Damage versus soiling
Some marks are something added, and some are something gone. Only the first kind can be cleaned, and telling them apart is the decision that comes before choosing any product.
In detail
A reader looking at a mark almost always assumes it is soil — a substance resting on or absorbed into the surface, which the right product will lift off. A large minority of marks are the opposite: the surface itself is missing or altered, and what looks like a dark patch is a change in how light meets a damaged area. The distinction decides everything after it. Soil responds to solvency, surfactancy, dwell time and mechanical action. Missing material responds to none of them, and every one of those levers applied harder makes it worse, because the only thing left to act on is the surrounding intact surface. This catalogue already held the pattern without naming it. Acid etching on marble is lost polish, not a stain. Heat tint on stainless is an altered oxide layer. Polishing removes metal. Grazed wool and exit holes in timber are material an insect has eaten. The test is usually about the surrounding surface rather than the mark, and raking light is the cheapest instrument for it: a stain leaves the specular highlight running smoothly over it, and damage breaks it. Where the answer is damage, cleaning is the wrong tool entirely.
Why
- Frass and pest residue is explained by Damage versus soiling
- Polished marble is explained by Damage versus soiling
- Ivory is explained by Damage versus soiling
The yellowing is the material, not something on it — which is why every attempt to clean it off fails.
- Fingerprint-resistant stainless steel is explained by Damage versus soiling
There is no sacrificial thickness to polish into. Taking the coating off is not cleaning.
- Cellulose nitrate is explained by Damage versus soiling
- Cellulose acetate is explained by Damage versus soiling
- Casein plastic is explained by Damage versus soiling
- Phenolic plastic is explained by Damage versus soiling
- Polyurethane foam is explained by Damage versus soiling
- Sticky plastic is explained by Damage versus soiling
- Oven door seal is explained by Damage versus soiling
- Phenolic yellowing is explained by Damage versus soiling
Sources for this page
Sources
Conserve O Gram 3/11: Identifying Museum Insect Pest Damage
National Park Service, US Department of the Interior, 2008 · Government or regulator
Relied on for: That grazed surfaces, chewing marks, exit holes and hair or fur loss are the visible evidence of pests, and that these signs rather than the animal are what is detected first. (states this directly)
Verification: a person has read the passage relied on.
Read on — 'Evidence of Pest Activity', 'Textile Pests', 'Clothes Moths' and 'Wood Pests'. Supports the claim as stated. Opens a class of question the catalogue could not previously take: whether the mark in front of the reader is a cleaning problem at all, or material that has already gone.
Conserve O Gram 15/1: Care of Alabaster
National Park Service, US Department of the Interior, 2000 · Government or regulator
Relied on for: That more damage has probably been done by well-meaning attempts at cleaning than by anything else, and that rubbing a stain can drive it in permanently. (background and mechanism only)
Verification: a person has read the passage relied on.
Read on — 'What is Alabaster?', 'Deterioration and Damage', and 'Care of Alabaster'. Supports the claim as stated. Adds alabaster as a material distinct from marble, and records the catalogue's first case where blotting — its standard first move on a fresh spill — is the specific error.
Last reviewed by a person on .