The Conservation of Poedua: Part 4

The Conservation of Poedua: Part 4

Now that we have cleaned the back of the canvas we can look at surface cleaning the front of the painting.  This is a separate procedure from the removal of varnish and overpaints and is completed first because surface dirt is the first layer encountered.  The reason we remove the dirt layer on paintings is because it considerably alters the colour and tone of original paint, can obscure image detail and significantly alter the surface gloss, clarity and hue of surface coatings.

Surface Cleaning
Detail; 1992-0035-1883; Lake Manapouri; Baker, William George; During treatment. The cleaned rectangular area at the left shows you what a difference surface cleaning makes to the appearance of a painting, 2006. Photograph by Katherine Campbell © Te Papa
Surface dirt is a mixture of all sorts of quite unpleasant things including flakes of skin and hair, smoke from household fires and tar from cigarettes, food and drink deposits, moulds and fungi, insect debris and general atmospheric pollutants!  To remove the surface dirt, it is necessary to overcome the bonds that are holding the dirt to the painting without disrupting the underlying paint layer.  To find the safest cleaning formulation we carry out a process of testing different mixtures through careful application and monitoring of the results.
Testing notes
As we go through the testing process to find the best cleaning formulation, we keep a detailed written record of what we used and how well it worked, 2011. Photograph by Katherine Campbell. © Te Papa

When we carry out our testing, we apply the cleaning solutions with small cotton swabs in a rolling motion over the paint surface.  We test inconspicuous areas first, starting with light colours and then progress to all the main paint colours.  We keep and label the test swabs for comparison.  We often have to reassess our cleaning strategy because the solubility of dirt and paint can change across the surface of the painting requiring the use of different materials and concentrations of solutions. The most common surface cleaning agents are aqueous in nature – meaning they are water-based.  We can modify and control the properties of the water by adding pH buffers and ionic buffers and by adding chelating agents, surfactants, enzymes and gelling agents.

Mel mixing
Mel carefully makes up a testing solution to trial on the painting, 2011. Photograph by Katherine Campbell. © Te Papa

Last year I was able to attend a course in Melbourne about the cleaning of paintings using the Modular Cleaning Program.  This is a database system and an approach for cleaning paintings that has been developed to help conservators use established theory and materials in a way which makes the complicated chemistry of cleaning more accessible.  Basically, the computer program is better at working with piles of numbers than us!  It saves us time by working out the complicated stuff, like ionic equilibria, which requires pages of calculations and is really boring and not to mention, tough!

With the help of the modular cleaning program, we are able to make up and test a wider range of formulations than we would ordinarily have time to do, 2011. Photograph by Mel Carlisle. © Te Papa

Through our testing and the help of the Modular Cleaning Program, we arrived at a solution containing a mixture of enzymes which we will use to safely and effectively surface clean Poedua.  The next blog post will talk about the surface cleaning process now that we have found our cleaning agent and will include some nice images of the cleaning in progress.

spliced image
Once a suitable cleaning formulation has been found, all the paint colours utilised in the composition are tested to make sure of its suitability.  The small circular areas are the cleaned test patches, 2011. Photograph by Katherine Campbell © Te Papa


  1. Stay tuned for this weeks post which will be all about the actual surface cleaning and the result!

  2. I’ve really enjoyed reading up to this point. Great to get the real dirt(!) on a conservation treatment. Looking forward to future installments…

  3. Hi Katherine, excellent blog – amazing process

  4. Very interesting to see that a New-Zealander is doing restauration (french spelling) of a Princess from Tahiti. Congratulations Katherine !

  5. I enjoyed this well written and carefully argued blog. All the best with the cleaning of this important painting.

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