In a previous post, I described some of the issues we’re facing in the treatment of our painted coffin of Tawahibre.
The top of the coffin before treatment – note the large losses and areas where the paint and gesso are just barely hanging on by a (plant fiber) thread
We’ve managed to clean much of the painted surface, but there are many areas of the paint and gesso that are so fragile, you get the feeling that a deep exhale – not to mention a sneeze – would send fragments flying. (And when I say gesso, I’m referring to the calcium carbonate preparatory layer/ground, which has plant fiber inclusions, that I’d like to investigate further).
Such areas require consolidation. We use this word, consolidation, a lot in conservation, and many of our treatments involve this process. Consolidation is essentially the reunification/reinforcement of a weak or powdery substance through the application of a material that we refer to as a consolidant. Consolidants often consist of dilute adhesive solutions, and they may be applied directly to artifacts with a brush or syringe, by spraying onto the surface, and in some instances, it may be appropriate to immerse an artifact in a consolidant solution. Ideally, a good consolidant must be stable (good aging properties), reversible (can be removed if necessary), and should not change the appearance of the artifact.
We have mixed up a variety of consolidant solutions to have on hand in the Artifact Lab – here are a few, along with some brushes, a plastic pipette, and syringes
Choosing an appropriate consolidant requires testing ahead of time. To start, it is important to test a variety of solvents (such as water, acetone, ethanol) – knowing which solvents can be used safely on a particular artifact will likely narrow down the range of adhesives that can be used (due to the fact that many adhesives are only soluble in a select number of solvents). In the case of our painted coffin, this involved testing all of the colors of the painted surface as well as the gesso substrate. Testing was carried out by rolling a swab dampened with each solvent over a discreet area and then observing the area for changes.
Solvent testing on an area of blue paint
After carrying out these tests, I did some research into what other conservators have used successfully for similar treatments on similar artifacts. In our field, we are fortunate to have a good body of published literature, and there is increasingly more information that can be found on the web as well. The sources I referred to included articles in the Journal of the American Institute for Conservation (JAIC), and a variety of books that have been published on the subject of conservation of Egyptian collections. Websites/blogs that I have found really useful include Inside the Conservator’s Art: A behind-the-scenes look at conserving Egyptian artifacts at the Phoebe A. Hearst Museum of Anthropology, conservator’s entries on the Brooklyn Museum blog, and the British Museum’s online collections database, which has many records with detailed conservation treatment information. There are actually lots of great blogs and websites out there, and I am grateful to my colleagues for actively sharing information in this way.
After this work, I selected several consolidants, and conducted another round of testing. During my testing I discovered that water was the key to getting the paint and the gesso to relax. Unfortunately, the painted surface is sensitive to water, but I found that a 50:50 mixture of water and ethanol is acceptable for use, especially when applied in a solution behind the lifting paint. In the end, we’ve chosen to consolidate the very fragile paint with a solution of methyl cellulose (a water-soluble cellulose ether) in a 50:50 water/ethanol mixture. To re-adhere larger flakes and chunks of gesso, we are experimenting using higher concentrations of methyl cellulose alone, and in combination with other adhesives, including Lascaux, a water-based acrylic resin.
An area near the foot of the coffin, before (left) and after (right) readhering detached gesso and consolidating paint
As I’ve stated before, this will be an ongoing project in the Artifact Lab – we will continue to report on our treatment progress, and any interesting discoveries made along the way (which is inevitable!).