Wash, stem, drain, and crush berries. Drip through jelly bag or
cheesecloth-lined sieve to equal 3 1/2 cups blackberry juice. Add dry pectin and sugar. Stirring to mix well. Stirring constantly, bring to a rolling boil and boil 1 minute (a rolling boil can
not be stirred down). Remove jelly from heat.
Skim off bubbles. Ladle jelly into hot, sterilized containers, one at a time. Fill to within 1/8 inch of top if using self-sealing lids. Fill to within 1/2 inch of top is sealing with paraffin. Wipe rim of jar or glass with a clean damp cloth.
If using self-sealing lid: Place hot lid on jar. Tighten screw band firmly. Invert jar 30 seconds. Stand upright to cool. Or, process in a boiling-water bath, 5 minutes.
If sealing with paraffin: Spoon a 1/8-inch layer of melted paraffin over jelly, covering completely. Cool 5 to 10 minutes until paraffin hardens. Place another spoonful of melted paraffin top. Till and turn container so paraffin runs 1/4 inch of more up side. Cool 24 hours. Cover with lid or foil.
Yields 5 to 6 (6-ounce) jars.