42nd Annual Meeting, Objects Session, May 31, Pine Pitch: New Treatment Protocols for a Brittle and Crumbly Conservation Problem by Nancy Odegaard, et al.

In this paper presented at Saturday’s Objects Session, Nancy Odegaard, Marilen Pool and Christina Bisulca described a new treatment protocol they established, along with their colleagues Brunella Santarelli, Madeleine Neiman, and Gina Watkinson, for treating baskets with deteriorated, pine pitch coatings.  The treatment protocol was devised after conducting a survey of the basket collection at Arizona State Museum, where the majority of the pitch-coated ethnographic baskets (70 out of about 100) had unstable, blanched, cracked and brittle surfaces.  The baskets required treatment so that they could be moved to a new location.
The majority of the baskets were Apache and were made using a twining or coiling technique.  The pine pitch, obtained from the piñon pine would have been applied to the surface of the baskets as a waterproofing measure.  Two colors of pitch were observed on the exterior of the baskets, each with different condition issues.  Some baskets were covered with a red pitch that appeared translucent.  The other baskets were covered with a dark brown to black, opaque pitch. Both colors of pitch had suffered degradation due to factors such as UV, temperature and pollutants, however the red pitch appeared more unstable and had a formed a series of fine cracks.  The darker pitch had deeper cracks.
Because the baskets had to be moved, a treatment protocol was established to stabilize the surfaces so the baskets could be safely transported to a new storage area. Previous treatments for deteriorated pitch had included consolidation with solvents or the use of heat (using a butane torch!) to reintegrate the cracked, crumbly surface.  The ASM team was looking for another treatment option, and one that took into consideration the vast numbers of objects that required treatment.  Borrowing from methods used to clean aged varnish in the field of paintings conservation, the conservators decided to reactivate the pitch using a solvent to stabilize the flaking material and reattach the crumbly surfaces.
Prior to any treatment, the conservators wanted to get a cultural perspective on the treatment since they did not want to add material, alter the pitch or appearance of the basket and wanted to make sure the objected retain their cultural integrity and significance. Nancy consulted with a Navajo weaver who said that pitch baskets should always look shiny and therefore reactivating the pitch, and the subsequent shiny appearance the material would take, was acceptable.
Because of the success in the use of ethanol in cleaning aged, pine-based varnish from paintings, that was the solvent chosen for the reactivation of the pine pitch on the ethnographic baskets.

  • The first stage of the treatment was to place the baskets (many supported by foam rings or, if they fit, by large glass beakers) in an ethanol solvent chamber for 24 hours.  This would condition the surface and prepare it for further treatment.
  • The baskets were then removed from the solvent chamber and areas of the surface sprayed with ethanol using a Dahlia sprayer for a more direct application of the solvent.
  • Brushes, foam swabs wrapped in PTFE (Teflon) tape and Kim Wipes (lint-free wipes) soaked in ethanol were then used to relocate any loose flakes.
  • After one side was treated, the pitch was left to air dry for a few hours, then the basket was turned and the other side sprayed with ethanol and flakes reattached.
  • When the entire pitch surface had been treated, the basket was left to air dry for about 24 hours or until the pitch no longer felt tacky.

During treatment the conservators noticed that the transparent red pitch reacted faster to the ethanol.  The darker pitch was less soluble and more pressure was needed to re-adhere fragments.  They also noticed that for areas with damaged basketry elements, the reactivated pitch served to reinforce those areas of the plant fiber so that no further stabilization of those woven elements were required.
Analytical Investigations
In addition to the treatment, instrumental analysis was conducted to characterize the two types of pitch and determine if there were any changes in the pitch before and after treatment.  The analysis was conducted using Fourier Transform Infrared Spectroscopy (FTIR) and optical microscopy.
The first investigations looked at the two types of pitch and whether there were any changes observed before and after treatment.  Analysis showed that there were no differences before and after treatment and therefore reactivation and exposure to ethanol did not alter the material chemically.  There were differences, however, noted between the red and dark pine pitch. The transparent red pitch had a low aromatic component as opposed to the dark brown-black material, which had a high aromatic hydrocarbon content.
A series of experiments were then conducted in order to figure out what accounts for these differences and it turns out it has to due with how clean the pine pitch is and at what temperature it was initially heated to during application.  Using optical microscopy, the dark pitch seemed to contain woody materials and had inclusions of bark.  Could this be the explanation for the differences in the aromatic content?
Samples of resin from piñon pines in the Navajo area were collected and heated to different temperatures and then examined using microscopy as well as FTIR.  It turns out that if the pitch is clean and does not contain any woody components, there are little to no aromatics.  However, when bark is present in the pitch, the aromatic content is similar to that seen on the pitch coating the ethnographic baskets.  The heating temperature also plays a role not only in the color, and a temperature of 180° C produces pitch similar to that seen on the ASM baskets.
This was a really informative talk describing a new approach to not only the treatment of crumbly pine pitch, but also a protocol for treating large numbers of unstable baskets.  The talk was of particular interest to me because some close colleagues and I have often encountered similar types of condition issues with different resinous materials on archaeological objects (for example bitumen coatings on ceramics, bitumen or pitch on baskets, natural resins on Egyptian funerary objects and mummies) and have often discussed the need for approaches to the stabilization of these materials other than consolidation using synthetic resins.   The literature is a bit lacking in terms of the treatment of these types of materials and it’s wonderful that Nancy and her team at ASM are adding to this body of information by sharing their treatment methods and findings (and hopefully publishing them in the OSG Postprints or another publication!).
The next stage of the pine pitch/basketry project will be to work on the archaeological basketry collection and I looked forward to hearing about their approaches to the stabilization of pitch on those artifacts.