Dissolve the baking soda in about 2 quarts of cool water, and immerse the figs in the treated water in a large bowl. Gently stir to wash the figs, then drain off the water and rinse the figs thoroughly with fresh cool water. Place the figs into a large pot. Add 1 cup water, sugar, butter, vanilla extract, lemon, lemon juice, cinnamon, ginger, and cloves. Very gently stir the mixture to dissolve the sugar, keeping the figs intact as much as possible.
Bring the mixture to a boil over medium heat; reduce heat to a simmer, and cook until the figs are golden brown and coated in syrup, about 1 hour. Stir gently a couple of times to keep the figs from burning onto the bottom of the pot. Add a pinch of salt, if desired, to tame the sweetness.
Sterilize the jars and lids in boiling water for at least 5 minutes. Pack the figs into the hot, sterilized jars and top off with syrup, filling the jars to within 1/4 inch of the top. Run a knife or a thin spatula around the insides of the jars after they have been filled to remove any air bubbles. Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with lids, and screw on rings.
Place a rack in the bottom of a large stockpot and fill halfway with water. Bring to a boil over high heat, then carefully lower the jars into the pot using a holder. Leave a 2 inch space between the jars. Pour in more boiling water if necessary until the water level is at least 1 inch above the tops of the jars. Bring the water to a full boil, cover the pot, and process for 15 minutes.
Remove the jars from the stockpot and place onto a cloth-covered or wood surface, several inches apart, until cool. Once cool, press the top of each lid with a finger, ensuring that the seal is tight (lid does not move up or down at all). Store in a cool, dark area, and wait at least 2 days before opening.