academy, and a talk by three Revere High School students on Abraham Lincoln and slavery. The event is free and open to all.