Thoroughly crush raspberries, one layer at a time. We actually sieved raspberries until we had 1 cup without seeds and then crushed enough with seeds to equal 1 1/2 cups. We wanted some seeds, just not a lot.
Finely chop unpeeled rhubarb.
In large mixing bowl stir together prepared fruit and sugar.
Let stand 10 minutes.
Add Certo Liquid Pectin and lemon juice. Stir 3 minutes.
Put into clean containers filling up to 1/4 inch from rim. Cover with lids. Leave at room temperature 24 hours or till set.
Notes" No-cook jam may be stored in the refrigerator for up to 3 weeks or can be kept in the freezer for 6-8 months.
Sterilized containers are not required for no-cook jams, they simply need to be washed in hot soapy water and rinsed before use. Plastic freezer containers, or glass jars with tight-fitting lids that are no larger than 2 cups can be used.