The chemicals in the flip will break down and a greens slime will form on the coin. Then the slime will start to corroded and damage your coins
But it doesn't always look like that. It can be many different colors, from white to green to brown. It depends on how long the substance has been on the coin. And it's not always slimy, it can also get to be dry and flaky, again depending on time. But what it will do to your coins is always the same - it will harm them.
