Thanks so much! To get the line quality I’m looking for I use a tool called a slip trailer. It’s a small bottle with a needle connected to it-that I can push underglaze through. I place the pot on a lazy susan so that I can spin the piece at whatever speed I need to get the design I have in mind. I have a few images of using one while decorating mugs. Check them out here: http://www.facebook.com/album.php?id=732706472&aid=284359
Thanks for asking!