Posts Tagged ‘spew’

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

Under Construction August 2011

1. BACKGROUND

Stone artifacts are most commonly seen in Alaskan collections as tools, projectile points, oil lamps, fishing gear, and argillite carvings.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan stone artifacts is salts from burial or contact with seawater, fatty materials from contact with oils, or adhesive residues from old repairs or attempts to stick down an artifact during exhibition. Stone oil lamps were common in Alaska and oil from marine mammals was typically the fuel.  This may result in fatty bloom from those oils.  Many of these lamps also come from an archaeological context, or even beach context, suggesting possible salt efflorescence.

3. REFERENCES

Pearson, C. (1987) “Deterioration of Ceramic, Glass and Stone” Conservation of Marine Archaeological Objects.  Butterworths.  London.

4. EXAMPLES IN ALASKA

Under Construction, August 2011

1. BACKGROUND

Leather refers to the skins of animals that have been tanned or semi-tanned for use. There are many types of leather tanning (http://en.wikipedia.org/wiki/Leather#Forms_of_leather) which give skins different looks and feels. Since leather is an organic material, it is susceptible to many different forms of deterioration. Some can cause white stuff to appear on the surface, which may be difficult to distinguish from one another.

In Alaskan collections, there are various kinds of tanned and untanned skins and hides. Tlingit armor, fishing nets, gutskin parkas, babiche snowshoe lashings (made from moose or caribou rawhide), boots, tool lashings, model and full-sized kayaks, drums, and military gear are among the most common leather items.

2. POSSIBLE CAUSES

Fatty Bloom

The most common white stuff we have seen on Alaskan leather items is white bloom resulting from fats, oils and waxes and may be referred to in the literature as ‘fatty bloom,’ ‘fat bloom,’ or ‘fatty spue (or spew)’. These terms all refer to the migration of fats/oils through the leather material that crystallize on the surface in the presence of air. 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.

Bloom can be considered as being Primary or Secondary.   Primary bloom results from fats used during the tanning process and can be considered as an inherent vice of the material. Manufacturing flaws contribute to Primary bloom and can cause mineral salts to exude or fat bloom to develop through insufficient degreasing methods during production. Secondary bloom is caused by the application of fats and oils to the surface of the leather. At one time, it was believed that applying leather dressing or other kinds of soaps and oils to a leather surface would extend the life of a leather object. Now it is known that this is not the case and often the application of such substances can do quite a bit of damage

There are a number of hypotheses regarding the exact mechanism of the formation of these blooms. Some attribute it to free fatty acids migrating through the leather (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).

Others have cited lactic acid, produced from the presence of potassium lactate in leather dressings, as the principle component of white efflorescence on leather (Gottlieb 1982, 39). In general, however, it is believed that temperature and humidity levels play important factors in the migration and crystallization of whatever is moving through and out of the leather.

Bloom can look powdery or gummy in appearance. Powdery bloom can be caused by either the natural fat of the hide or fatty materials applied to the leather. A number of variables are implicated in the formation of powdery bloom. These include: temperature, humidity, acidity of the leather, or materials used during the tanning process. Sticky or gummy bloom is believed to be caused by oils that are highly oxidizable, such as fish oils. If these kinds of oils were used during processing (and incompletely removed) or applied later, then they may cause sticky white bloom. High temperatures and humid environments, as well as exposure to air and light can accelerate these formations.

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.

Salt Effluorescence

Salt efflorescence is less common as a culprit on leather objects, but can occasionally be found on leather as inorganic salt spues. Leather items that have been worn (or in contact with perspiration in any way) may develop salt efflorescence as the salts migrate through the leather and crystallize on the surface.

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:

Corrosion

Metal items in contact with leather can react with the fats and oils, creating organo-metallic corrosion products. Quite frequently, the metal in question is a copper-alloy and therefore the corrosion products building up will be a bright green instead of white.

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. 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.

Use-Related White Stuff

Previous treatment of the artifact during use could be a cause of white accumulation on a leather surface. It is important to determine who performed the treatment and when, especially if an object is being considered for cleaning. If the treatment was done by the person who created the item – and it was part of the object’s use history, then it will likely be inappropriate to remove it. The loss of information involved in removing material will have to weighed against any benefit for cleaning an object. An example of an original treatment would the application of clay, flour, baking soda, or other similar substance by Native American groups to brighten and whiten a darkened or stained hide.

Catalog number II-A-77 is a Siberian Yupik pipe and tobacco bag in the Alaska State Museum collection. Tobacco and snuff production sometimes includes the addition of alkaline salts such as potash (often potassium carbonate). Could this be the white material we see on the leather bag? The pipe bowls, mouthpieces and decorative elements of the pipe are usually made from lead, which forms a white corrosion product. Museum leather care protocols decades ago called for applications of fats and oils to help leather remain supple. Proper identification of this white material would help us know if we ought to remove it or not.

3. REFERENCES

Mold hyphae, image by Bob Blaylock

Fogle, Sonja. “Neat’s-Foot Oil in Commercial Products.” Leather Conservation News. Vol. 2, No 1, Fall 1985.

Crista Pack’s notes: Article provides overview and definitions for classes of neat’s foot-oil. More information can be found in his article “The Saddle Soap Myth,” which was reviewed in Leather Conservation News, No. 3.

Gottlieb, Jean S. (1982) “A Note on Identifying Bloom on Leather Bindings.” Journal of the American Institute for Conservation, Vol. 22, No. 1 (Autumn, 1982), pp. 37-40. Stable URL: http://www.jstor.org/stable/3179717. Accessed: 27/06/2011.

Crista Pack’s notes:  This article discusses the finding of white bloom on a number of pre-1850 leather bound books. The author notes “a greater incidence in the general vicinity of one or two of the air conditioning ducts. “ Also that, “Sheepskin bindings and other older porous leathers showed the heaviest concentration of what appeared to be crystals, mostly on volumes that had been treated with potassium lactate and neatsfoot oil/lanolin within the past twenty-five years.” And “The surfaces exposed to the air (such as backbones) were those most densely coated with the bloom.” (p37)

The authors developed two hypotheses: “1) salts of lactic acid are always present in tanned leather, and may precipitate either in response to atmospheric changes, or from other causes; 2) the lactates identified in these samples appear to be residues of some substance introduced into or onto the leather (e.g., potassium lactate). “

Variations of tanning procedures and types of skin have to be considered with Hypothesis 1. For Hypothesis 2 “we must allow for variations in leather composition and condition, as well as the amount of substance applied, and stability of atmospheric conditions in which the books are kept.” (38)

Based on the NMR spectra obtained on samples analyzed, the author “identified a principal component of the efflorescence on the books as lactic acid, and have also pinpointed the source of this lactic acid as potassium lactate.” (39) And “the potassium lactate-neatsfoot oil/lanolin treatment was begun at the University of Chicago in the late 1950’s.” (39)

 “There appears to be a correlation between the amount of efflorescence on leather volumes and their proximity to circulating air from ducts or vents. Since potassium lactate is deliquescent, air passing over surfaces holding a solution of potassium lactate and water would, by carrying the water off as vapor, cause the potassium lactate salts to be drawn to the surface: (KL · H₂O)hq à(air)à KLS + H2O (circulating air)” (40)

Doesn’t really clarify if any of the finding support Hypothesis 1, but seems to imply that Hypothesis 2 definitely has something to do with the production of bloom and, specifically, the presence of potassium lactate to create lactic acid is an important factor.

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

Plenderleith, H.J. (1956) The Conservation of Antiquities and Works of Art.  Oxford university Press London.

Ellen Carrlee’s notes: Mentions the museum use of potassium lactate solution for protection of vegetable tanned leather and British Museum Leather Dressing for enhancing flexibility of leather.  Recipe for BM leather dressing includes lanolin, cedarwood oil, beeswax and hexane.  Described as a yellow cream when applied.

Stambolov, T.(1969) “Manufacture, Deterioration and Preservation of Leather: A Literature Survey of Theoretical Aspects and Ancient Techniques.” ICOM, The International Council of Museums Committee for Conservation. Plenary Meeting. Amsterdam: Central Research Laboratory for Objects of Art and Science, September 15-19, 1969.

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