Forgery, Underneath the deceptive patina Thánh Nguyên Thông Bảo, 聖元通寶 There is only one known type of a full size Thánh Nguyên Thông Bảo coin, which is attributed to Hồ Quý Ly of the Hồ dynasty. The coin is both rare and hard to find. The piece shown in the figure to the right was picked from a box of Vietnamese coins all priced at about $10 so common sense suggests the coin is not genuine, but stranger things have happened. The basic design of this piece is similar to the real coin but the calligraphy is not correct, particularly the character Nguyên, and the character Bảo, which does not have the hooked right foot that is characteristic of the real coin. This forgery is also interesting because of its appealing red and green patina, which appears genuine at first sight. However, scraping the patina reveals that it is easily removed and artificial. Scraping also reveals that the patina was made of two layers, a base layer of red patina that adheres well to the metal, and a second dark green layer on top. These layers are not characteristic of most natural growth patterns of red and green patina. Natural red and green patinas usually grow together in a single uniform layer with red and green regions that can only be distinguished by their color. A rubbing of an identical coin has appeared in a recent Japanese work on Vietnamese coins.