Nigredo is an additional, or secondary substance, which is present in some alchemical ingredients in addition to the primary substance. All alchemical ingredients contain one of six basic substances: aether, hydragenum, quebrith, rebis, vermilion and vitriol. There are also three additional substances: albedo, nigredo and rubedo. Any given ingredient may contain only a single basic substance and potentially one additional, or secondary substance.
Nigredo potions: If all ingredients used to create a given potion contain nigredo as an additional substance, the resulting potion will positively affect Geralt's coordination and focus, increasing his chances of hitting opponents and giving him a + 20% damage advantage for 4 hours.