Zinc rot. From 1983 onwards the 1 cent coins were changed from 95% Copper to Copper coated zinc. Unfortunately the zinc planchets were not washed well so when they coated the planchets with copper they didn't adhere well and causes the zinc plating blisters/rot like you see here.
Looks like rot, you get gas bubbles under the coating causing this. When you post your pictures please use full image rather than thumbnail, makes it easier for us to see what you are posting. Also please post both sides of your coins when making a post, as there could be clues on the other side to help us help you.
That 6 is interesting. Copper can move or be displaced on a coins surface. The other dots are plating blisters. The Six looks like a plating disturbance. Better photos would help.
Zinc is more chemically active and considered a sacrificial metal. It will oxidize and dissolve away before other types. (Think of zinc anodes on boat motors and water heaters). Since the zinc is more chemically active than the copper it will degrade first. Any type of break in the surface of the copper plating will usually cause the underlying zinc to start to degrade. It can expand as it degrades and produces these large "bubbles". Some can actually resemble volcanos.
@Lueds The examples you have shown occur before they leave the US Mint. What she has occurred after it left the Mint.
Your cent was damaged after it left the mint. Those bumps are plating blisters which are common on these zinc cents. Welcome to CT.
Zincoln cent, period. Sorry, but I really detest the copper coated zinc cents. I wonder if they ever experimented with coloring the zinc to take on a copper look. Might be better than what they currently have.
