soapformulator
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Ingredients

Every ingredient a recipe here uses has a page: what it is, how it behaves, how to handle it, and where each fact comes from.

Oils & butters 207Saponification values, fatty acids and soap qualities for every oil and butter, each from a named source.
Additives 138Clays, milks, colourants, exfoliants and the rest: what each does, how much, and when it goes in.
Essential oils 53Each oil's IFRA maximum for soap, its allergens and how it behaves in a bar.

Lye and water

Sodium hydroxideSodium hydroxide is the strong alkali that turns oils and fats into bar soap and glycerin. Weighed to a calculated recipe it is used up in the reaction, but until then it is corrosive to skin and eyes, and it has to be bought, handled, stored and disposed of with care.
Potassium hydroxidePotassium hydroxide is the alkali for liquid, soft and cream soaps, and for the potassium share of a dual-lye recipe. It is sold as flakes that are usually about 90 % pure, so its purity has to be set in the calculator, and it is every bit as corrosive as sodium hydroxide.
Distilled waterDistilled or deionised water is water with its dissolved minerals taken out, used to dissolve the lye and to dilute liquid soap. In a bar recipe the minerals in tap water cost very little soap, but they cloud liquid and transparent soap and can bring the trace metals that speed rancid orange spots.

Helpers some methods use