We follow a paper trail back in time to learn about the laborers -- some of them enslaved -- who put their backs into the graceful old building that now houses the National Portrait Gallery.When construction began on the building in the 1830s, Washington D.C. was in the midst of a mini building boom as a seat of freedom and democracy. Yet the city also had an active slave trade. By sifting through reams of microfilm and estate records, historian Michael Hussey was able to establish that at least 17 men who worked at this site were enslaved. His next step was to try to sketch a portrait, however faint, of one of their lives.