| | Re: Bottle cap images and water proofing.
I have not personal used Mod podge for bottle caps. I have used an acrylic spray sealer that works well though. You can buy it at any craft store, usually in their framing dept. You spray it on lightly and let it dry and then do a second coat. I usually wait a couple of hours after printing images before sealing them, so that the ink has a chance to really dry.
Also, you can use resin instead of stickers for a truly waterproof seal. Resin will seal the whole cap shut so not water can get in. A sticker cannot do that and water will still get in if the cap is out in the rain or goes in a pool.