Preventing Stain From Ink Under Wallpaper

Just above my finger, you can see a bit of a green line.  A previous installer must have used ink to mark his plumb line .  Problem with this is, as you can see, ink will work its way through many substances, including wallpaper , and leave a stain on the surface. 
In this case, I removed the old wallpaper and then skim-floated the wall to smooth it.  As you can see, the ink, which is decades old (original wallpaper dates to the early ‘90’s ) is still active and has bled through the smoothing compound / joint compound .  If I were to prime and then hang wallpaper over this, it would work its way through both my primer and the homeowner’s new wallpaper.
So I’m sealing it off.  Above the green line you can see a strip of stain blocker brushed (actually daubed on with my finger) over the stain. 

I like to use KILZ Original oil-based stain blocker.  BIN shellac-based is another good product.  Don’t believe the claims on cans of water-based alternatives – nothing works as well to block stains as KILZ or BIN.  The fumes can be strong, and KILZ can make you high, so ventilate the room and/or wear a respirator when you apply this stuff.
Other substances / stains that can bleed through paint and wallpaper are tobacco , water , rust , marker , crayon , blood , oil , grease , food , hand prints , cosmetics , hair products , and so forth. 

Tags: '90's, bin, bled through, fumes, hang, ink, installer, joint compound, KILZ, oil based, plumb line, prime, primer, respirator, shellac based, skim-floated, smooth, smoothing compound, stain, stain blocker, wall, wallpaper, work its way through