2017 Silver Isaac Newton 50p Proof NGC PF69 Fifty Pence Great Britain14 Nov, 2023 in silver tagged britain / fifty / great / isaac / newton / pence / pf69 / proof / silver by admin Mark Cooper (Trading as Markflorida) has been a front-runner in the coin & bullion industry for over 30 years. Most of our coins are graded to the World Standard known as the’Sheldon Standard’ 1-70.