The product is a US 1981 Scott # 1858 Plate Block of 4 MNH 18c featuring George Mason as part of the Great Americans Issue. This dark blue stamp from the United States is in Mint Never Hinged quality and is graded as XF (Extremely Fine). The certification is not mentioned, but the stamp is from the United States and is a valuable addition to any stamp collection focusing on American history and famous figures.