Our conservation work is driven by the date at which the museum scaffolding is scheduled to be de-assembled, in preparation for the museum reopening in early 2014. This limited period of time plays its part in our choices, regarding preparatory research, scientific analysis, decision making and ultimately the conservation treatment.
We are very thankful to national and international fellow conservators and scientists, who have kindly shared their experiences, research and techniques working on similar materials. This generosity has allowed us to streamline our own treatment decisions.
To ensure ethical conservation treatment, a number of issues are given consideration.
Our specimens have been assessed for the risks they may have been exposed to in the past, but also those they may face in the future e.g. through continued display. Treatment must aim not only to address existing damage, but also to best protect the specimens from envisaged risks, where these cannot be eliminated (such as high light exposure and unstable environmental conditions).
Throughout our treatment, we aim to use materials and methods which will prolong the survival of the cetacean specimens and where appropriate offer detection and reversibility of our interventions, should the collection’s values or needs change in the future. Before reaching a final decision on treatment choices, the treatment itself is risk assessed, and potential risk management strategies are put in place.
Treatment aims and objectives
Following condition assessments of our cetacean specimens (see blog entry ‘Not so extra-virgin whale oil’), we composed a list of treatment options. These are placed in a table grouped by priority and likely sequence of treatment, though some actions may overlap.
Evaluation of treatment tests
Given that our first priority is to attempt degreasing of the bone surfaces (removing oil residues and trapped dust), we undertook treatment tests following recommendations from conservators at the University Museum of Bergen (Turner-Walker 2012).
Spot-tests were carried out with both polar and non-polar solvents, whereby a solvent was applied to the bone with a toothbrush, the oil saturated surface gently scrubbed, before residues were wiped off the bone with a woven cloth.
Echoing results achieved in Bergen, we found that non-polar solvents, such as turpentine did not achieve removal of degraded oil residues (since oxidised and cross-linked oil degradation products are thought to be mainly polar) (Turner-Walker 2012). Polar solvents, e.g. ethanol helped to remove the most upper layer of oil stained and dust saturated surface areas, however did not achieve satisfactory reduction in oil degradation residues.
Further recommended testing involved applying a 5%v/v ammonia solution in deionised water to the oily bone surface by the above mentioned method. A process of oil saponification was achieved, producing a soluble soap scum, which could be wiped from the surface. Encouragingly, this method (using a low ammonia percentage) proved to be very effective in reducing the oil degradation products on the whale bone surfaces tested.
In areas where oil soaked dust is engrained in the bone surface (despite vacuuming), we found toothbrush scrubbing the surface initially with ethanol helped to remove engrained surface dust. Followed by treatment with ammonia, the oily scum residues could be wiped off or wet vacuumed away.
Assessing the use of ammonia to degrease bone surfaces
Following successful treatment tests using ammonia, the treatment of choice is assessed, based on its justifiability and associated risks.
Can it be justified?
Given the variety in condition and cartilage preservation of our cetacean skeletons, it is our preference to treat the bone in situ with aqueous ammonia. This allows specific areas to be targeted, (rather than indiscriminately submerging them in a degreasing solution of choice). Visual and pH treatment tests showed limited ammonia application is non-detrimental to the bone, and indicated the method to be efficient in terms of cost, time and ease of use.
What are the risks to the conservators and specimens?
Ammonia is hazardous to humans (corrosive/toxic vapours). To avoid health implications, conservators are to wear protective equipment (including vapour masks) and work in a ventilated space. Exposure periods are interspersed with regular breaks and accidental splash contact areas are rinsed with water (e.g. eye wash station).
The risk of over-wetting the bone is avoided by working in small areas at a time, applying aqueous ammonia by brush (not directly on bone), followed by prompt wiping clean/wet vacuum suction of the worked surface area. The treated area may be further dried by wiping the surface with ethanol.
To try avoid abrasion of the bone surface during treatment, soft bristle toothbrushes or woven wipes are used, allowing pressure to be adjusted. Should detrimental effects be noticed, treatment is to be discontinued in the affected area. Areas of visibly weak or delaminating bone are not to be treated.
The risk of aqueous ammonia (alkali) swelling or weakening cartilage structures, suggests exposure to ammonia in these areas ought to be limited/avoided. Following contact with ammonia, cartilage areas may benefit from wiping with a cloth dampened with a deionised water/ethanol solution to remove alkali residues.
Do keep an eye out for our next conservation blog entry, where we will present our first treatment in progress images!
- 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
Reviewed by Bethany Palumbo, Conservator of Life Sciences