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. Process in a boiling-water bath for 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 7 to 8 (1/2 pint) jars.