These cards have been marked using a special kind of juice formula. These cards are great for magic tricks and can be seen, by you, from up to 15 feet away. These cards are hard to read and you have to train your eyes to be able to read them. It can take anywhere from an hour to a week to learn to see these markings. Since they are so hard to see it would almost be impossible for a spectator to see. When someone first showed me these cards I was amazed how easily they could tell what number the card was, when I was finally taught how to read them it took me about 2 hours to see them. I have now had these cards for about a year and even the light marks stand out like neon signs. These cards come with full instructions on how to read these marks and how to use them. These cards can not be detected using the infamous riffle test. The harder they look the harder it is to see, even under bright lights and close inspection. You do not need any kind of glasses or special devices, and you don\\\'t have to look at the