I don't think we're really concerned about exposure here. You get like a matte spray from a craft store, I think it has some art application, not really sure what its actually meant for, it can easily be looked up if you're worrying about a specific kind. As has been mentioned a thin layer is sprayed onto the backs of the cards so they stick together back to back, then you can stack them in certain ways so you know which card is where and so on.
There is a 'classic' way of doing which I think most people use, I believe there was something released in the early days of the wire that was a replacement for that traditional method that had really good reviews, much less memorisation and all that. Or, again, you could get something thats worth it, like invisible from DM, which should be buried somewhere in his early lecture notes, I mean it, its really really good. I have no idea why it wasn't used instead of the classic way. Theoretically you can do the classic routine, but have the spec spread through and find the one inverted card instead of you, but there are many other, similar routines described too. There is a very well known mentalist/mental magic/magician who turned the same concept into an incredibly mind blowing routine which has a little bit of fame on youtube, though his handling is quite advanced and not particularly practical, its still incredbile.