Before & After Gallery
Solvent Extraction of Oil from a Whale Bone Sculpture
This sculpture was carved from the mandible of a bow head whale by the Inuit artist Henry Evaluardjuk in 1968. Unfortunately, circumstances dictated using fresh bone which still contained a great deal of the oil and fat which characterize this family of marine mammals. This choice resulted in a continual oozing of oil from the surface of the sculpture and an unpleasant odour as a fraction of the exudate became rancid on exposure to the atmosphere. Analysis of samples of the oil revealed that it was unlikely to dry out and that the bone would therefore continue to ooze oil for a long time to come. It was decided that complete extraction of the oil by solvent would be necessary to clean the bone and prevent a recurrence of this problem. It was understood that the surface colour of the bone would probably not be altered by this process; dark areas where the spongy, inner bone had been exposed during carving, and areas where the dark, outer surface remained would not be visibly lightened. As these contrasting areas contributed to the sculpture quality of the piece this was considered advantageous.
Solvent extraction of oils and greases from bones (primarily for natural history specimens) has been traditionally carried out with large quantities of volatile solvents. This is expensive and also hazardous to the health of operators. For the treatments of the Evaluardjuk sculpture a variation on this method was devised where the solvent trichloroethane was enclosed in a close-fitting polyethylene bag surrounded by a water jacket. Thus, a much smaller volume of solvent was used and losses and health hazards due to evaporation were minimised. Such a small volume of solvent became quickly contaminated with the extracted oil so, rather than discard it, it was purified by distillation and returned to the bag.
Figure 1.
Figure 2.
Extraction
The apparatus shown in Figures 2 and 3 was constructed. The input and output pipes were arranged so that solvent would flow from one end of the enclosure to the other. The output pipe to the pump was at the lowest point of the bag. After mechanical cleaning to remove dried connective tissue from the interior, the sculpture was sealed into a double-layered polyethylene bag and laid in the tank on Ethafoam blocks carved to shape. The bag was connected to the solvent output and input pipes and the water jacked filled, causing the bag to be pressed evenly against the surface of the sculpture. Fifteen litres of trichloromethane were run into the bag and left overnight. After this initial soaking the solvent appeared a dark brown colour. Distillation was begun using the apparatus shown in Figure 3 and the purified solvent run back into the bag. A mercury switch connected to a float in the distillation flask caused the pump and heater to operate alternately, making the distillation an automatic process. Losses due to evaporation were occasionally made up with fresh solvent. The process of extraction of the oil was judged to be complete after 12 weeks when the solvent appeared almost clear. At this point all the solvent was drained from the bag and the sculpture removed. The rancid smell was greatly decreased and the areas which had been black and sticky were much lighter in colour. Once the solvent had dried out the sculpture was prepared for mounting.
Mounting
The sculpture was mounted on a base formed from a filled epoxy resin laid over a steel plate as shown in Figure 4. A padded steel rod was attached to the base and inserted into the hollow interior of the bone. This heavy base and interior rod provided rigid support and also gave enough mass to prevent toppling. The visible parts of the base were veneered in a dark wood varnished to match the decor of the display gallery.
2. Column
3. Mercury switch
4. Float
5. Flask
6. Relay
7. 12 Vdc
8. 110 Vac
9. Heater
12. Pompe
13. Joint étanche
14. Sculpture
15. Sac en polyéthylène
16. Tuyau d'évacuation
17. Enveloppe remplie d'eau
18. Cuve doublée de polyéthylène
19. Blocs en Ethafoam
