Are you talking about piping gel? I did it once before, with handwriting, and It was kinda hard for me to see. Maybe someone else with another experience can tell you better.
I've done tons of them...everything from pictures to just writing Happy Birthday........I usually use clear piping gel, you could use colored I suppose, but it would be harder to cover up unless you plan on piping over it in the same color. Are you just wondering how they work?? I just trace over the design.......I would suggest using parchment paper instead of wax paper being that it's heavier...sometimes the wax paper is too flimsy IMO. Then once you have the design traced out in piping gel...flip the paper over onto your cake and smooth a little...I like to use a dry paint brush just to go over the lines lightly..then peel it off carefully being careful not to smudge anything you've just done. Then you should have a light outline on your cake of whatever it is you're doing.......then just trace over it with buttercream and fill in...simple and effective, I think it works great!!!
I don't spray.......and IMO you'd be better off using a regular sheet of computer paper than the wax paper..........that's just my preference...the wax paper can get really soft and hard to handle....especially if you're piping on it for a while it starts to absorb moisture.....if you can get your hands on parchment paper that would work the best. Yes, you're looking for just a thin line to transfer from the paper to the cake.......the paper will still have more gel on it...you can actually use the transfer several times if you need to .
OK, I did the gel transfers this weekend and I must say... it was so cool how my teddy bear cake turned out... the other one turned out ok but would have been better if I would have remembered to put cooking spray on the parchment paper first so it didnt' transfer as good, but i was able to cover my mistakes up for the most part. after having 3 cakes to make this weekend and being bummed on my party turnout i didn't get the pics posted yet, but when i do, i will post them in this forum as well. thanx for all your help everyone! 
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