Wash jars, lids, and rings in hot soapy water. Put jars in the waterbath canner, and cover completely with water. Bring to a simmer (don’t need to boil). In a small saucepan, add lids and bring to a simmer. You don’t need to add the rings. It is important to keep jars and lids hot or your jam might not seal.
To make the jam:
Wash and prepare blackberries. Place blackberries in a deep bowl or pot and crush using a potato masher. Crush enough blackberries until you have 4 cups of crushed blackberries. In a six or eight quart saucepan, add crushed blackberries. Stir, or whisk in pectin until dissolved. Bring mixture to a full rolling boil (a boil that doesn’t stop bubbling when stirred) on high heat, stirring constantly. Stir sugar in quickly, all at once, and return to a full rolling boil and boil for one minute, stirring constantly. Remove from heat. Remove any foam that has settled on top of the hot mixture.
To process the jam:
Remove one jar at a time from the canner. Empty the water in the jar back into the canner. Fill jars within ¼ or an ⅛ of top. Wipe jar lids and threads. Center lid on jar, add ring, and screw tightly. Place all jars in canner. Add enough water to cover by at least one inch and increase heat to high. Once the water reaches a full boil, cover and boil for 10 minutes. Turn off heat and remove lid. Allow jars to rest for 5 minutes, then remove from pot. Let cool completely before storing, at least 24 hours.
Other things you'll need: 8 Ball 8-ounce jars with lids and rings, Waterbath canner (21½ quart with rack and cover), Jar funnel, jar lifter, and magnetic lid lifter