jam help please

buxtonrabbitgreen

I have a load of frozen fruit from last summer/autumn and I want to make jam as my stocks from fresh are finished. I have blackberries damsons cherries and raspberries. Impossible to know the weitght as they are frozen. Can I make mixed fruit jam? Which would go best together, or all of them?
Looking at some recipies on the net it seems I will need apples and or lemon to go with the blackberries.
No where in the villiage sells pectin or jam sugar so I will have to improvise.
I did make cherry jam with frozen cherries a couple of months ago using the fresh jam recipie but it didn't set despite extra sugar and boiling. It made a lovely coulis though and kept well in the fridge for cheesecake topping.
I am just off to buy lemons and sugar so any advice when I get back would be welcome. Thanks.

Seakay

Fesh lemon juice should provide enough pectin for you frozen fruit jams. Freezing seems to make pectin deteriorate, so even the damsons (usually great setters) will need some.
I would allow 2lb sugar and the juice of 2 lemons to every 2lb of fruit to be on the safe side.
I think that damsons would be best on there own as they have such a strong flavour, but any of the others would be great mixed or alone.
Ordainary sugar is fine for jam making.