When the Dust Settles: Standardized soil mixtures and test dust products used in our cleaning study

Desiree Dolron. 2016. I will show you fear in a handful of dust II. Copyright Desiree Dolron 
 
I will show you fear in a handful of dust II (2016) is a display of a myriad of dust particles, which move against a dark background in extreme tranquility. The dust grains reflect light and shine in different nuances – their movement is detected by high sensory machinery, which is also able to record their sound in a remote undertone. The movement of the particles is looped, mimicking their continuous form. Layered by connotations of beginning and end, the film reflects upon human’s existence, our roots, the passing of time and the intrinsic transience of our nature (Desiree Dolron) 

Museum Dust Composition and Deposition 

Conservators generally strive to remove accumulated dust with the intent to reveal the true nature of an object, to prevent damage, and to mitigate the appearance of neglect. Museum dust contains organic and inorganic particles, natural and synthetic fibers (from clothing, hair, dead skin cells), insects, plant and paper fragments, food, salts, and gaseous pollutants1.  Particles of soot – mainly composed of carbon derived from the combustion of fuels used for heating and transportation – can form a dark, greasy deposit on object surfaces where sufficient air filtration is lacking. On feathers, these deposits can be highly resistant to cleaning.   

Larger dry particulates such as the fibers shed from visitors’ clothing (cotton, wool and by mid-twentieth century, increasingly synthetic materials) can cause a reduction in gloss, and obscure color and pattern. Dust from mineral sources can be abrasive and get trapped in between the fine structure of barbs and barbules. In humid environments, calcium-rich deposits can eventually solidify into accretions on the feather surface or become ingrained, complicating their removal.2 Organic matter deposited on a feather tends to attract water, making the feather more hygroscopic and causing localized RH shifts, while feeding biological growth. Accumulated dust can also result in a loss of appreciation for the object, which increases the likelihood that it will be hidden away in storage, or even disposed of and replaced. 

Cleaning campaigns may be guided by preservation concerns, as well as by an idea of what the object should look like. Primarily, conservators attempt to remove or reduce visible layers of dust associated with a specific period in the object’s life. Some dust may be acceptable as historic patina, but the threshold of what is acceptable varies across historic periods and cultures.  

Dry dirt – layer of loose particulates of museum dust on bird taxidermy (Great Tinamou in the American Tropical Rainforest diorama at AMNH) obscuring color and gloss.  ©AMNH/M.Paulson 
Dry dirt – layer of loose particulates of museum dust on bird taxidermy (Golden-collared Manakin in the American Tropical Rainforest diorama at AMNH) obscuring color and gloss.  ©AMNH/M.Paulson 
Snowy Egret taxidermy 
Sooty black carbon deposition ©AMNH/R.Riedler
Scrub Jay taxidermy
Paint stain & dry dust with high fiber content ©AMNH/J.Hughes, R.Riedler

AMNH Feather Conservation Survey 

In our survey, we asked our colleagues about their most common goals in carrying out a cleaning treatment. For 82 survey respondents (88.17%), the removal of loose particulates was the highest priority, followed by the removal of stains (38.64%) and the removal of oily soiling (35.87%).  

Standardized Dust and Soil  

To better understand the impact of cleaning materials and techniques on the preservation of dirty feathers, we needed to generate some realistic samples for testing. That is, we had to replicate the loose particulate deposits and oily soiling that happens on real-world bird taxidermy using sample feathers, balancing what is realistic with what is reproducible. (We decided not to address “stains” like blood, preen oil, etc. as they often require a case-by-case approach to treatment.) Then we can describe in detail how each method is applied to reduce or remove soils, assess the efficacy of those methods on our selected soils, and look closely at feather damage associated with their application. 

Clockwise from the top: Dust-sebum emulsion, AMNH museum dust, ASHRAE #2 (tan), ASHRAE #1 (black), ASHRAE#1:#2 (1:2), ASHRAE #1:#2 (1:3) ©AMNH/R.Riedler

Many before us have approached the challenge of preparing soiled samples for study. Conservators and conservation scientists have applied a broad range of purposefully manufactured dust mixtures to various substrates in order to perform surface cleaning experiments. Examples include UV-fluorescing powders, museum dust (actual dust collected from museum collections), dust collected from exposed outdoor surfaces and standardized test dusts.  

Dry cleaning study 

Acknowledging that there is always going to be variation in dust from different environments, and that any dust that we elect to use in our experimental work will not be a perfect analogue for dust from another source, we decided to use ASHRAE standardized test dusts for our study of dry cleaning techniques. Test dusts are manufactured to meet tight specifications for composition and particle size for the purpose of testing filtration, heating, and air conditioning systems. In composition they are reasonably similar to samples of museum dust that have been collected and analyzed.4 The benefits of this approach are that the dust has a known composition, consistent samples can made from that dust, and that our experimental work will be repeatable by other researchers. 

We tested various mixtures of two different dust standards, ASHRAE #1 (contains carbon) and ASHRAE #2, and settled on a ratio of 1 part ASHRAE #1 to 29 parts ASHRAE #2. The small amount of carbon-containing AHRAE #1 contributed a stubborn, sooty component, and also increased the visibility of the test dust on the feathers, which we felt was important for modeling a realistic cleaning treatment. Below are the ingredients in the mixture.

  • SiO2
  • Al2O3
  • CaO
  • K2O
  • Fe2O3
  • Carbon
  • Cotton linter
  • Na2O
  • MgO
  • TiO2
Test dust ASHRAE #1:#2 (1:29 ratio) applied to a pennaceous Swan feather by shaking the feather in a box of the dirt (soiling gets caught between barbs and barbules and sits on the surface). ©AMNH/M.Paulson 
Test dust ASHRAE #1:#2 (1:29 ratio) applied to a pennaceous Swan feather by sifting dirt onto the feather (soiling mostly sits on the surface with a bit caught between barbs & barbules) ©AMNH/M. Paulson 

Wet cleaning study

We used the same approach to replicate a second oily type of soiling. A variety of standardized soiling recipes have been explored for use in paintings and textile conservation research. Among them is a dust-sebum emulsion that is widely used in detergency testing and testing for the removal of simulated body oil and fingerprints. We selected this standard for use in our study of wet cleaning methods. These are the ingredients.

  • Palmitic, Oleic, Stearic, and Linoleic Acids
  • Triethanolamine (TEA)
  • Coconut Oil
  • Deionized Water
  • Paraffin Wax
  • Synthetic Spermaceti
  • Olive Oil
  • Cholesterol
  • Squalene
  • Particulate matter
Dust-sebum emulsion applied (1-2 passes) to a pennaceous Swan feather. ©AMNH/M.Paulson
Dust-Sebum emulsion applied (>4 passes) to a pennaceous Duck feather. ©AMNH/M.Paulson

Preparing Soiled Samples

For both dry and oily soils, it is important to standardize the application method and amount of soiling visible on our test feathers to ensure that we can make a meaningful comparison of cleaning methods. For our dry soil, this meant placing loose feathers in a box with a measured amount of ASHRAE dust and agitating in a consistent manner. For our oily soil, it meant diluting the emulsion with Gamsol, a petroleum distillate with less than .005% aromatic solvents, and applying the mixture as a fine mist in a fixed number of layers to provide a medium-heavy coating. 

Test dust-sebum emulsion in Gamsol (3:1) sprayed on feathers in increasing layers (left to right) ©AMNH/R.Riedler

Footnotes

1Brimblecombe P., Grossi, C.M. The Identification of Dust in Historic Houses 

2Brimblecombe, Peter, David Thickett, and Young Hun Yoon. “The cementation of coarse dust to indoor surfaces.” Journal of cultural heritage 10.3 (2009): 410-414. 

Recommended Reading

The National Trust (UK) Dust Atlas.  https://nt.global.ssl.fastly.net/documents/the-identification-of-dust-in-historic-houses.pdf  

Douglas, M. Purity and Danger. 1966. An Analysis of the Concepts of Pollution and Taboo, Routledge& K. Paul: London  

Hun Yoon, Y. and Brimblecombe, P. 2001. Dust at Felbrigg Hall. The National Trust. Views 32: pp.31-32 

Lithgow, K. and Brimblecombe, P. 2003. Dust – The visitors’ point of view. The National Trust. Views 39: pp. 47-49 

Lloyd, H. and Brimblecombe, P. 2003.  Focusing on dust. The National Trust. Views 39: pp 49-52 

Nazaroff, W. et al., 1993. Airborne Particles in Museums, J. Paul Getty Trust: Los Angeles https://www.getty.edu/conservation/publications_resources/pdf_publications/pdf/airborne.pdf

Tarnowski, A. L., McNamara, Ch. J., Bearce, K. A. and Mitchell, R. 2007. Sticky microbes and dust on objects in historic houses. Objects Specialty Group Postprints 11:  pp. 11-28 

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