‘Thou art as a whale…’

Nicola Fielding has been up close with our whales to produce smart line drawings.
We may annotate these for our conservation records.

Fin Whale

Minke Whale (Balaenoptera acutorostrata Lacépède, 1804) (http://nicolafieldingdrawings.wordpress.com/)

Jonathan Delafield Cook recently exhibited charcoal drawings inspired by the research and travels of Charles Darwin at Purdy Hicks Gallery. The exhibition included a LARGE scale Sperm whale!

Sperm Whale (physeter macrocephalus)

Sperm Whale (Physeter macrocephalus Linnaeus, 1758), (http://www.fadwebsite.com)

Watch this space for more whale art posts…

Gemma Aboe, Assistant Conservator

 

Not so- extra virgin whale oil

Mechanical and chemical deterioration
Having familiarised ourselves with the composition of whale bone and oil, this blog entry allows us explore the deterioration of the various natural materials found on our cetacean specimens. This will aid accurate condition assessing (see images) and facilitate targeted conservation treatment.

Rain drop stains on Bottlenose whale (Hyperoodon ampullatus)

Water stains on Northern Bottlenose Whale rib (Hyperoodon ampullatus (Forster, 1770))

Deterioration of whale bone
Bone is sensitive to environmental factors. Being hygroscopic, bone will absorb and release moisture with relative humidity fluctuations in the museum, (which due to the leaky roof have been in constant fluctuation).
Excess moisture may cause hydrolysis of the protein’s peptide linkages, causing swelling and structural weakening (due to a reduction in molecular weight) (Cassman et. al 2008). Moisture may also promote mould and micro-organism development, capable of degrading hydroxyapatite (a calcium phosphate mineral), through the release of acids.
Extreme dryness may lead to shrinkage of the bone, causing warping, cracking and delamination (O’Connor 2008).

Bone delamination on Killer whale cranium (Orcinus Orca)

Bone delamination on Killer Whale cranium (Orcinus orca (Linneaus, 1758))

Variations in temperature also impact the stability of the bone, with excess heat leading to the destruction of protein and loss of moisture, while the combination of heat and moisture may damage the ossein (collagen forming organic matrix).

Areas of loss on protein rich Killer whale phalanges (Orcinus Orca)

Areas of loss on protein rich Killer Whale phalanges (Orcinus orca (Linnaeus, 1758))

Bone is also light sensitive, thus exposure to visible and UV light (e.g. through the glass roof), will over time cause bleaching through oxidation. UV light also affects exposed proteins, e.g. comprising the skin (on phalanges), causing yellowing and friability, due to chain scissions.

Deterioration of whale oils
Oils are composed of triglycerides (esters of glycerol and long chain fatty acids). There are three main mechanisms by which oils chemically decompose or ‘rancidify’ (a term used for edible oils/fats): hydrolysis, bacterial action and oxidation.

Oil drips on chevron of Bottlenose whale (Hyperoodon ampullatus)

Oil drips on chevron of Northern Bottlenose whale (Hyperoodon ampullatus (Forster, 1770))

a) Hydrolysis: occurs when the oil’s ester groups are broken down by water (such as high humidity), or catalytic amounts of mineral acids*, into their component glycerol backbone and free fatty acid chains (Mills and White 1999). The process can lead to an alteration in the oil’s viscosity, colour and odour, such as when volatile carboxylic acid is released. Hydrolysed oil products form polar bonds with the whale bone tissue (hydroxyapatite), and can be seen as drips absorbed on the bone surface. It is thought the higher the free fatty acid content in whale oil, the darker the oil, ranging from pale yellow to dark brown (Turner-Walker, 2012).

b) Bacterial action: includes bacteria and lipase (enzymes), which catalyse the breakdown (of ester bonds) or the hydrolysis of lipids (oils). *Micro-organisms causing acid dissolution of bone mineral, may further lead to free fatty acids forming insoluble salts with calcium in/on the whale bone.

c) Oxidation: occurs when oil is exposed to oxygen in the air, initiating a free radical process, leading to cross-linked films and/or bond breaking (particularly in unsaturated fatty acids with reactive double bonds) and the formation of degradation products (Miller 2013; Mills and White 1999).

Oxidation degradation products include hydroperoxides, free fatty acids, pungent carbonyls, aldehydes and volatile carbolic acid (phenol).
Cross-linking of oil compounds to form a rubbery solid, occurs when bonds form between neighbouring fatty acid chains via a free-radical process, to form a polymer network, characteristic of a ‘dried’ oil film (Gorkum 2005). The blackening of fatty areas is due to oxidation being an exothermic reaction, i.e. they burn.

Blackened oil compounds on Killer whale ribcage (Orcinus Orca)

Blackened oil compounds on Killer Whale ribcage (Orcinus orca (Linnaeus, 1758))

The rate at which oxidation of oil occurs, depends on the availability of oxygen, light, temperature and humidity as well as any transition metals, all of which may act as pro-oxidants (Miller 2013).

The adsorption of atmospheric oxygen in whale oil, and the desorption of (volatile), low molecular weight degradation products, causes weight and volume fluctuations in oil-soaked bones and surface films, potentially weakening the bone structure (Turner-Walker 2012).

Un-oxidised oil in the bulk of whale bones may wick to the surface via capillary action through the bone’s porous structure, allowing a thick, sticky, fully-oxidised oil film to accumulate on the bone surface. The exposed oil along with its acidic degradation products may not only attract dust, but also dissolve the bone mineral hydroxyapatite, reducing the bone rigidity.

Oil soaked and dust covered spinous processes on Lesserfin whale (Balaenoptera physalus)

Oil soaked and dust covered spinous processes on Minke Whale (Balaenoptera acutorostrata Lacépède, 1804)

Once an oil film has hardened, oxygen diffusion and the resulting degradation process slows, sealing in un-oxidised and partially oxidised oil reserves (Turner-Walker 2012).
Can you predict our conservation dilemmas to come?

Further readings:

  • Cassman, V. et. Al (eds). 2008. Human remains: Guide for museums and academic institutions. Lanham: AltaMira Press
  • Miller, M. 2013. Oxidation of food grade oils. Available at: http://www.oilsfats.org.nz/Oxidation%20101.pdf. Accessed: 11/06/2013
  • O’Connor, T. 2008. The archaeology of animal bones. Texas: Texas A&M University Press
  • Turner-Walker, G. 2012. The removal of fatty residues from a collection of historic whale skeletons in Bergen: An aqueous approach to degreasing. In proceedings of: La conservation des squelettes gras: méthodes de dégraissage, At Nantes, France

Gemma Aboe, Assistant Conservator

Down to the bone

Research on material type
Prior to carrying out a detailed condition report of the cetacean skeletons, it is useful to have an understanding of the materials we are likely to encounter, in terms of structure and chemistry. This blog entry invites you to join us in learning about the composition of whale bone and oil.

Whale bone
(Cetacean) bone is comprised of a composite structure of both an inorganic matrix of mainly hydroxylapatite (a calcium phosphate mineral), providing strength and rigidity, as well as an organic protein ‘scaffolding’ of mainly collagen, facilitating growth and repair (O’Connor 2008, CCI 2010). Collagen is also the structural protein component in cartilage between the whale vertebrae and attached to the fins of both the Killer Whale and the Dolphin.

Bottlenose whale spinous processes, with visible break healed during life

Northern Bottlenose Whale (Hyperoodon ampullatus (Forster, 1770)) spinous processes, with visible break healed during life

Cartilage on Bottlenose dolphin pectoral fin

Cartilage on Bottlenose Dolphin (Tursiops truncatus (Montagu, 1821)) pectoral fin

Relative proportions in the bone composition (affecting density), are linked with the feeding habits and mechanical stresses typically endured by bones of particular whale types. A Sperm Whale (Physeter macrocephalus Linnaeus, 1758) skeleton (toothed) thus has a higher mineral value (~67%) than a Fin Whale (Balaenoptera physalus Linnaeus, 1758) (baleen) (~60%) (Turner Walker 2012).

Compact bone and spongy (cancellous) bone

Compact bone and spongy (cancellous) bone

The internal structure of bone can be divided into compact and cancellous bone. In whales, load-bearing structures such as mandibles and upper limb bones (e.g. humerus, sternum) are largely composed of compact bone (Turner Walker 2012). This consists of lamella concentrically deposited around the longitudinal axis and is permeated by fluid carrying channels (O’Connor 2008). Cancellous (spongy) bone, with a highly porous angular network of trabeculae, is less stiff and thus found in whale ribs and vertebrae (Turner Walker 2012).

Oil soaked sternum on Killer whale

Oil soaked sternum on Killer Whale (Orcinus orca (Linnaeus, 1758))

Whale oil
Whales not only carry a thick layer of fat (blubber) in the soft tissue of their body for heat insulation and as a food store while they are alive, but also hold large oil (lipid) reserves in their porous bones. Following maceration of the whale skeleton after death to remove the soft tissue, the bones retain a high lipid content (Higgs et. al 2010). Particularly bones with a spongy (porous) structure have a high capacity to hold oil-rich marrow.

Comparative data of various whale species suggests the skull, particularly the cranium and mandible bones are particularly oil rich.

Bottlenose Dolphin (Tursiops truncatus, Montagu, 1821) illustration showing typical oil-rich regions (adapted from Nicola Fielding 2013)

Bottlenose Dolphin illustration showing typical oil-rich regions (adapted from Nicola Fielding 2012)

Along the vertebral column, the lipid content is reduced, particularly in the thoracic vertebrae (~10-25%), yet greatly increases from the lumbar to the caudal vertebrae (~40-55%). The chest area (scapula, sternum and ribs) show a mid-range lipid content (~15-30%), with vertically orientated ribs being more heavily soaked lower down (Turner Walker 2012, Higgs et. al 2010).

Killer whale ribs soaked with oil, attracting dust

Killer Whale (Orcinus Orca (Linnaeus, 1758)) ribs soaked with oil, attracting dust

Whale oil is largely composed of triglycerides (molecules of fatty acids attached to a glycerol molecule). In Arctic whales a higher proportion of unsaturated, versus saturated fatty acids make up the lipid. Unsaturated fatty acids (with double or triple carbon bonds causing chain kinks, preventing close packing (solidifying) of molecules), are more likely to be liquid (oil), versus solid (fat) at room temperature (Smith and March 2007).

Close up of Humpback whale upper mandible with oil ‘pool’

Close up of Humpback Whale (Megaptera novaeangliae (Borowski, 1781)) upper mandible ventral side with oil ‘pool’

Please look out for our next blog entry, which will look at how cetacean bone and oil degrade. Can you imagine the treatment consequences?

Further readings:

  • Conservation Resource Centre (CCI). 2010. Care of ivory, bone, horn and antler. Available at: http://www.cci-icc.gc.ca/publications/notes/6-1-eng.aspx [Accessed: 3/6/2013]
  • Higgs, N.D. et.al. 2010. Bones as biofuel: a review of whale bone composition with implications for deep-sea biology and palaeoanthropology. In: Proceedings of the Royal Society B: Biological Sciences
  • O’Connor, T. 2008. The archaeology of animal bones. Texas: Texas A&M University Press.
  • Smith, M. B. and March, J. 2007. Advanced organic chemistry: Reactions, mechanisms, and structure (6th ed.), New York: Wiley-Interscience
  • Turner-Walker, G. 2012. The removal of fatty residues from a collection of historic whale skeletons in Bergen: An aqueous approach to degreasing. In proceedings of: La conservation des squelettes gras: méthodes de dégraissage, At Nantes, France

Gemma Aboe, Assistant Conservator