Whitening yellowed ivory

Does it work?

Does not work

Refuted on the premise rather than on efficacy. A national conservation institute addresses this exact question and instructs against it, and names two of the circulating methods as almost certainly seriously damaging. Sprint 29 recorded three popular methods as rejected observations with the method explicitly disbelieved; this is the authority that closes them.

This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.

Where not to use it

The proposed mechanism

The explanation below is what is offered for this technique. CleaningHQ has not found evidence establishing that this is what actually happens, and says so rather than presenting a plausible story as a finding.

That the yellow is accumulated surface soil or an oxidised film which a mild abrasive, a bleach or ultraviolet light can lift or decolourise. The conservation position denies the premise rather than the chemistry: the colour is the material's own ageing through its depth, not a layer sitting on it, so there is no film to remove and anything that lightens the surface has removed surface.

Background

Toothpaste, milk, lemon juice, bicarbonate paste, a spell in direct sunlight, peroxide, fine sandpaper. The methods differ; the assumption behind all of them is the same, and it is the part that is wrong. THE YELLOW IS NOT A STAIN. A national conservation institute states that ivory and bone develop a brownish-yellow patina through natural ageing, that there is rarely any aesthetic reason to whiten the object, and that NO ATTEMPT SHOULD BE MADE to remove it. On the specific techniques it is blunter: sanding or bleaching will almost certainly cause serious damage. So this is not a technique that works badly. It is aimed at something that is not dirt, on a porous material where every removal route takes surface with it. Abrasives cut dentine away and it does not grow back. Bleaches attack the organic component that holds the material together. Some ivories carry a patina applied deliberately as a surface stain, so whitening removes the finish the object was made with. There is a real answer underneath the refusal and it is small: dust it, and if it needs more, use the swab method the same authority permits. What the reader wanted is not available at any level of skill.

What it does not do

• The premise is wrong before the method is: the yellowing is ageing of the material, not soil on it
• Sanding and bleaching are named by the conservation authority as almost certain to cause serious damage
• Ivory is porous and abrasion removes dentine irreversibly
• Some ivories carry a deliberately applied stained patina, so whitening destroys the intended finish
• A reader may not be able to tell ivory from the cellulose-nitrate imitation before starting

What to use instead

• Ivory — The yellowing everyone wants removed is the material ageing, and the conservation authority's instruction is to leave it. Almost every circulating method attacks a patina rather than a stain.
• Dry soil removal — Taking the loose material away before any liquid touches it. Skipped almost universally, and it is the step that decides whether the rest works.