Soap = fat + lye (caustic soda). Chemical reaction (saponification) turns them into soap + glycerin.
Ingredients
Fat: lard — cheap, from the farm. Olive oil — gentler. Coconut — lathers better. Best soap: mix 40% lard + 30% olive + 30% coconut. Lye (NaOH): bought at hardware store. Used to make from wood ash (ash + water → potassium lye).
Process
Dissolve lye in water (careful — exothermic, 80°C). Cool to 40°C. Melt fat to 40°C. Combine. Stir 20-40 minutes until 'trace' (thickens like pudding). Add scent (lavender, mint, oatmeal). Pour into mold. After 24-48 hours unmold, cut. Cure 4-6 weeks.
Safety
Lye is dangerous. Gloves, goggles, ventilation. Children — far away. Finished soap is safe (lye fully reacted).
Economics
10 kg fat + lye = 50 bars. Cost: $0.30-0.50 per bar. Market price: $3-6. Scented handmade soap — $5-10. Margin 80-90%.