I've been making Damson Jam. I'm sharing the method I use to make my jam, I've used this method for about 4 years now and it usually works very well.
Recipe from Delia Smith.
1.3 kg fruit to 1kg of preserving sugar.
Pick out any stalks - there weren't many as weed done most of that when we froze the fruit back in the summer.
Simmer the fruit in 15fl oz of water till soft.
At this point I de-stone the jam. My hubby likes the stones left in, but I don't. So we compromise and take out most, leaving a few in and a few whole fruit. this can take quite some time!
While I'm doing this the oven goes on at 180. and the sugar goes in a heat proof bowl to warm.
When done - fruit and sugar in the pan, stir lightly and leave on a low heat until the sugar has dissolved.
Then boil rapidly for 10 minutes. turn off the heat and check for set. put a little on a cold plate and allow to cool, if it wrinkles when pushed with your finger it's done. If not, boil for another 5 mins and test again. do this until the wrinkle check works (usually takes 15 mins boiling for me.)
Let settle for a few minutes and then pour into warmed, sterilised jars - put on lid and allow to cool completely.
store in fridge once opened - makes a great gift.