Posts Tagged ‘insects’

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

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Under Construction, August 2011

1. BACKGROUND

The Alaska State Museum has many garments and artifacts made of textile from various periods and cultures over the past few centuries. The Tlingit of Southeast Alaska have woven with mountain goat wool and cedar bark for hundreds of years, if not longer. Some items from the Russian period survive.  Military uniforms, various kinds of outdoor gear, quilts, and dolls are common as well.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan textile or fiber artifacts is insect debris such as cocoons and frass.  Casemaking clothes moths and webbing clothes moths are the biggest threat. Mold and lint are two other common possibilities.

3. REFERENCES

4. EXAMPLES IN ALASKA

Conservators at the Alaska State Museum are regularly asked this question:

“What’s that white stuff?”

Disfiguring white stuff on artifacts and artworks can be the result of a wide range of causes. These are referred to by a variety of terms including: efflorescence, bloom, fatty bloom, spue, blushing, chalking, blanching, haze, dust, grime, salts, mold, transferred images, crizzling, sweating and patina. While these terms each refer to specific types of damages and disfigurements, they are often used interchangeably. This may be due to the similar appearance many of them have at first glance. White fuzzy material on an artifact is often assumed to be some type of mold. Sometimes this is the case, but a number of other things can have the same appearance. Staff at the Sheldon Jackson Museum were concerned that Tlingit hide armor was breaking out with mold. Small white fuzzy patches were disfiguring the surface, and the problem seemed to be getting worse. However, upon examination, the white substance was waxy and records indicated a leather dressing treatment was undertaken in the late 1960’s. At the time, leather dressings were a common part of museum practice and believed to benefit leather by aiding flexibility. Over time, the fats can alter and come out of the leather as a bloom or spue, disfiguring the surface. Leather dressings are no longer part of museum conservation practice.

A wooden dish in the Alaska State Museum collection has a fine sugary-looking white deposit inside. Examination and history of the dish reveal the crystals are related to the bowl’s history as a vessel for holding grease or oil. The presence of those crystals is part of the history of the artifact and tells a story.

GETTING STARTED

“What’s that white stuff” is a great question. Does it belong there? Is it hazardous to humans? Is it destroying the artifact? We suggest a systematic approach to the problem.

  1. Identify the material affected. What is your artifact made of? Our INDEX lists artifact materials vulnerable to “white stuff.”
  2. Examine the context and history of the artifact. What was it used for? How was it maintained? Was it dug out of the ground? Has the environment been stable? Has it been on exhibit? Also ask folks who have worked at your museum a long time. These clues may help narrow down possibilities. Write them down.
  3. Characterize the appearance of the white stuff. Is it powdery? Sticky? Flaky? Is it a haze or a crust? Does it appear in a pattern? Use our list of descriptive words below to help you. Write it down. Take a photo for the files.
  4. Consider the typical POSSIBILITIES. For each kind of material, there are certain kinds of white stuff that we have see more than others in Alaskan collections. We try to list these in the INDEX by material.
  5. Test the hypothesis. Make a guess at what you think it is, and if you can remove a little bit, test your theory.

HOW DO I DESCRIBE WHAT I SEE?

Here’s a list of vocabulary words that can help you characterize what you are looking at.  These words, plus a photo, can help others work on solving your mystery. Check GLOSSARY if needed.

airy

branched

chalky

cloudy

crumbly

crusty

crystalline

dotted

dry

fibrous

filmy

foamy

fuzzy

glossy

grainy

greasy

hard

hazy

matte

opaque

powdery

rough

spidery

spotty

sticky

soft

sugary

translucent

HOW CAN I ANALYZE MY WHITE STUFF?

EASY

  1. Magnifying glass and strong light. Look carefully at the surface and try to characterize the appearance. Is it an optical effect from delamination or abrasion? Or is it accumulated on the surface, indicating an accretion or efflorescence?
  2. Does it roll easily on a tipped surface, like tiny dry balls?  You may have insect frass.
  3. Look for patterns on the surface or an explanation for why the white stuff is in some areas and not others. Consider different materials, which side is “up” and if the pattern may be associated with something applied as a liquid.
  4. If you can sample it with a small pointy tool, note how difficult it is to remove. Powdery? Crumbly? Sticky? Smeary?  This is an important clue. Don’t remove it all during sampling, you may want to try again with another idea.
  5. If you have removed a bit of it, try rubbing some of it on a clean glass surface. Does it smear? Or does it stay crumbly/powdery? A smearing substance can indicate the presences of fats or waxes and may indicate the sample is some type of fatty bloom.
  6. Try adding a drop or two of water, enough to cover the sample. Does it dissolve? If so, it may be a water-soluble salt.
  7. With another sample, try adding a drop or two of mineral spirits.  Does it dissolve now?  Perhaps it is something waxy.
  8. If the sample melts with gentle heating, it may be a wax or bloom. Melting can be done over a hotplate, or even with a bit of foil over a candle.

TRICKY:

  1. If you have a binocular microscope, you can see more detail. For example, branching structures of mold may be visible. Crystals may be evident. Bug parts are more obvious under magnification.
  2. If you have a polarized light microscope, you can see even more detail and observe optical properties. Fruiting bodies confirming mold may be present.

HARD:

  1. Various kind of instrumental analysis may be available at larger museums or universities.  For example, an XRF can identify certain heavier elements that point to specific possibilities like metal corrosion, pesticides etc.
  2. If you are equipped to use acids safely, add a couple of drops of HCl. If your sample bubbles vigorously, it may be a carbonate. Maritime accretions and insoluble archaeological salts often bubble with this test.
  3. While some resources may suggest tasting the salt to confirm that is what it is…this is not a good idea and tasting should never be done to identify an unknown substance. The salts forms in Byne’s disease, for example, are not components of common table salt (sodium chloride) and should not be consumed.
  4. Spot testing can help characterize “white stuff” but you must be equipped with a chemistry lab and familiar with laboratory techniques to perform many of these tests. The main museum reference for these tests is:

Odegaard, Nancy, Scott Carroll, and Werner S. Zimmt. (2005) Material Characeterization Tests for Objects of Art and Archaeology.  Second Edition. Archetype Publications Limited. London.