Some of the dual metal build coins suffer from faults when they are exposed to cold environments. Once can test for this by placing the coin inside a freezer an

Some of the dual metal build coins suffer from faults when they are exposed to cold environments. Once can test for this by placing the coin inside a freezer and observing one of the metals shrink to the point where it disconnects from the other part of the coin. There are much older examples of latent image technology on coins, for example Russian 10 ruble circa year 2000 (look at the middle area of the '0' character): https://thumbs.dreamstime.com/z/coin-rubles-russian-commemorative-edition-31451612.jpg https://thumbs.dreamstime.com/z/coin-rubles-russian-commemor...