If you have raisins or currants you can hydrate them in a sauce pan with some liquid and make a raisin puree.

cranberry jelly could work well.....

The idea of the balsamic plus honey is very helpful, though. Gotta love foodpickle!! ;o)

Thanks so much! I have a lovely, rather tart raspberry jam that I'll strain. Then I'll put in my calendar a reminder, during the month that they are in season (once I nail that down . . . . I think it's late summer here), to find some red currants and to make a small batch of jelly. I also have some tart quince juice in my freezer, which now seems destined to be the subject of a project before too long, as well. Thanks again. ;o)

don't over complicate it.I think verdigris solution sounds very appropriate. And I have used grape on many occasion, surprisingly currant jelly is not as easy to find as it once was
( at least that's the case here in Grand Junction, CO. )

I would suggest move any other berry jelly would work. If no jelly available, how about 1/2 tsp of balsamic vinegar mixed with a 1/2 tsp of sugar or honey?

Do you have any kind of grape or tart blackberry jelly? I think the point of the currant jelly is to add not just sweetness but tartness, so I'd aim for a jelly that emphasizes the latter.