Place the 4 half-cup canning jars in a large pot with a trivet in the bottom. Cover with water so that the water comes 1 inch above the tops of the jars. Allow another inch of space above the water to allow for bubbling water. Place over high heat and bring to a boil. Sterilize the jars by boiling gently for 10 minutes. Turn off the heat and set aside until ready to fill the jars.

Rinse the 5 cups blackberries under cold water and drain in a colander. Place in a large bowl and mash with a potato masher.

Put a colander lined with a damp pressing cloth over a large pot. Place the mashed berries in the pressing cloth and let stand for about 5 minutes. The juice from the berries will drain into the pot below the colander. You may want to wear kitchen gloves or latex gloves for the next step to help keep your hands from becoming too discolored.

Raise the four corners of the cloth over the berries and twist close. Twist and squeeze the cloth tightly to extract as much juice as possible from the blackberries. All of the juice will be collected in the pot. You should have 1-1/3 cups of blackberry juice when done.

Place the juice in a 2-quart saucepan. Add 2 Tablespoons of Original Sure-Jell Powdered Fruit Pectin (1/2 of the package).

Place the saucepan over medium-high heat. Stir the juice until the pectin is dissolved and the juice begins to bubble up.

Quickly add the 1-1/3 cups sugar and stir thoroughly until the sugar is dissolved.

Bring to a full rolling boil and boil hard for 1 minute. Watch closely to avoid boiling over.

Remove from heat, skim foam, pour into hot, sterilized jars, and seal.

Process in a boiling water bath for 10 minutes. Remove jars from pot and place on a clean towel to cool.