Pectin is the plant fibre that makes jam gel. Apples, citrus peel and quinces are rich in it; figs are not. Left to themselves, figs and sugar cook into a thick, spoonable preserve rather than a firm, sliceable jelly.
Without added pectin
This is how we make ours. The jam is cooked until enough water has evaporated for it to hold a soft set. It takes longer, the yield is a little lower, and the flavour is more concentrated. The texture is closer to a fruit spread than a jelly.
With added pectin
Commercial pectin, either powdered or liquid, gives a firmer, glossier set with a shorter cooking time and brighter colour. Follow the pectin maker's instructions exactly: they are formulated around specific ratios of fruit, sugar and acid.
Natural pectin boosters
Lemon juice adds both acid and a little pectin from the fruit. Some cooks add a grated apple or a few pieces of quince, which raises the pectin without much change in flavour.
Whichever you choose, the lemon juice stays. Its role in acidity and safety is separate from the set. See Acidity.