Have you ever visited someone for dinner and had to put up with them making a huge deal over passing the silver tableware? They may have even gone as far as to stress that it is solid silver, and you will have a tendency to believe them.
Well, strictly speaking they are not telling the truth.
Instead, silver in its natural state is simply too soft and it would lead to bashes and dents in your fancy tableware. So, what they do is they mix it with a base metal, which is usually copper, but only in small amounts in order to give it that firmness. Generally speaking, you are looking at 92.5% silver and the rest made up of the other metal.
So, the next time they boast about their solid silver items, you can fire back that they are only 92.5% solid silver and see what kind of a reaction you then get from them.