The best time to cut cold process soap is when it is firm enough to hold its shape but still soft enough to cut without cracking — typically 24–48 hours after pouring. Press the soap gently with a gloved finger: it should feel like firm cheddar cheese.
If the soap is too soft (your finger leaves a deep dent), wait another 12–24 hours. If it is too hard (difficult to cut, crumbles at edges), you waited too long — next time, check earlier. Recipes high in hard oils (coconut, palm, shea) firm up faster than high olive oil recipes.
Cutting tools: a multi-bar soap cutter gives the most consistent results. A stainless steel bench scraper or a long, sharp non-serrated knife works well for beginners. Some makers use a miter box with evenly spaced slots for straight cuts with a pastry scraper.
Technique: mark your desired bar width on the loaf with a ruler. Cut in one smooth, firm motion — do not saw back and forth. Wipe the blade between cuts for clean edges. For a rustic look, use a crinkle cutter which adds a wavy texture to bar surfaces.
After cutting, place bars on a curing rack with the cut sides exposed to air. The bars will be slightly soft at this stage — handle them carefully to avoid dents and fingerprints. Wash your hands thoroughly after handling freshly cut soap.