Wash the jars and screw bands in hot, soapy water, then rinse them off with warm water. Pour boiling water over the flat lids, cleaned jars, and cleaned bands, then allow them to soak for at least five minutes.  Note that you can also wash the jars in your dishwasher if your machine has a “sterilize” setting, but the lids and bands should still be washed by hand. You can prepare the jars after the jam is finished, but to improve efficiency and reduce the total amount of time, you may wish the sterilize the jars, lids, and bands before or while you work on preparing the jam. Fill a boiling water canner halfway with water. Set it on your stove and allow the water to reach a full boil. If you don't have an actual boiling water canner, you can use a large stockpot. Place a metal rack at the bottom of the stockpot before adding and boiling the water. This rack should prevent the glass canning jars from coming into direct contact with the heat source. Fill eight 8 half-pint (250 ml) jars with your plum jam, leaving 1/4 inch (1.25 ml) empty head space at the top of each jar.  After filling the jars, wipe away any spilled jam using a clean, damp towel, then secure the lids and screw bands over the top of each jar. Note that pint-sized (500-ml) jars may also be used, but you'll only need about four of them. Leave the same amount of headspace regardless of the jar size. The headspace prevents the jam from expanding and cracking the glass jars. Use jar tongs to lower the filled, sealed jars into the boiling water of the canner.  Keep at least 2 inches (5 cm) of space in between the jars to prevent them from hitting each other as they process. Note that there should be at least 1 to 2 inches (2.5 to 5 cm) of water covering the tops of the jars. If there isn't enough water in the canner, add more boiling water before you begin processing the jars. Cover the canner and process the jars of jam for 5 to 15 minutes, depending on your altitude. Keep the water boiling throughout this entire time.  For altitudes between 0 and 1000 ft (0 and 305 m), process the jars for 5 minutes. For altitudes between 1001 and 6000 ft (305 and 1830 m), process the jars for 10 minutes. For altitudes above 6000 feet (1.83 km), process the jars for 15 minutes. Also note that these processing times should remain the same for both half-pint (250-ml) and pint (500-ml) jars. Carefully remove the processed jars of jam from the hot water. Transfer them to a cloth-covered surface and allow them to cool to room temperature.  Make sure that the jars do not hit the canner or each other on the way out. The glass may break if this happens. It will usually take several hours for the jars to completely cool. You may even need to wait overnight depending on when you started the process. Once the jars are completely cool, test the seal by pressing down on the button at the center of each lid. That button should not move up and down when pressed.  Test the seal on each jar. Do not assume that all seals are fine just because the first one or two seem secure. If the jar has not been sealed correctly, transfer it to the refrigerator and use the jam within a few weeks. If you do not want to use any unsealed jam immediately, you could also try reheating the jam, placing it a new jar with a new lid, and processing it again. Label the jars with their contents and the current date, then store the finished jam in a cool, dry, and dark place for 6 to 8 months. After opening a jar of plum jam, store it in your refrigerator and use it within three weeks.
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One-sentence summary -- Sterilize the jars and lids. Boil water in a hot water canner. Meanwhile, ladle the jam into your prepared jars. Carefully place the jars in the boiling water. Process 5 to 15 minutes. Let the jars cool. Test the seal. Store the finished jam.


The Tunisian double crochet starts after you have completed a preparation row using the Tunisian simple stitch.  You can also work the Tunisian double crochet into larger piece of Tunisian simple stitches. The preparation row is a minimum start, but not a maximum start. Make sure that you have completed a reverse pass before you start the Tunisian double crochet. There should only be one loop on your hook when you start. Work two standard chain stitches from the loop on your hook. These chain stitches will help accommodate the eventual height of your Tunisian double crochet row. Yarn over the hook once, then insert it into the second vertical bar. Yarn over again, then draw this yarn-over back through to the front of your work, creating a loop. Yarn over once more, then draw your last yarn-over through two loops on your hook.  Note that the first vertical bar should be skipped over, as done with the simple stitch. Leave the final loop of the stitch on your hook. There should already be one loop on your hook from before that, however, giving you a total of two loops on the hook at the end of this first double crochet. The difference between the Tunisian simple stitch and the Tunisian double crochet lies entirely in this forward pass part of the process. Repeat the previous step, working into each vertical stitch of the previous until you reach the end of that previous row.  For each stitch, yarn over the hook once, insert it into the next vertical bar, and yarn over again. Draw the yarn-over back through to the front, yarn over again, and draw this last yarn-over through two loops on your hook. For the last vertical bar, insert the hook into the horizontal stitch lying to the right of the vertical bar as well as the vertical bar itself. When pulling a loop back through to the front of the work, make sure that you pull it through both bars again. This adds stability to the edge of the work. When you reach the end of your forward pass row, you should have 10 loops on your hook, or the number of stitches you started with in your foundation chain. Yarn over the tip of the hook and draw that yarn-over through one loop previously on your hook. Note that the reverse pass for the Tunisian double crochet is the exact same as the reverse pass for the Tunisian simple stitch. Yarn over the hook, then draw that yarn over through two loops on the hook.  You should be left with one less loop on your hook at the end of this step. Repeat this step until only one loop remains on the hook. Alternate back and forth between the forward pass and reverse pass until you reach the end of your Tunisian double crochet section or the end of your work as a whole.  Always end with the conclusion of a reverse pass. Skip down to the section on "Finishing the Work" if you are ready to tie off the work at the completion of this step.
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One-sentence summary --
Work a preparation row using the Tunisian simple stitch. Chain two. Forward pass into the second vertical bar. Work across the rest of the row. Reverse pass through one stitch. Reverse pass through the rest of the row as usual. Repeat as needed.