One of my children just asked me if ink is a חציצה [interposition] for netilas yadaim.
The Shulchan Aruch says that wet ink is not but dry ink is and must be removed. However, if the ink is not substantial then it is not a problem. That means that if one cannot peel the ink off with a nail then it has the status of חזותא בעלמא [mere appearance] and does not constitute a חציצה. Most of our inks are חזותא בעלמא and thus not a problem.
להצלחת גיטל פייגא בת ביילא בלומא בכל העניינים