Alabaster
Looks like polished marble, is chemically nothing like it, and dissolves in water. The one surface where blotting a fresh spill is the error.
What not to do
Unsafe
Do not do this. The risk is established, and it is described below.
The identification is the hazard. Alabaster is gypsum and readily water soluble; marble is calcite and is not. They are routinely confused, and both are sold as onyx.
Evidence
Supported
Sources
Conserve O Gram 15/1: Care of Alabaster
National Park Service, US Department of the Interior, 2000 · Government or regulator
Relied on for: That alabaster is the fine-grained form of gypsum, that it is readily water soluble while marble is not, and that moisture contact of any kind is to be avoided. (states this directly)
Detergent is unsafe on Alabaster
Unsafe
Do not do this. The risk is established, and it is described below.
Evidence
Supported
Sources
Conserve O Gram 15/1: Care of Alabaster
National Park Service, US Department of the Interior, 2000 · Government or regulator
Relied on for: That unless a protective wax coating is certain, the reader should resist the temptation to wipe or remove stains by rubbing with detergent solutions. (states this directly)
In detail
Alabaster is the fine-grained form of GYPSUM — calcium sulfate — and the confusion with marble is the hazard. Marble is mainly calcite, calcium carbonate; the conservation guidance states the practical difference in one line: alabaster is readily water soluble, while marble is not. It is softer too, scratchable with a fingernail, and it takes a translucent polish that makes it look deceptively hard and glass-like. Objects sold as onyx are frequently one of the three. The guidance's assessment is that more damage has probably been done to alabaster by well-meaning cleaning than by anything else, and its method is nearly all refusal: keep loose dust off, because dust attracts moisture to the surface; use a soft bristle brush rather than a cloth, because a cloth builds static that attracts soiling; tape the brush ferrule so the metal cannot scratch. Anything beyond dry brushing goes to a conservator. The prohibition that matters most inverts the standing advice for a spill — do not rub stains with detergent solutions, and EVEN BLOTTING A FRESH SPILL CAN DRIVE IT IN AND MAKE IT PERMANENT. Where possible the stain is left to dry. Handling is gloved: finger oils penetrate and stain.
Properties
Sensitivity
- Acids
- Sensitive
- Alkalis
- Not known
- Chlorine bleach
- Not known
- Abrasion
- Sensitive
- Porous
- Sensitive
“Not known” means nobody has established this, not that the material is unaffected.
What works
Dry soil removal is safe on, in specific conditions, Alabaster
Safe only in specific conditions
This is only appropriate within specific limits, and nothing is established outside them.
Only within these limits:
- A soft bristle brush, NOT a cloth — a cloth builds static that attracts more soiling
- Masking tape wrapped around the brush ferrule so the metal cannot scratch
- Anything beyond simple dry brushing goes to a conservator
This is the whole of the permitted method. The source's own assessment is that more damage has probably been done to alabaster by well-meaning cleaning than by anything else.
Precautions
- Wear gloves
- Consider professional help
Evidence
Supported
Sources
Conserve O Gram 15/1: Care of Alabaster
National Park Service, US Department of the Interior, 2000 · Government or regulator
Relied on for: That a soft bristle brush with masking tape around the ferrule is directed instead of a cloth, and that if anything more than simple dry brushing is required a conservator should be consulted. (states this directly)
Why
- Alabaster is explained by Porous and non-porous surfaces
Related
- Alabaster is commonly affected by Dust
- Alabaster is commonly affected by Oil and grease on textile
Sources for this page
Sources
Conserve O Gram 15/1: Care of Alabaster
National Park Service, US Department of the Interior, 2000 · Government or regulator
Relied on for: That alabaster is the fine-grained form of gypsum while marble is mainly calcite, that alabaster is readily water soluble while marble is not, that it is softer and scratchable with a fingernail, that a soft bristle brush with a taped ferrule is directed rather than a cloth, and that rubbing with detergent solutions and even blotting fresh spills can make a stain permanent. (states this directly)