What was used to prevent african american men from voting in late 1800s?

A law was created where you could only a man could vote if their grandfather voted prior to the time they were supposed to vote. This was called the "Grandfather Clause." African-Americans were politically shamed upon as people of that time period thought that whites were superior to all races and ethnic groups. So when Whites in the government came up with the Grandfather clause they knew that not one African-Americans grandfather would have been able to vote prior to then. The law was a perfect way to limit the African-Americans without seeming totally racist.