Rinse 4 cups blackberries and remove stems
Mash the berries lightly in a large pot
Add 4 cups sugar
Add 2 tablespoons lemon juice
Stir and let sit for 10 to 15 minutes
Bring the mixture to a boil over medium-high heat
Stir constantly until the sugar dissolves
Reduce heat and simmer for 15 to 20 minutes
Skim off any foam from the surface
Test the preserves for thickness
Remove from heat when desired consistency is reached
Pour into sterilized jars
Seal the jars while hot
Let cool completely before storing
Refrigerate after opening