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CONSERVATION OF AMBER
and its inclusions
Deterioration
often manifest as:
Crazing
XThe formation of a network of cracks over the surface of an amber piece. If left untreated, these fine cracks can lead not only to superficial flaking, but also infiltration of the specimen over time, erupting along internal fractures, even directly compromising inclusions.
Colour changes
XColour changes (‘darkening’, ‘yellowing’ or ‘reddening’) of amber – due in part to prolonged heat exposure – is especially prevalent in some older collections. Such darkening will eventually obscure any inclusions, and is only reversible in specific cases by trimming/grinding away some of the amber.
Breaking
XIn the worst cases, breakage of the amber piece occurs, along with destruction of its inclusions.
Spalling
XIndications that a specimen has internal damage include spalling, exfoliation and powder, as well as the formation of a desiccated rind or crust on the amber surface. Networks of minute cracks may also develop inside an amber piece close to the surface of an inclusion.
Pyrite disease
XPyrite disease has never previously been discussed as a potential hazard for amber collections. However, in and around some amber specimens, we observed a greyish powder with yellow crystals commonly associated with pyrite disease, as well as the formation of some dark-to-grey crystals in contact with amber inclusions
Causes:
UV-light and Daylight
X Prolonged exposure to UV-light (100–400 nm) and visible daylight (390–750 nm), especially behind window glass without UV blocking filters will cause severe damage to amber, since it induces the oxidation of the molecular structure of the amber. Play with the window shade to control the light coming in. When it turns green it means that the light is adequate to preserve the amber piece.
Temperature
XElevated temperature and fluctuations in it including freezing, in conjunction with changes in oxygen level, has been shown to achieve specific colour changes in amber. Click on the buttons and find out which is the optimal temperature to preserve the amber piece when the thermometer goes green.
Relative Humidity (RH)
XLevels or changes in RH can cause or contribute to deterioration in fossil resins, but deleterious effects vary between different ambers. An increased RH in combination with thermal stress can accelerate amber degradation and promote pyrite disease. Find out which is the ideal RH when the hygrometer goes green.
Oxidation
XOxidation is the most problematic hazard for amber since it is intrinsically linked to O2 and other environmental factors, particularly temperature, light and airborne pollutants, all of which contribute to the oxidation process. This process can cause depolymerisation and also lead to colour change (yellowing/darkening) as well as the eventual fragmentation of the specimen inside amber. You cannot control the oxidation process, that's why the O2 icon changes itself. Look at it, the more temperature and humidity, the more oxidation there will be.
Now play with the other icons and see what happens.
Hazards:
X
Biocide vapours of naphthalene, paradichlorobenzene and camphor can lead to a partial dissolution of the amber.
Substances like ammonia, formic or acetic acid and hydrogen peroxide can significantly damage amber specimens, causing darkening, ‘crizzling’ and exfoliation.
Acidic and alkaline environments cause chemical changes in amber specimens, specifically alkaline hydrolysis (saponification) or acidic hydrolysis of the succinate ester, resulting in the formation of communol and communic acids.
Storage of amber samples in rooms with a high RH may support growth of fungal mycelia and bacteria on amber surfaces, and such growth may even extend into fissures and cavities within the amber. According to our observations, such microbes are not able to penetrate into the solid resin. Thus, there is no immediate risk to the fossil specimens enclosed in the amber. In any case, amber specimens should not be treated with disinfecting agents to stop or prevent microbial growth, since these agents will likely penetrate the amber and its inclusions and affect their physical and optical properties.
Chemicals, Cleaning Agents and Pollutants
Recommendations
Storage
XStore in a climate-monitored environment or in climate chambers.
Limited UV-light/daylight exposure.
Temperature at or just above 18°C.
Stable Relative Humidity of 50 %.
Use form-fitted plastic containers.
Use acid/alkaline-free soft paper or Plastazote foam to envelope the amber.
No storage in alcohol, water, solvents or oils.
Epoxy Embedding
X
Before Start
The preservation method currently favoured by researchers is to embed amber in a high-grade ‘glass conservation’ epoxy (e.g. EpoTek 301-2), which can in turn be trimmed and polished to conform to the shape of each amber piece, while hermetically sealing it to create an anoxic environment.
Here are the preparation techniques and protocols for embedding amber in epoxy:
Before embedding
Wash crude amber pieces in water.
Select samples and screen these for inclusions.
Grind and polish amber surfaces.
Take images of prepared amber inclusions.
Prepare and label cups or silicon forms / moulds.
Mix a small amount of quick-setting epoxy.
Mix appropriate amounts of high grade epoxy resin and hardener (by weight ratio as indicated). Epo-Tek 301-2 (or similar) is recommended.
Embedding
Work in a well ventilated area.
Affix specimen to bottom of a mould,using quick-setting epoxy.
Pour mixed epoxy solution into the mould, so that the amber piece is fully immersed.
Move all the bubbles in the liquid mixture well away with a pin.
Make sure no bubbles lie directly on any amber surfaces.
Vacuum
Place the moulds or cups on the vacuum platform.
Apply a thin film of petroleum jelly to the rim of bell-jar.
Make sure that all air valves of the vacuum assembly / stage are closed.
Place the bell-jar onto the stage to enclose the moulds.
Engage vacuum pump or oven (vacuum pressure of 50 mbar is recommended).
Leave specimens under vacuum for approximately 5-10 minutes. Let vacuum subside gradually.
Carefully remove bell-jar (wipe off rim).
Move any remaining bubbles away from amber surfaces.
Set specimens aside in a safe place to cure for approximately three days.
Prepare specimens after curing of epoxy
Note location of inclusions in each embedded piece.
Trim specimens carefully.
Grind and Polish each specimen.
1
Before embedding
2
Embedding
3
Vacuum
4
After curing
Digitization and Research:
Take care while performing some processes
XImaging: use cold lights with long goosenecks; merge images of each focal plane to photomicrographic composites using stacking software; no immersion of amber in glycerol or oil.
Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are invasive methods that should only be used for specific research purposes.
For creating 3D visualizations of inclusions, use X-ray based methods, such as µCT1(Micro computed tomography) or SRµ-CT2(Synchrotron radiation micro-computed tomography). However, SRμ-CT2 causes brownish discoloration of the amber.
Sadowski, E.-M.*, Schmidt, A.R., Seyfullah, L.J., Solórzano-Kraemer, M.M., Neumann, C., Perrichot, V., Hamann, C., Milke, R., Nascimbene, P.C.* (2021). Conservation, preparation and imaging of diverse ambers and their inclusions. Earth-Science Reviews. https://doi.org/10.1016/j.earscirev.2021.103653
