Glasses that can see through playing cards
There are infrared contact lenses and glasses that can see through playing cards. Normally, customers who are first time to buy marked cards products will prefer to buy infrared sunglasses, while the clients who often play casino game will prefer to buy infrared contact lenses.
Why they will make a different choice in buying marked cards glasses? That is because the green just buy for trying, not for increase their winning odds in gamble game.
How IR contact lenses and glasses see through playing cards? According to light reflection, human eyes can not see infrared ray light and x-ray light, to absorb the lights we can not see, some technician invented infrared contact lenses and glasses. That is why we can not see the invisible ink marks on playing cards, but we can see through them by marked cards contact lenses and glasses.