What is marked cards invisible ink?

Invisible ink marked cards are popular among poker players. Invisible ink marked cards are made by marked cards invisible ink.
What is marked cards invisible ink? As you can see, we cannot see anything while we use these magic marked cards poker cheating in poker cards games. We need to get the help of infrared contact lenses or UV invisible ink marked cards contact lenses that can see invisible ink markings clearly. You will find that you are falling in love with these cheating playing cards devices tricks.