What is this liquid called in my India ink? I recently discovered that India ink/China ink dries up in the bottle after many years, leaving an almost clear liquid on top (most likely shellac). This liquid works a wonder as glazing liquid. 

I searched for glazing liquids for paintings, but all I found are gloss mediums to use with the paint to increase flow and give a glossy finish.
But I'm looking for a simple thing which will allow a subtle to medium glaze after being applied on top of the finished painting, like a polishing liquid. Not varnish.

What should I look for precisely? Are there such things?
India ink has only three ingredients: lampblack, water and gelatin or shellac as a binder(in fact, traditional India ink doesn't even contain this), with shellac being much more common. As you've guessed, this means that the clear liquid on top is probably a mixture of shellac and water.

Shellac can be found easily online (if you can't find it in person) either as flakes or a liquid.