Posts Tagged ‘crystals’

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

Under Construction, August 2011

1. BACKGROUND

Alaska Native and non-Native cultures have made extensive use of mammal fur for all manner of clothing, gear, and artwork. And one can hardly enter a museum, airport, or mall anywhere in Alaska without encountering stuffed mounts of iconic Alaskan animals. The website for the Alaska Fur ID Project includes information about the mammals most often used on artifacts in Alaskan collections.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan taxidermy is arsenic.  Arsenic is one of the more common pesticides found as residue on many types of objects. According to the National Park Service, arsenic compounds were frequently applied during the 18th – 20th centuries in the form of soap mixtures and sprays to preserve biological specimens and ethnographic objects (Conserve O Gram 2/3 2000,1). To identify arsenic, the National Park Service recommends to

“Look for powdery or crystalline deposits at the base of feathers and hairs, around eyes, in or at the base of ears, around mouth or bill, along ventral incision, at base of tail, and on foot pads. On ethnographic objects, inspect crevices and seams where arsenic may have collected. Even if deposits are not evident, all natural history specimens collected and prepared before the 1980s should be tested for the presence of arsenic.” (Conserve O Gram 2/3 2000, 2)

On fur, the most common white materials are associated with insects. Frass, webbing, cocoons, bug parts, shed larval skins and the like are often found in association with hair loss and even holes chewed through the hide. Occasionally there will be small widely spaced hard blobs adhered to the shaft of the hair down toward the skin, and I have been led to believe that those accretions are more likely from bugs that were bothering the furry creature while it was alive.  You may also see adhesives associated with tear repair from the skin side, such as BEVA 371 film and Reemay (a spun bonded synthetic fabric that is thin and web-like).

3. REFERENCES

_____(2010) “Appendix: Common Museum Pesticides” Pesticide Mitigation in Museum Collections: Science in Conservation: Proceedings from the MCI Workshop Series Smithsonian Contributions to Museum Conservation. Smithsonian Institution Scholarly Press Editor: Charola, A. Elena;Koestoer, Robert J. pp. 71-72

National Park Service’s Conserve O Gram on arsenic: http://www.cr.nps.gov/museum/publications/conserveogram/02-03.pdf

4. EXAMPLES IN ALASKA

Under Construction, August 2011

1. BACKGROUND

A huge range of wooden artifacts are found in Alaskan collections. These range from waterlogged archaeological remains, to traditional Native feast dishes and tools, to picture frames, furniture and fine carvings.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan wooden artifacts are fatty bloom, dust, mold, paint spatters, polyethylene glycol treatment, insect debris (such as frass) and pesticides.

Bloom

When seeing fuzzy white growth on an object, people’s initial assumption is often that it is a mold or mildew. But this is not always the case. Blooms can sometimes have a feathery or matted fibrous look similar to mold, but microscopic examination and solubility tests can confirm the presence (or absence) of bloom. White bloom resulting from fats, oils and waxes in wooden materials may be referred to in literature as ‘fatty bloom,’ ‘fat bloom,’ or ‘fatty spew (or spue). These terms all refer to the formation of crystals on the surface that form from fats or oils either applied to the surface or left as residues from use.

Bloom on wooden artifacts is caused by the application of fats and oils to the surface or from residues left behind from use. There are a number of hypotheses regarding the exact mechanism of the formation of these blooms. Some attribute it to free fatty acids that separate out and crystallize on the surface.(Ordonez and Twilley 1998, 3-4). Analysis by Scott R. Williams (1988, 65-84) found bloom on objects to be primarily composed of a variety of fatty acids including palmitic, stearic, myristic and dicarboxylic acids (such as azelaic). These were present individually or occasionally as mixtures; however palmitic and stearic were the most commonly found (Williams 1988, 68-69). In general, however, it is believed that temperature and humidity levels play important factors in the migration and crystallization process.

Bloom can have a variety of appearances depending on the storage conditions, fats present in or on the object, and the type of material the bloom is forming on. It can appear powdery, granular, or branch-like. This makes it easily confused with other types of white stuff that can be found on objects. Throughout our survey, the most common type of bloom found on wood artifacts had a very crystalline, almost sugary appearance to it. In some cases it had been partially rubbed off the surface. A wide variety of wooden trays, bowls, dippers, ladles and spoons traditionally made by Alaska Native cultures were used in connection with animal oils such as seal oil or eulachon oil. These dishes often, but not always, have a darkened surface from the oil as well.

An important note is that fat bloom is often primarily found on areas of an object exposed to air. For example, on a leather-bound book the spine of the book (if it faces outward) may have the heaviest bloom. In some instances, it has been found that items closer to an air conditioning vent had a higher occurrence of bloom (Gottlieb 1982, 37) indicating that air circulation, temperature, and humidity play an important role.

Mold

Mold is typically described as having a fuzzy, velvety, or sometimes slimy appearance. When viewed under a microscope, the vegetative part of mold (known as mycelium http://en.wikipedia.org/wiki/Mycelium) can be seen as thin, thread-like branching hyphae and is very distinctive from the crystalline structure of salts.  Mold growth generally begins to occur on organic materials when the environment is at 70% relative humidity or higher. The Canadian Conservation Institute (CCI) gives the following useful chart for mold growth on their “10 Agents of Deterioration” website http://www.cci-icc.gc.ca/crc/articles/mcpm/chap10-eng.aspx:

Pesticide Residue

Up until the late 20th century, the application of toxic pesticides to organic materials in museum collections was a widespread and accepted practice. Compounds made of arsenic or mercury were sometimes sprayed or dusted onto artifacts to prevent pest damage. DDT was also common as were moth balls comprised of dichlorobenzene or naphthalene. The carcinogenic and hazardous nature of these chemicals is now known and they are no longer used. However, the residues of past applications remain and they can sometimes show up as white residues that may be confused with other salt formations. On wood, pesticide residues may appear as a whitish, spotty haze over the surface of the object. When handling objects made of organic materials such as skin, it is always better to err on the side of caution and protect yourself from possible exposure to toxic chemicals. Wear protective gloves and a lab coat or apron. You may wish to wear a dust mask to prevent breathing in toxic dust.

Pests/Frass

Frass is the excrement passed by insects. It can be fine and powdery to grainy and pellet shaped in appearance. Frass often takes on the color of whatever substance has been eaten. In the case of light colored woods, if the frass is seen against a dark background, it can appear very light in color and might almost seem white or off-white. Yellow or beige may be more typical.  One type of wood boring beetle is the Anobiid, also known as a powderpost beetle. These insects can be found tunneling their way through wood objects and leave behind frass that looks like tiny, lemon-shaped pellets. They are light tan in color, but may look whitish against a dark background. These insects were responsible for an extensive infestation of the Sheldon Jackson Museum collection many decades ago. More information on the Anobiids can be found on the museumpests.net website: http://www.museumpests.net/pdfholder/34image.pdf

3. REFERENCES

Mold hyphae, image by Bob Blaylock

Erickson, Harvey. (1977) Preservation of Wood Artifacts. Seattle, WA: University of Washington College of Forest Resources, October 1977.

Crista Pack’s notes: A very dated publication that reflects the acceptance and use of pesticides such as arsenate and boric acid compounds and DDT. Useful for its historical context to understand what may have been applied (and how) to wooden artifacts at that time. Erickson also discusses some different types of species (and their frass) that had been identified as potentially damaging to wood collections.  The possible discoloration and efflorescence that may develop from application of the various pesticides is discussed; although the latter is not seen as a particular problem, but rather something that can simply “be largely removed by brushing and moist cloths.”

Geier, Katharina (2006) “A Technical Study of Arctic Pigments and Paint on Two 19th Century Yup’ik Masks.”  Journal of the American Institute for Conservation. Vol 45 No 1 Spring 2006.  Pp. 17-30

Ellen Carrlee’s notes: White pigments used on masks were identified as a mixture of clays, micas, and associated minerals, consistent with reportings in the ethnographic literature.

Ordonez, Eugenia and John Twilley, John.  (1998) “Clarifying the Haze: Efflorescence on Works of Art” WAAC Newsletter 20 (1) 1998 pp 12-17.

Pearlstein, Ellen. “Fatty Bloom on Wood Sculpture from Mali.” Studies in Conservation 31 (1986) 83-91.

Crista Pack’s notes: describes the blooms found on African wooden objects. Results show that the bloom was the result of ethnographic application of oils. Examination techniques used include melting point, solubility behavior and infrared spectroscopy. States that sampling technique involved removing surface material with a fresh scalpel blade into a well slide.  Provides a really good description of the bloom mechanism and polymorphism. Within conclusion, notes that “The surest way to eliminate the bloom entirely would be to remove all of the material causing it, which is neither simple on a porous wood sculpture, nor necessarily desirable if the material is a fat of ethnographic origin.” Also notes that the application of conservation waxes can interfere with identification and cause confusion because their chemical composition can be similar to fats. Gives really great technical data on the results of the fats analyzed, but these appear to be mainly of African origin. Oils in Alaskan wooden dishes are often of marine origin, including fish and marine mammals.

Williams, R. Scott. (1989) “Blooms, Blushes, Transferred Images and Mouldy Surfaces: What Are These Distracting Accretions on Art Works?”  In Proceedings of the 14th Annual IIC-CG Conference 1988.  Edited by Johanna G. Wellheiser. Ottawa. Pp. 65-84

4. EXAMPLES IN ALASKA