I have a can of Interlux Schooner varnish about 2/3's full. I make it a habit to spray some nitrogen into a paint/varnish cab before sealing it and that usually keeps a skin from forming on top so the next time I open it all it needs is to be stirred. Anyhow, this can of varnish. I poured it through a filter made for that purpose and found a "blob" of gelled varnish remaining in the filter. I've tried to mix it and it doesn't seem to want to mix. Should I just throw the gelled part out or the whole can or keep mixing? I hate to throw it away if it's usuable.
Personally, since varnish is near the end of the finish on bright work I would discard it and get a new can. . . However. . . If it is less than three years old, looks right and smells right you could do a dry test to determine if it is okay to use.
Spread a little on a piece of glass tilt it at a 45 degree angle and let it dry overnight. If it dries hard overnight on the glass you are good to go. I usually thin my first few coats by 15 to 20 percent and mid coats at around 10 percent before I go for a slightly thicker finish coats that gets buffed. If it passes the dry test and looks good I think you would be fine to thin it an use it.
JP