Iutsushi means to "cast a copy from," This refers to casting a coin from a circulating coin. In Japan during the medieval period up into the early 1600s Chinese coins, mainly Song and Ming, were imported in great quantities and were the common currency in Japan. People in Japan frequently cast more coins from these circulating coins. Because circulating coins are less crisp than mother coins and also smaller due to shrinkage in the metal when it cools, iutsushi coins are smaller and the character quality overall is softer and more blurry. Nevertheless, it is very difficult to judge whether a coin is merely a worn down Chinese coin (each of which comes in a variety of sizes, script styles and metal content), a Japanese bitasen, a Chinese private counterfeit, a Vietnamese copy.... This is where the collecting and identification get very tough. What I present below is the best I can do at the moment but may contain some inaccuracies. Basically you look for smaller size, differing metal content and casting quality, and frequently a nearly smooth reverse. But metal content varies in even the standard mints, worn coins get smooth backs and soft characters etc... Eiraku Tsuuhou This coin may just be a normal Chinese Yong Le Tong Bao. However the copper color is more common in Japan and there is a certain softness to the edges and blending to the inner rim that suggest it may be a high quality iutsushi.