Pascarella's Puzzle: The chemical approach to ancient art restoration

To discover pieces of art such as Pascarella’s is like uncovering a piece of history. The papers, so yellow and brittle, take you back to the early 1900s, where only the privileged had the time and resources to paint images like the one seen below. The watercolors, so eloquently put together, just seems to flow with shadings, creating a soft image that makes you wonder. Upon discovery, you would treat the pieces like an antique because it seems like anything you do could alter the condition of this prized possession. But, as chemists we can’t appreciate the art until we’ve done anything and everything in our power to try and restore it. Let’s take a look.

Marina Bicchiera and her teams of researchers began by examining Pascarella’s pieces and determined it showed signs of chemical instability. The paper manufactured during Pascarella’s time was composed mostly of cellulose that when exposed to hydrolytic and oxidative conditions would degrade and de-polymerize. Over the years, aging and direct exposure to sunlight caused these images become brittle, fragmented, and severely yellowed, signs of acidification and oxidation. So the mission was to reverse the damage by spraying the paintings with a solution that would restore their chemical stability. In order to do this, they proposed a restoration method that would simultaneously de-acidify and reduce the images. To ensure this process would not damage the composition of the paper or interact with the painted images, they proposed using an ethanol solution composed of 3.0g/l calcium propionate and 6.0g/l of borane tert-butylamine complex. They tested the applicability of their deacidification/reduction solution on more than 1,000 original pieces and found no adverse or damaging affects on the work. 

But, before they did any work on Pascarella’s pieces, they had to create a comprehensive map of the paintings. They used a combination of techniques including XRF, Raman/Infrared spectroscopy, and SEM/EDS to determine important information about the composition of the paintings and if this would be affected by the proposed restoration process. Using these techniques in combination with each other, they were specifically able to determine:

-pigment composition
-impurities in the paper
-% elemental composition of pigments
-structurally different carbon based materials
-mixed pigments masked by presence of cellulose
-binding material of cellulose paper
-vibrational modes of carbonyl groups found in the paper, before and after redox
-overlapping pigment layers, unique to topography and artisanal technique

The results were indeed comprehensive but highlighted a few very important pieces of information. None of the organic dyes used in the paintings would be affected by chemical restoration, except for chrome yellow. Due to its reactive nature, it has the potential to change after the restoration process, which could then alter the entire image. So, the team decided to test a 1940 sample of lead chromate with the solution and found that it did not change when sprayed with the deacidification/reduction solution. They, then, proceeded with the restoration process by spraying Pascarella’s pieces and allowing them to dry. They found that, after treatment, the yellowing was removed and some colors were enhanced. The stability and durability of the paper increased and allowed for the complete restructuring of the work.

Some fragments that were not used in the restoration was analyzed by SEM, and found to consist of material specific to geographical regions. A closer look, and these geographical regions were the same regions Pascarella traveled. This, in addition to other evidence, strongly suggests that Pascarella used local materials in his work. When painting his images, he used materials that were readily available in the region he was traveling. Most of the pigments used in his Indian drawings were composed of unique material like martite and weddellite that were prevalent in that area. 

This is not something any one of these techniques would ever explicitly tell us. The results of the tests, used in combination with each other, were like pieces of a puzzle put together to solve and underlying and perhaps unexpected bigger picture. That’s analytical chemistry at it’s finest.