for postage. All stamps issued in decimal currency remain, for now, valid at their face value, including those priced in half penny increments. Pre-2022 definitive stamps will be demonetized on 31 July 2023 (extended for six months from the original deadline of 31 January). They can be submitted to Royal Mail to be exchanged for replacement stamps of the same value; these will be new definitive stamps featuring 2D barcodes which were introduced in early 2022 to reduce counterfeiting and stamp reuse. Christmas stamps and special issue stamps will not be demonetized, although from 2022 onwards, Christmas stamps will also feature 2D barcodes. United States United States postage stamps have been demonetized only twice. The first time was in 1851, when the 5-cent and 10-cent stamps of the 1847 issue were declared invalid as of July 1 by the Act of March 3, 1851 reducing the normal letter rate from five to three cents. A few dozen covers are known that carry 1847 stamps after the demonetization date; as stamp usage was then still optional (it would not be made mandatory until 1855), the demonetization seems to have had relatively little impact. The second, more serious, demonetization was prompted by the outbreak of the American Civil War in 1861. Southern post offices held substantial U.S. assets in the form of their stamp stocks, and the Confederates could theoretically have brought in some income by selling those stamps to private individuals in the North. Although in April 1861 John H. Reagan, postmaster of the CSA, ordered the offices in his charge to return their stamps to Washington D.C., few seem to have done so, and by June 1861 U.S. postmaster-general Montgomery Blair ordered the severance of postal ties and the production of new stamps. In August the stamps of the U.S. 1861 issue began to be distributed throughout the Union, along with orders that postmasters should offer to exchange old stamps for new for a period of six days after giving "public notice through the newspapers and otherwise". After the six-day period was over, that post office was not to recognize the old stamps as paying postage. In addition, postmasters were to accept letters with old stamps from other post offices until set dates, ranging from September 10 in the East, to November 1 from letters arriving from the Far West. (Later the periods were extended for an additional two months.)