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I don't harvest them from bushes in my garden - there are plants which are "natural soaps" in that they contain saponins (chemicals of course, like the rest of the plant); plants like Soapwort, which is still used to wash some old and delicate fabrics.
But a bar of soap can't be "natural" as it is formed by a chemical (re)action between lye and fats. Lye itself isn't natural either, the sodium hydroxide used in solid soaps is usually formed from brine by electrolysis and is often a by product from the manufacture of hydrochloric acid.
So don't let anyone tell you their soap is "natural".
Nor can it be "chemical-free" - think about it!
Everything is composed of chemicals, some are good and some are bad.