Posts Tagged ‘salt’

Under Construction August 2011

1. BACKGROUND

Most ceramics we see in Alaska have a porous structure that can allow water soluble salts from the ground or from seawater to penetrate. When the water dries, these salts can crystallize on the surface. If the item is glazed, the salts can cause the glaze to pop off the surface in small spalls because the glaze is made of glass and is not porous. Alaska Native cultures have few traditional ceramic technologies, with the major exception of a coarse, heavily tempered ceramic. Historical ceramics from the Russian period, through the gold rush and homesteading periods up to modern times are seen in Alaskan collections.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan ceramics tends to be salts from burial or contact with seawater. Adhesive residues are also common and are usually associated with the break edges. Adhesive residues from labels have also been seen. At the Alaska State Museum, we attempted to force salt crystal growth on ceramics. We gathered high-fired ceramic china from the beach site of the old Treadwell Mine dining hall on Douglas Island, but could not get any crystals to appear on that ceramic. At the same site, which is subjected to tidal action, we also buried a smashed contemporary terra cotta flowerpot for several days.  That pottery readily yielded nice crystal salt growth after only a short time in the lab oven. 

3. REFERENCES

Harry, K.G. and L. Frink. (2009) “The Arctic Cooking Pot: Why Was it Adopted?” American Anthropologist 111(3):330-343.

Harry, K.G., L. Frink, B. O’Toole, and A. Charest. (2009) “How to Make an Unfired Clay Cooking Pot: Understanding the Technological Choices Made by Arctic Potters. Journal of Archaeological Method and Theory 16 pp.33-50.

Frink, L. and K. Harry. (2008) “The Beauty of “Ugly” Eskimo Cook Pots.” American Antiquity 73(1):103-120.

Paterakis, A.B. (1987) “The Deterioration of Ceramics by Soluble Salts and Methods for Monitoring their Removal.” In Recent Advances in the Conservation and Analysis of Artifacts.  Institute of Archaeology, Jubilee Conservation conference pp67-72.

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

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

Under Construction August 2011

1. BACKGROUND

Glass structure is composed primarily of silicates and can remain stable and relatively unchanged for hundreds, if not thousands, of years if cared for properly.  Unfortunately, even with the proper care, this is not always the case as some glass is known to deteriorate rapidly over time.

 On a chemical level, most glass is stable.  However, some glass artifacts are known to undergo a complex disintegration.  This chemical breakdown of glass is commonly known as glass disease.  When discussed in reference to the most ubiquitous of archaeological and ethnographic artifacts, the glass bead, it is often termed ‘bead disease’.

The main component in glass is silicon dioxide, also known as silica.  Silica occurs naturally in three forms.  Its solid form is known as quartz, its amorphous or non-crystalline form is known as opal, and it is commonly found in its impure form as sand.  Glass can be made from pure silica, but it has a very high melting point of 4,172 ° F – which makes it rather difficult to work with directly.  For this reason, most glass mixtures have traditionally contained 70-74% silica and 16-22% of an alkali material, which serves to lower the glass melting point. Quite often, the alkali material used was either soda ash, a sodium carbonate which is obtained from burnt plant material, or potash, a potassium carbonate usually derived from wood ash. 

The sodium carbonate in soda ash produces a clearer glass than potash, so it was – and still is – more commonly used in glass manufacture.  However, when sodium carbonate is added to silica, the resulting glass is water soluble – meaning it will dissolve in water.  This is generally an undesirable characteristic for glass.  For that reason, lime (calcium oxide) is often added along with other minerals for better durability.  The addition of lime also helps the different components to mix together more easily.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan glass artifacts is glass disease (crizzling, weeping) on beads. Abrasion, ghosting, mold, and previous treatments have also been seen on glass.

Glass Disease

While glass disease is seen on various kinds of glass objects, the most common Alaskan artifacts we have seen it on are glass beads. This damage might be historically interesting, as it might suggest a very old bead.

By the 16th century in western Europe, the production of glass (and beads in particular) became central to the economic and political endeavors of the time.  According to Lois Sherr Dubin, (2009, 29) “For Europeans, whose aim was to maintain maximum profits with a minimum commitment of manpower and resources, glass beads, exchanged for American furs or African ivory, gold, and slaves, yielded enormous margins – 1,000 percent was the return on investment, according to a report in 1632 – and thus became a central part of international trade patterns.”  

For a long time Venice was the center of glass bead production in Europe.  In 1292 A.D., glass production was moved from Venice to the nearby island of Murano in an effort to keep their production methods completely secret as well as to protect Venice from the risk of fires from the now constantly burning glass furnaces.  Production continued to increase throughout the centuries and bead making techniques were adjusted to meet the increasing demand and to decrease production costs as much as possible.  Chemical compounds that were added to glass mixtures to lower the glass melting point began to be added in even larger amounts.   This reduced the amount of fuel needed to run the furnaces and sped up the process overall.

As mentioned above, most glass consists of approximately three-quarters silica with sodium carbonate added to lower the melting point and calcium oxide to stabilize the mixture. If this combination is kept in balance, the glass is likely to remain stable. However, when there is an imbalance in the proportion of these components, problems can arise.  If there is an excess of alkali and too little lime (as was happening in Murano), the surface of the glass may begin to react with moisture in the air and start to break down.  This is the major cause of glass disease.

Glass disease is therefore inherent in the chemical makeup of certain glasses.  This is both good and bad news.  The good news is that it can’t spread to other glass in your collection– it’s not contagious. The bad news is that if the chemical composition of the bead lends itself to glass disease, there is nothing that can be done to stop it from breaking down.  The corrosive nature of glass disease causes a snowball effect of sorts on objects that succumb to it.  Once the process begins, there is no known treatment that can reverse the effects or stop it from proceeding.  The degradation can be slowed down considerably with cleaning and careful monitoring of the storage environment, but nothing will “cure” it, so to speak.

At the present time, it is not fully understood how this decomposition of glass proceeds on a molecular level.  However, we do know that in all glass the sodium and potassium carbonates are hygroscopic.  This means that they readily take up and retain moisture from the air.  Once these salts become hydrated, they can leach out of the glass and form crusty deposits on the surface.

As the sodium and potassium ions are removed from the chemical structure they are replaced by hydrogen ions, which diffuse throughout the glass.  This creates a hydrated silica network which is inherently weaker.  As the deterioration of the glass progresses, the surface of the glass becomes increasingly alkaline.  An alkaline substance is one the measures above 7 on the pH scale.

A bead with glass disease will show many symptoms, some of which can be seen easily and others that may require the use of a magnifying lens or microscope.  There are five signs of glass disease which are commonly cited by conservators.  These are: broken beads, sweating or weeping beads, white crusty deposits, crizzling, and damage to the backing material.  Additionally, as glass begins to deteriorate, it will quite often have a dull, foggy appearance.  This results from deposits left on the surface of the glass, as well as crizzling altering the reflectivity of the glass.

In certain environments, droplets of moisture may appear on the surface of a glass bead.  This is known as sweating or weeping.  This occurs when atmospheric moisture combines with the alkali material used in the manufacture of the glass and causes the hygroscopic alkali salts leech out.  These salts migrate to the surface forming a soapy, sticky alkaline solution.  This soapy residue forms abrasive and caustic by-products, which draws dust and dirt to the surface.  This in turn attracts more moisture to the glass and facilitates the progression of the glass bead deterioration.  Glass beads may have a white, fuzzy look to them as salts from these residues crystallize, as well as from the dust and dirt attracted to the soapy alkaline residue. 

Unstable glass and high humidity can also result in the formation of crusty deposits on the surface of beads.  As discussed earlier, alkaline products that migrate out of the beads turn into alkaline salts, which are left on the surface of the bead or adjacent material.  This produces a hard alkaline coating which can give glass a white, dusty appearance.

As the deterioration of unstable glass progress, small fissures in the surface of the glass start to become visible.  This is known as crizzling and it is characterized by a fine all-over cracking or fracturing of glass.  This step in the degradation of the glass can also lead to flaking and pitting on the surface of the bead.  Crizzling of the glass surface can cause transparent beads to look opaque and also contributes to the appearance of a whitish haze.

It is not known for sure whether or not glass disease occurs in some colors and/or sizes of beads more than others, but our experience through this survey of Alaskan beads is that it might.

Abrasion/scratches

The most common problem associated with caring for historic glass, including glass beads, is their fragility.  Like all glass objects, glass beads can crack, break, or become easily scratched if they, or the objects to which they are attached, are not carefully handled. Abrasion and scratches interfere with the way light passes through the glass and can cause a whitish, opaque haze. Think of glass fishing floats, for example, which can appear hazy if they have been abraded by sand.

Ghosting or transferred images

The reason that transferred images are sometimes referred to as “ghosting” is because a replica of the image can usually be seen in the glass. These images and other blooms on paintings are sometimes attributed to mold due to the microenvironment that exists between a painting and it’s glazing (Williams 1988, 66). It seems rather unlikely, however, to have a mold that grew in such a specific pattern as to duplicate an image. When the white accretions making up transferred images were analyzed in the 1980s, they were discovered to be made primarily from ketones and sodium soaps (Williams 1988, 69). The overall hypothesis for this is that ketones volatilize from the paint, condense on the glass and then oxidize into carboxylic acids. These acids then react with sodium in the glass to form the sodium soaps that make up the images (Williams 1988, 70). This is a similar reaction to that found happening in glass beads – particularly those in contact with lipid-containing ethnographic materials. It’s worth noting that in many cases where an artwork came into contact with glass, no transfer image was formed. Rather, a halo of clear glass remained around the point of contact with the transfer image forming again beyond this halo (Williams 1988, 68).  Williams describes the primary melting point of the transfer image material analyzed as being consistently at 69°-70° C (1988, 67). Since the transfer images are composed of organic compounds, they have poor solubility in water. To test this, take a small sample of the white stuff and place it on a glass slide or similar. Add a couple drops of water. If the compound does not appear to dissolve, this would rule out a soluble salt and may indicate the presence of insoluble organic compound.

mold

Mold is typically described as having a fuzzy, velvety, or sometimes slimy appearance. Mold needs organic material to feed on, so glass doesn’t commonly provide the necessary ingredients. Glass used to frame a photo at the Alaska State Museum once had branch-like mold on the inside of the glass, suggesting the gelatin of the photo might have provided enough nutrients for mold. Glass beads strung on sinew or cotton thread might also provide adequate nutrition and you might see mold growing out of and around the beads – especially if the threads/sinew have absorbed moisture and created high RH microenvironments inside of the beads. Additionally, dust and grime that accumulate on glass can provide the necessary materials to allow for mold growth. Mold was once seen on the glass touching the surface of a framed photograph at the Alaska State Museum. 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:

Previous treatment

Different types of treatments may have been used in the past on glass beaded objects that could cause a white or hazy appearance. Adhesives may have been used to reattach beads, and these often can look cloudy and opaque as they age. Pesticide residues can create a whitish haze over the surface of materials, including beads. Pesticides were commonly applied during the early 20th century to collections containing natural history specimens and ethnographic artifacts made of organic materials such as leather, fur, and feathers.

3. REFERENCES

Mold hyphae, image by Bob Blaylock

http://en.wikipedia.org/wiki/File:20100815_1818_Mold.jpg

Carroll, Scott and Kelly McHugh.  (1999) “Material Characterization of Glass Disease on Beaded Ethnographic Artifacts from the Collection of the National Museum of the American Indian.”  Ethnographic beadwork: Aspects of Manufacture, Use and Conservation. Edited by Margot M. Wright. Conservation Centre, National Museums and Galleries on Merseyside on 22 July 1999

Ellen Carrlee’s notes: Most impacted beads fell into one of two categories: waxy/crusty beads that tested positive for triglyceride oils and powdery/crystalline beads that did not.  Sometimes kaolin clays used to whiten leather show up as white powder on beads but are not harmful.  Spot testing was also able to ID chlorides on beads throught to have contact with salt water.

Dubin, Lois Sherr (2009) The History of Beads from 100,000 to the Present.  Harry N Abrams, Inc.  New York.

Fenn, Julia.  (1987) “Deterioration of Glass Trade Beads in Contact with Skin and Leather or Glass Beads in Soapy Bubble.”  ICOM Committee for Conservation 8th Triennial Meeting, Working Group 3 Ethnographic Materials. Sydney Australia. Pp 195-197.

Jenkins, Michael R. “Glass Trade Beads in Alaska.” Alaska Journal  2.3 (1972), 31-119.

Crista Pack’s notes: Date for beads entering Alaska is unknown; however trade may have brought them into the region long before the first contact with non-indigenous explorers. Gives an insightful and thorough history of bead trading and the value of beads along the NW coast. Provides many images of different types of bead and objects beads were used in the manufacture of.

Lougheed, S. (1988) “Deteriorating Glass Beads on Ethnographic Objects: Symptoms and Conservation.”  Symposium 86: The Care and Preservation of Ethnographic Materials Editors R. Barclay et al Ottawa, Canadian Conservation Institute. Pp. 109-113.

Ellen Carrlee’s notes:  Controlling RH is the best solution for beads that exhibit early symptoms of glass dieases such as broken beads, sweating beads, crusts on bead or thread, crizzling, bleached spot below the bead on a textile, darkening of leather in contact with the bead. RH should be between 35% and 42% ought to control it.  Below 30% crizzling may occur, and above 42% alkaline carbonates that leach to the surface become hygroscopic and accelerate the process.

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

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

Sirois, P. Jane. (1999).  “The Deterioration of Glass Trade Beads from Canadian Ethnographic and Textile Collections.”  The Conservation of Glass and Ceramics: Research, Practice and Training.  Norman H. Tennant editor.  James & James.  London. Pp. 84-95

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

Under Construction August 2011

1. BACKGROUND

There is a wide variety of metal artifacts in Alaskan museum collections.  Tlingit copper daggers and carved silver jewelry, Siberian Yupik lead pipe bowls, Russian axe heads, aircraft engines and maritime artifacts are but a few examples.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan metal artifacts is corrosion. The most common white corrosion products are found on zinc (so-called white rust), lead, pewter, tin, and aluminum. Also seen on metals are polishing residues, which can cause corrosion stress cracking in brass if those polishing compounds contain ammonia. Those polishing residues often have a greenish white look and are in the crevices or carving details of the metal. Metals in association with leather sometimes corrode due to the oils present in the leather. Lead corrodes easily in the presence of certain pollutants, particularly volatile organic acids that may come from other collections artifacts or poor collections storage materials. In fact, a fresh lead coupon in a jar with suspected off-gassing materials is part of the so-called “Oddy Test” for poor storage materials. If white stuff appears on the lead, the material in question may be releasing pollutants. Siberian Yupik pipes are typically made with lead and many in the Alaska State Museum collection are corroding. The often have small leather or cloth pouches attached, and those sometimes have white crystalline formations on the outside.  We have tested one for lead, and come up negative.  However, the tobacco mixture sometimes contained birch tree fungus ash, assort of a potash.  Potash is chemically rich in potassium, and we did get a nice peak for potassium on our XRF analysis so possibly those white crystals on the pouch are related to the tobacco that was kept inside.  Some Tlingit rattles have been found to be filled with small pellets of lead shot to make the rattling sound. Aleut kayak models in our collection have kayaker hands made of lead, and those have corroded aggressively, including after treatment with a corrosion inhibitor called Incralac and coating with Acryloid B-72.  Remember that lead corrosion is poisonous, so wear gloves when handling.  We have also seen the drawer runners on some of our collections cabinets corroding, but have had trouble determining what the white corrosion product is and why those drawer runners are corroding.  We don’t want that white powder getting on our artifacts.  Similar white powder has been seen on aircraft engine parts in the collection, but those parts are likely made of aluminum. An interesting white metal issue we have not observed but may be possible in some collections is tin pest.  Tin usually appears as its stable beta form allotrope, but at low temperature pure tin can transform into another less stable form and become white and crumbly.  Tin must be fairly pure in order for this to happen, however, so it is rare. According to information added to Wikipedia in the past several years, the temperature needed is usually below 56F and may need to be sustained for over a year. Tin solder on cans, uniform buttons, and medieval organ pipes are cited as examples.  Different metals in contact with each other may experience galvanic corrosion.  In this case, one metal acts as an anode and the other as a cathode in the presence of an electrolyte. Zinc and aluminum for example, are often used intentionally as a sacrificial anode to corrode preferentially to more noble metals they are protecting. This situation can happen accidentally as well. 

3. REFERENCES

Selwyn, Lyndsie. (2004) Metals and Corrosion: A Handbook for the Conservation Professional.  Canadian Conservation Institute.  Ottawa.

Tennant, Norman H, Brian G. Cooksey, David Littlejohn, Barbara J. Ottaway, Steven E. Tarling, and Martin Vickers.  (1993) “Unusual Corrosion and Efflorescence Products on Bronze and Iron Antiquities Stored in Wooden Cabinets.” In, Conservation Science in the UK: Preprints of the Meeting held in Glasgow, May 1993.  Editor: Norman H. Tennant.  James & James Science.  London. Pp. 60-66.

Ellen Carrlee’s notes: there are many conservation articles on obscure and strange corrosion products on metals.  The small amount of sample usually available and the range of possible corrosion products makes identification of the corrosion product challenging and pinpointing the cause even more difficult.

4. EXAMPLES IN ALASKA

Under Construction, August 2011

1. BACKGROUND

Baskets are very common in Alaska, and are often used where ceramics might have been common in other cultures. Typically, baskets are made of plant materials such as spruce root, cedar bark, birch bark, or grasses. Archaeological basketry over 5,000 years old has also been found in waterlogged sites in Southeast Alaska, and several hundred years old on Kodiak Island.

2. POSSIBLE CAUSES

The most common white stuff we have seen on Alaskan baskets are dust, mold, adhesives, paint spatters, insect debris (such as cocoons) and PEG (polyethylene glycol.) Look with a magnifying glass to see how the white stuff is deposited. Powdery-looking spotty deposits may be mold. Dust would likely settle on certain areas that are horizontal, such as the lid if it has one or inside the base. The underside of the base may have accretions from adhesives, labels, or unclean shelves. Baskets were sometimes adhered onto an exhibit shelf in the old days to prevent them from moving with vibration of footsteps. Adhesives and repairs of various kinds have been used on baskets, so white stuff in association with a tear or loss is likely an adhesive. Waterlogged archaeological basketry was most commonly treated with a white glue in the 1960’s and 70’s, but since then polyethylene glycol treatments have been more typical.  Too much high molecular weight PEG (PEG 3350 or PEG 4000 for example) will result in white deposits on the surface.  These are soluble in warm water, and you can test this with a barely-damp cotton swab on the surface.  There was a period of time when “feeding” baskets with oil was a popular maintenance technique. This sometimes appears as white haze on baskets, and may also make them brittle. Haze could also be a pesticide residue. Always be careful to wear gloves…not only are you protecting the baskets from substances on your hands, you are protecting yourself from whatever may be on the basket.

3. REFERENCES

Hartley, Emily. (1978) The Care and Feeding of Baskets. Self-published.

Ellen Carrlee’s notes: Coating mentioned is paraffin oil in mineral spirits, 16% solution, p 29.  The author mentions that the techniques are derived from procedures developed by Bethune Gibson and Carolyn Rose of the Anthropology Conservation Lab of the Smithsonian’s Natural History Museum, and used there around 1974-75.

4. EXAMPLES IN ALASKA (click to enlarge images and see more info)