There are all sorts of ways that will work. This works for me:
Cast the tube in whitish opaque resin.
Turn to .02 less than finished size (tube will not be visible unless you made the white resin too transparent).
Apply label (I use clear waterslide labels with the white resin supplying "white" where needed, since printers don't print white).
Allow label to dry (for waterslide I let it sit overnight and then give it an hour in a warm toaster oven <150F)
Spray Krylon Crystal Clear Gloss coating from a can after the labelled blank has cooled.
Allow to dry overnight and then give it an hour in a warm toaster oven <150F). Allow it to cool.
Degass my resin with vacuum in it's mixing cup before pouring into the mold.
Pour the resin carefully to not introduce bubbles. DO NOT put the mold with the label / resin under vacuum. If you got bubbles in the resin while pouring, move them away from the blank with a toothpick or something.
That's it. You could probably drop some of my steps and have success, but this process always works for me. Short cutting the process would sometimes work, but sometimes not.
Here's an example of one of mine (using ivory background resin):
View in Gallery
Ed