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Soap versus detergent

Everyday speech treats them as synonyms. A conservation instruction that permits one and prohibits the other in the same paragraph shows they are not.

In detail

Soap is made by reacting a fat or oil with an alkali; detergent is synthesised, and the family is subdivided by the charge the molecule carries — anionic, non-ionic, cationic. Both clean by surfactancy, which is why the words get used interchangeably, and there are surfaces where the difference decides the outcome. Federal conservation guidance for finished wood permits a weak solution of a MILD SOAP in warm water for stubborn dirt and then, in its own sentence, prohibits the other family outright: never use detergents, because they leave a film that is difficult to remove and which may permanently damage some finishes. It names acceptable soaps and excludes a dishwashing liquid by name, so it means the chemical class rather than 'anything gentle'. The mirror image appears in the same series: for outdoor bronze a NON-IONIC detergent is specifically directed, and the stated reason is the same property read the other way — non-ionic surfactants rinse off easily, which is what a porous masonry substrate requires. Neither family is better. What differs is what is left behind, and whether the surface underneath can tolerate it.

Why

Sources for this page

Sources

  1. Conserve O Gram 7/1: Cleaning Wood Furniture

    National Park Service, US Department of the Interior, 1993 · Government or regulator

    Relied on for: That a weak solution of a mild soap in warm water is permitted for stubborn dirt on clear-finished wood, and that detergents are never to be used because they leave a film that is difficult to remove and may permanently damage some finishes. (states this directly)

    Verification: a person has read the passage relied on.

    Read on — The whole leaflet: the clear-finished, painted, unfinished and wax-over-bare-wood sections, and the caution. Supports the claim as stated. Supplies the first fully-specified positive cleaning system in the catalogue for finished wood: gate, test, agent, escalation, rinse, dry and required aftercare. It also forces a distinction the catalogue models as two agents and had never used — soap is permitted here and detergent is prohibited.

  2. Conserve O Gram 10/5: Caring for Outdoor Bronze Plaques, Part II — Cleaning and Waxing

    National Park Service, US Department of the Interior · Government or regulator

    Relied on for: That a non-ionic detergent is directed for cleaning bronze, and that non-ionic detergents are low in toxicity and can be easily rinsed from surfaces. (states this directly)

    Verification: a person has read the passage relied on.

    Read on — 'Introduction to Cleaning and Waxing', 'Preparation', 'Cleaning' and 'Waxing'. Supports the claim as stated. Supplies a complete outdoor metal cleaning system with required aftercare, and one fact with much wider reach than its subject: distilled water is more aggressive than tap water and etches carbonate stone.

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