Archaeologists excavating the site of the nation's first presidential mansion have found a trove of 19th-century clay pipe fragments, including one bowl depicting a stereotyped African head.

The pipe fragments, uncovered earlier this week, probably date from the mid-19th century and are therefore not connected directly with the President's House, located at Sixth and Market Streets, the archaeologists said.

But the find is of particular interest, they said, because the focus of the excavation is on the house occupied by George Washington, his family and at least nine slaves during the 1790s. John Adams, Washington's successor, also lived in the house; he was staunchly anti-slavery.

Jed Levin, an archaeologist with the National Park Service, which is conducting the dig in partnership with the city, noted that "one important component" of the project "is the exploration of the racial and racist legacy that allowed human bondage" at the birth of the nation.

"In that context, this [pipe bowl] has relevance in a concrete and material way," Levin said. "It demonstrates the continuing legacy of racism."

Levin and other archaeologists speculated that the pipe and fragments were breakage tossed into the basement of one of the commercial buildings erected on the site after demolition of the President's House in 1832.

Levin said such "Negro-head pipes" and other decorative pipes were quite popular in the middle of the 19th century.

In a related development, Independence National Historical Park officials said the excavation site would remain open this weekend from 9 a.m. to 5 p.m. to accommodate burgeoning public interest in viewing the work.

A public platform has been erected on Market Street. Park rangers will be on hand to describe what has been uncovered so far.

Previously open only on weekdays, the site was opened last weekend and drew 1,000 visitors, officials said.

Next week, archaeologists expect to begin excavating so-called shaft features on the site - old wells and privies.

If any artifacts from the time of Washington and Adams have survived, they could turn up in those locations.