I was looking at my UK penny's and noticed one of them had an imprint of King George on the reverse. I am curious as to how this happened. It appears to be two coins caught and struck together. What do Y'all think.
Not just common, but almost impossible to find examples between 1911 and 1920 without ghosting! It came about because the bust was in too much relief for the minting process at the time, resulting in insufficient metal being left to complete the reverse. Various attempts were made to correct the problem by tinkering with the design.
Ghosting is not considered an "error", as it is a nearly-inevitable outcome of a combination of high-speed minting processes and coin design. It is often seen on coins that are large, relatively thin, and have a high-relief design on one or both sides.
It's also why most modern coins do not have high-relief designs.
While ghosting can resemble a die clash, there are clear differences. On a die clash, the mirror-reversed design has a clear, sharp edge; with ghosting, the edge is blurred and fuzzy (like a ghost).
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis