This primary source comes from the Records of the Immigration and Naturalization Service.
Full Citation: Cerification of Testimony of Joseph and David Kalf; 11/8/1892; 52727/002; Alien Contract Labor Investigation: Belgian and Dutch Diamond Cutters, 1893 - 1895; Subject and Policy Files, 1893 - 1957; Records of the Immigration and Naturalization Service, Record Group 85; National Archives at Washington, D.C.. [Online Version, https://docsteach.org/documents/document/cerification-testimony-joseph-david-kalf, May 5, 2024]