Posts Tagged ‘deterioration’

Under Construction, August 2011

1. BACKGROUND

Shells can refer to various types of hard protective coverings composed primarily of calcium carbonate and comprise the exoskeletons of invertebrates, the outer layer of an egg or other similar specimens commonly found in natural history collections.

2. POSSIBLE CAUSES

The most common cause of white stuff on shell is Byne’s Disease. Is it contagious?? No, Byne’s is not a transmissible or infectious disease and cannot be spread to you or throughout your collection. What it can do is alert you to improper storage conditions.

Byne’s is a chemical reaction that causes the physical breakdown of calcareous (containing calcium carbonate) materials. The phenomenon is named after Loftus St. George Byne, a 19th century British amateur naturalist who described the finding of this condition in shell collections. He mistakenly assumed the condition was caused by some type of bacteria. Subsequent research in the field revealed that the condition was actually due to chemical reactions taking place at the shell surface. Nonetheless, the term Byne’s “disease” stuck and is still in use.

When the calcium carbonate in shells comes into contact with acidic vapors, salts can crystalize on or erupt through the surface of the shell. Acidic vapors can off-gas from certain storage materials – particularly wood-based and certain plastic products. These kinds of materials can produce acetic acid and formic acid gases, which are then dissolved in atmospheric water and combine with calcium carbonate to form calcium acetate and calcium formate salts. Higher humidity creates more atmospheric water and will accelerate the reaction.

The reaction will destroy the surface of the shell and cannot be reversed. However, changing the environmental and storage conditions can stop the reaction from occurring and prevent further loss.

The overall appearance on the surface of a shell may look very similar to mold. It is described as initially appearing as white, rough, chalky, or fuzzy in patches; perhaps with streaks or spots. These are easiest to see on dark and smooth shell surfaces. Though it may look mold-like, microscopic examination will show a structure that looks distinctly crystalline and mineral – not biological. A vinegary smell in the storage area is another clue. Acetic acid (formed when wood breaks down) is also the main component of vinegar and it’s smell indicates the presence of this vapor and the potential for Byne’s “disease.”

At the Alaska State Museum, we tried an experiment to force Byne’s Disease with little success. We gathered mussel, clam, and scallop shell from the beach, cleaned them, and exposed them to fresh oak sawdust. We tried this enclosed at room temperature, in a lab oven, and even added moisture to accelerate the reaction, but after 8 weeks we did not have drastic crystal formation.  This suggested to us that Byne’s disease formation may take a long period of poor storage. One shell, however, did grow a nice mold sample at high humidity!

3. REFERENCES

National Park Service. (2008) “Byne’s “Disease:” How To Recognize, Handle And Store Affected Shells and Related Collections.” Conserve O Gram. August 2008, Number 11/15.

Crista Pack’s notes: Conserve O Grams provide a great model for how to write a concise, informative article that is useful to conservators and non-conservators alike. Topics covered include history, causes, problematic materials, identification, cleaning, and prevention.  “Byne’s disease” can occur in any natural history specimen composed of, or including calcium carbonate. This includes …limestone-based rocks and fossils.” Includes a great Table listing damaging materials that have been used in museum. “Health and Safety Warning: Calcium acetate and calcium formate…are not the same as common table salt (sodium chloride). NEVER taste these salts, even though you may see this recommended in older literature.”  The salt crystals are water-soluble and may be removed with a brief soak or gentle brushing under running water.  Alcohol, boiling, freezing or microwaving, are NOT recommended.  If storage environment is not altered, the process will start again.

Tennent, Norman H. and Thomas Baird. (1985) “The Deterioration of Mollusca Collections: Identification of Shell Efflorescence.” Studies in Conservation Vol.  30 pp.73-85.

Crista Pack’s notes:  Begins by providing definitions for efflorescence, the methods that have been used to analyze them (XRD, IR, TGA and NMR spectroscopy), and provides the chemical formulas for different components.  The authors also discuss the cause of efflorescence formed on shell from exposure to acetic and formic acids (from wood cabinets). Gives a really good overview of methods used for analysis and descriptions for how the efflorescence forms on different types of shells (patterns, similarities between different shells, natural protective coatings that inhibit growth in some areas, etc.).  Provides some interesting discussion on how NaCl (salt) enhances growth – salt from ocean or salt from washing/boiling shells in salt water which was occasionally done. Page 76 contains excellent images of examples. There is a large section dedicated to the technical analysis studies and the data that was acquired from them. This was a little too in-depth for the scope of this project, but would be useful for anyone with access to this kind of analytical equipment and would like a comparison. The conservation section was short, but touches on the pros and cons of cleaning off efflorescence. More could have been said about the potential damage that could occur from removing efflorescence , as well as something – even just a short statement – about ethics of removing original material. Also gives a short statement about the need for safe materials to be used in the storage of artifacts and refers readers to Blackshaw and Daniel’s article “Selecting Safe Materials for use in the display and storage of antiquities.”  Another method for preservation given is coating the shell, however the article unfortunately fails to mention what shells can be coated with.

Wikipedia. “Byne’s disease.” Online: http://en.wikipedia.org/wiki/Byne’s_disease. Accessed June 29, 2011; last modified on 14 November 2010 at 03:52.

Crista Pack’s notes: While all Wikipedia articles have to be taken with a grain of salt, this one is particularly good in its depth of coverage on the topic and easy-to-understand explanation of the deterioration. It also contains a good list of references with links to pdf articles and a number of good images.

4. EXAMPLES IN ALASKA