ALVAR AND BUTVAR: THE USE OF POLYVINYL ACETAL RESINS FOR THE TREATMENT OF THE WOODEN ARTIFACTS FROM GORDION, TURKEY
KRYSIA E. SPIRYDOWICZ, ELIZABETH SIMPSON, ROBERT A. BLANCHETTE, ARNO P. SCHNIEWIND, MAURAY K. TOUTLOFF, & ALISON MURRAY
3 USE OF ALVAR AND BUTVAR ON THE WOODEN ARTIFACTS FROM GORDION
At the time of excavation, the state of preservation of the wooden objects from Gordion varied from excellent (e.g., boxwood serving stand, Tumulus P) to poor (e.g., walnut tops of the plain tables, Tumulus MM). This range was due to a complex interaction of factors, including the inherent resistance to decay of the individual wood species used, the state of preservation of the log tombs (e.g., the structure in Tumulus MM was intact and standing when it was discovered, whereas the tomb in Tumulus P had collapsed earlier in its history), the position of the objects in the tombs, and whether the objects had been affected by water. Young's use of a water-cooled drilling rig in the initial exploration of Tumulus MM had caused a significant amount of water to enter the tomb (Young 1957). In addition, Blanchette attributed the development of soft rot in the log coffin from Tumulus MM to the earlier presence of water in the tomb, possibly at the time of its completion (Blanchette and Simpson 1992).
The fragile state of many of the wooden objects when discovered led the archaeologist Rodney Young to seek advice on preservation techniques. While a few of the most important pieces, including the inlaid table and two inlaid serving stands from Tumulus MM, were treated by immersion in a bath of wax dissolved in gasoline, most of the furniture was coated with a dilute solution of Alvar, a polyvinyl acetal resin, dissolved in acetone (Spirydowicz 1996; Simpson and Spirydowicz 1999) (fig. 2). Young's field notebooks revealed that members of the field crew as well as the excavation foreman were assigned the task of “painting” the wood with an Alvar solution, an activity that no doubt resulted in many treatment variables (Young 1957). Young made it clear that this method was employed primarily as a first-aid measure so that the pieces could be removed safely from the royal tombs.
When the wood was reexamined in 1981, many of the pieces previously coated with Alvar were found to be in a fragile state (Simpson and Spirydowicz 1999). In most cases, it appeared that the solution of Alvar had not penetrated much below the surface, so there was little strengthening effect. When the three-legged banquet tables found in Tumulus MM were examined, the only evidence for a previously applied coating was the presence of whitish or grayish patches on the deteriorated surfaces of the walnut tops, possibly due to application of Alvar while the wood was still damp. However, on some pieces, such as the serving stand from Tumulus W, the Alvar coating was clearly evident and, as such, had helped to preserve an essential decorative feature of the piece. Due to the thickness of the Alvar layer, the bronze studs decorating the front face of this remarkable piece of furniture were still in situ when the fragments were recovered after many years of storage in the depot at Gordion. Similarly, fragments of the mosaic table from Tumulus P still retained most of their pieces of inlay due to the Alvar coating applied by Young's team (fig. 3). It is also worth noting in both cases that the Alvar coating was still clear and colorless approximately 30 years after application.
Fragment of the mosaic table from Tumulus P with thick Alvar coating, prior to surface cleaning
As pieces were prepared for treatment, the previously applied Alvar coatings had to be removed. In most cases, this proved to be an easy task, as the Alvar was readily soluble in acetone. Removal of the thick film applied to the face of the serving stand from Tumulus W was facilitated by the application of gel poultices consisting of Klucel HF in ethanol or an ethanol-acetone mixture. Surface cleaning of the serving stand from Tumulus W provided clear evidence of the continuing solubility of Alvar over time. Other pieces of furniture had been treated with more dilute solutions of Alvar. In such cases, it was more difficult to detect whether the resin was removed from the surface by the cleaning process. However, it is likely that any further traces of Alvar would have dissolved in the solvents used during the subsequent consolidation process. Although the manufacture of Alvar by Shawinigan Products Corporation was discontinued many years ago, in hindsight, the choice of this resin was fortuitous, based on these observations of its behavior over time.
In 1982, Payton consolidated small, unprovenanced cubes of wood from the Gordion tumuli with a 5% w/v solution of Butvar B-98 in equal parts of ethanol and toluene. The wood samples were immersed in the solution and allowed to absorb the consolidant. When the wood sank or floated just below the surface, indicating that most of the air in the wood had been replaced by the consolidant solution, the samples were removed and air-dried.
Measurements taken before and after drying indicated virtually no shrinkage. This finding agreed with the results previously obtained by Barclay, who, in fact, found a minimal amount of expansion in test samples. In comparing treated and untreated portions of samples, Payton found that there was little color change. This result was considered desirable for treatment of those pieces of furniture containing inlay where color contrast between woods was an important feature of the overall design. Payton judged that a 5% concentration of Butvar B-98 imparted sufficient strength to the degraded wood, and he proceeded with treatment of the inlaid table (Payton 1984a) and the two ornate inlaid serving stands from Tumulus MM (Payton 1984b).
Initially, the consolidation process involved immersion of the fragments in solution with the gradual application of vacuum pressure via a hand vacuum pump to assist penetration of the consolidant into the interior of the wood. The objects treated by Payton were in fairly sound condition, and thus a relatively low percentage of consolidant was effective in strengthening the wood. In subsequent seasons, it became obvious that the more degraded pieces, in particular the furniture and wooden objects from Tumulus P, required a higher ratio of consolidant to solvents. In 1991, a second set of consolidation tests was carried out. Small unprovenanced samples of Gordion wood were consolidated in varying concentrations of Butvar B-98 (10, 12.5, and 15% w/v in 60:40 ethanol and toluene). As a result of these tests and the scientific studies detailed below, the original consolidation procedure was modified and refined to successfully treat all of the remaining pieces of furniture (Simpson and Spirydowicz 1999).