Amber Anti-Oxidation Coating

[NZ_Fossil_Collecta]

---topic closed by owner---

Edited May 23, 2014 by NZ_Fossil_Collecta

[painshill]

Only just spotted this.

Personally, I would be extremely reluctant to follow that advice. Everything I know about the chemistry of amber deterioration suggests it would be extremely unwise to apply any kind of coating in an attempt to exclude oxygen. Degradation is not just about oxygen availability. Yes, it’s a good idea to limit oxygen availability but the generally accepted advice is to achieve that by the use of sealed containers and oxygen scavengers – not by applying any kind of coating which might initiate other unpredictable chemical effects.

Here’s a link to the Canadian National Park Service “Conserv-o-Gram” Identification and Care of Amber:

http://www.nps.gov/museum/publications/conserveogram/11-17.pdf

Expanding on that (sound) advice, from experimental tests with Baltic amber samples, it has been determined that the major pathways by which amber degrades are:

- acid hydrolysis of succinate ester into communol and succinic acid;

- saponification of succinate ester (in alkaline conditions);

- thermal-oxidation and photo-oxidation of terpenoids;

- depolymerisation of the chemical structure;

- decomposition of terpenoids with production of volatile organic acids.

Consequently:

- heat, UV radiation and also visible light can cause rapid degradation;

- oxidation of terpenoids, commencing at the surface, is the major cause of degradation, since oxygen is involved in the depolymerisation, breakdown of terminal unsaturated carbon-carbon bonds and formation of communic acid from communol;

- amber is sensitive to both high and low relative humidity;

- acidic and alkaline pH conditions can both cause chemical changes and surface deterioration.

The detailed chemistry may vary with ambers other than Baltic, but those are still the main pathways. Introducing any other chemicals to amber (especially organic chemicals) can have unpredictable consequences by initiating chemical changes which promote the deterioration. Surface effects can spread rapidly, exacerbated by any hairline cracks or crazing in the specimen which allow ingress below the surface. Turtle Wax car polish is a complex mixture of organic polymers including waxes, solvents, surfactants and other chemical additives.

The recommended storage conditions for limiting deterioration are therefore:

- room temperature – an ambient temperature no higher than 22 °C should avoid any promotion of degradation of amber. The lower limit temperature is recommended as 17 °C (Thickett et al., 1995). It is also important that the temperature remains stable, since fluctuating temperatures cause structural damage from expansion and contraction (Callister, 2002) and indirectly affect relative humidity;

- limited exposure to light – amber specimens should not be exposed to intense or direct light, whether artificial or natural;

- low oxygen concentrations – anoxic or at least hypoxic micro-atmospheres;

- mid-range relative humidity around 50% – neither a very low nor a very high relative humidity, both of which cause degradation (respectively, acidic vapours off-gassing and hydrolysis). Again, fluctuations are to be avoided to prevent shrinking and swelling oscillations (Williams et al., 1990);

- neutral pH – both acidic and alkaline pH conditions in humid environments cause degradation by hydrolysis. Alkaline pH seems to initiate worse visible effects from saponification but naturally-released organic acidic vapours also create acidic conditions in the presence of moisture, aggravating other chemical effects.

[Ref: Archaeological Baltic amber: Degradation Mechanisms and Conservation Measures - Gianluca Pastorelli 2009]

Later Addition: I forgot to add that using proprietary formulated branded products in these contexts also leaves you vulnerable. It only needs the marketing guys to decide it could be improved by being "pine-fragranced" or claim "new improved winter performance" and the formulation change could leave you in big trouble.

Edited May 21, 2014 by painshill

[NZ_Fossil_Collecta]

I don't know what to say... None of my specimens have any damage to them whatsoever and apparently it is used by many amber dealers. If there is a better household substance that I could use to protect amber, though, I would love to hear about it.

[painshill]

I'm not saying that I know it to be harmful, but it goes against all other advice I have ever seen (and against my intuition for the chemistry of what may happen)... that you should keep chemicals of any kind away from amber and focus on the physical conditions for its curation.

Museums use UV-filtered low intensity lights and sealed displays in conjunction with controlled temperature & humidity, oxygen-scavengers and pollution-scavengers (neither in contact with the specimens). I'm not aware of any museum using protective coatings or other directly-applied chemicals.

I don't see any reason to take a chance by ignoring that advice.

[painshill]

Some further comments on the “EDITS” above:

"APPARENTLY you are supposed to handle amber a lot as your skin oils coat it and help block oxygen."

Noooooo! As well as the oils from your skin, you may also transfer chemicals from your sweat, which is usually acidic and contains potentially harmful organic chemicals such as butyric acid and propionic acid. I would recommend minimal handling.

"… a 'frosty' condensation like effect will probably form on the surface of your amber. I don't see it as physically harmful, and you just need to give it a good wipe (again a microfiber cloth does best) when you need to look at it. I am pretty sure it is just the oxygen 'beading' on the surface."

No again! Frosty condensation would likely be the first indicator that chemical attack has begun. It has nothing to do with “oxygen beading on the surface” (???!!!) Wiping it off would be a good idea, but the kinds of processes we are talking about are progressive. It’s important to stop them initiating because it’s much more difficult to arrest them once they have started.

(my opinions)

[hammada]

Totally agree, bravo!