Two very important daguerreotypes (an early photographic process) were purchased in the 1990s. The first was of African American abolitionist and former slave Frederick Douglass, acquired in 1990. It is one of only four daguerreotypes of Douglass known to exist. That year, the number of images in the museum's photography collection reached 8,500 objects. Six years later, the NPG obtained for $115,000 the earliest known daguerreotype of abolitionist John Brown, whose 1859 raid on Harpers Ferry helped to spark the Civil War. The portrait was created by African American photographer Augustus Washington.