The message
from "BAC" contains these words:

No doubt jam makers will be able to supply recipes and tips.

With Japanese quinces you should have no problem with it setting.
Problems with bent spoons, maybe.

Don't anyone suggest citric acid - -nearly all commercial jam has citric
acid in it and you can taste it. I suppose it allows the makers to add
more water....

When I want marmalade I'll buy marmalade.

Pectin's another matter. That doesn't alter the flavour significantly.

--
Rusty Hinge
No m'lud, it wasn't a sneg. My joints creak.