You'll also need a large canning pot, and 2 large cooking pots-- stainless steel preferred. One pot for boiling the clean jars and lids and the other pot for the jam.
What you'll need for the jam: Sugar- lots of it! Lemon juice, blackberries and fruit pectin.
Take a colander and set it on a large measuring cup (mine is an 8 cup size) and then put the cheesecloth or flour sack towel on top. Place a layer of berries in the towel and smash with the masher.
When berries look like this, you are ready to SQUEEEEZE and say hello to your Popeye forearms!
Using the ladle (picture isn't the best, sorry), fill the jar almost to the top. Directions say, "Leave 1/4 inch head space." That just means almost to the top and leave a little wiggle room! After jar is filled, wipe the rim with a damp towel and retrieve a hot lid from the same pot you had the jars in. Wipe dry and place on jar, then tighten band. Use towel to hold jar while you tighten the lid.
Then take your jar tongs and carefully place into the hot water canning pot and make sure water covers the top of the jar by at least 2 inches. don't forget the water level will rise as you add more jars. Repeat until all the jam is in the jars and you have the canner filled. If you have some jam left and not enough to fill a jar, you can refrigerate and eat for breakfast the next morning.
Cover the canning pot with lid and return to a boil. When it starts boiling, then you can set your timer and boil for 10 minutes. After 10 minutes, use your jar tongs and carefully set on a towel. Cover all the jars with another towel to keep the jars from cooling too quickly. You'll hear the lids "popping".
Since I do my canning at night (so the kids don't bother me and it's cooler at night and I can sleep off the hot kitchen) by morning, the jars are cool enough to handle. Still a little warm and the jam isn't completely set yet. When it is completely cool, the jam in the jar should be set and you can store in a cool dry space for up to a year. If it lasts that long!
There you have it! Jam!! Or jelly if you prefer.. whatever.. it's yummy on toast, biscuits, desserts, fingers. Enjoy!