Reviving 15th century saints: how our conservator cleaned an oil on panel with an innovative solution

Oil paintings are made up of several layers, often these cannot be seen by the untrained eye but nevertheless disturb the original intention of the artist. Surface contamination, discoloured and darkened varnish and the historic build-up within crevices can all make a remarkable visual difference when they are sensitively removed. Historic oil paintings may have become hidden under various levels of dirt and deterioration in the centuries since their creation, making the cleaning process a complex and scientific task.

Depending on the sensitivity of the paint layer, surface cleaning and varnish removal may at some stage be limited by a conservator to ensure the pigments are not disturbed. However, brilliant new techniques – as seen in Stavroudis’ Modular Cleaning Programme workshop that we hosted in September 2022 – can assist conservators in more thoroughly removing discolouration and contaminants without harming the artist’s brushstrokes. 

Above: numerous solutions were tested during our recent Modular Cleaning Program workshop

Our studio recently restored a 15th century oil on panel that had various layers of discolouration including embedded remnants from old varnish. This unique painting was small but lively in its composition, producing a scene that dramatically combines the stories of St Francis of Assisi meeting with St Dominic and St Francis’ receival of the stigmata. This article will explore the themes of the panel and the innovative way our conservator was able to sensitively bring the full colours back to life.

Above: surface cleaning and varnish removal is usually conducted with small cotton swabs soaked in an appropriate solvent solution 

Saint Francis of Assisi and Saint Dominic

The medium of oil paint began to be frequently used for panel paintings from the 15th century, taking over from previously dominant tempera. The age of this panel makes it an early adopter of oil bound pigments and only 200 years older than the Franciscan and Dominican orders themselves. It is contemporary to the formation of the Third Order of St Francis founded in 1447. The meeting and subsequent friendship of St Francis and St Dominic inspired a tradition for the two orders to meet on each other’s feast day. We can assume that this artwork was likely commissioned in celebration of the order’s mutual support towards a shared goal, perhaps for one of these convivial feast days. 

Above: a detail from The Meeting of Saint Dominic and Saint Francis of Assisi by Fra Angelico, 1427-29

We can further establish the context of this painting from another 15th century depiction by Benozzo Gozzoli entitled Vision of St. Dominic and Meeting of St. Francis. Dated 1452, this artwork captures two important origin stories of the saint’s divine friendship. In St Francis’ vision, God appears to unleash terror upon the world – but is haulted by the Virgin Mary, who placates Him by suggesting two men will work towards the conversion of the world. In this vision, Francis recognised himself as one of these men. The next day a stranger approached and embraced St Francis in church, this was St Dominic. St Francis knew him as the second figure in his vision immediately. St Dominic had shared this vision and told him: “We will work together, supporting one another toward the same end, and no one will prevail against us.” 

Above: depictions of St Dominic including art by Filippo Tarchiani (1607), Carlo Crivelli (1472) and an engraving by Cornelis Cort after Bartholomeus Spranger (1573)

In our client’s panel, the two saints are side by side in a composition that is both united and halved in its narrative. The saints are dressed in the habit of their respective order, St Dominic holds his typical accompaniments of a bible and lily stem, representative of his devotion to the scripture and purity – he also has a star on his robe, a symbol that is commonly found above his head throughout art history. St Dominic looks towards St Francis with a gaze of admiration as he receives the stigmata (the scars of Christ).

Above: a detail of Saint Francis receiving the stigmata – before and after treatment by our conservator

The inclusion of a golden ionic pillar between the two separates the scene, as if to acknowledge that St Dominic was not an actual witness to this miracle – yet still allowing him to view it in an artistic expression of their fraternity. As St Dominic died three years before St Francis, it is also possible that he is looking upon him from heaven. The pillar allows for a landscape to form on the right of the panel, true to the story of St Francis receiving the stigmata from a seraph (a six-winged angel on a cross) on Mount Verna.

Above: depictions of St Francis including art by Cima da Conegliano (1510), Antoniazzo Romano (1480) and Federico Barocci (1600) 

Condition assessment 

Our conservator first assessed the condition of the panel by looking at its structure. There were fears that the base was weakened due to a historic or active woodworm infestation. Woodworm sawdust – also known as ‘frass’ – was evident during this preliminary inspection. Woodworm holes are typical issues to be found on a panel painting of this age and are usually historic in nature, but the evidence of fresh frass requires caution as the pests may have returned. To eliminate any risk, the holes were sensitively hoovered (with conservation suction on a low setting) and the piece was placed in isolation for six weeks to ensure no further evidence was present. This part of the process was conducted out of courtesy by our team, as it provides security for both the artwork and other items in our conservation studio.

Under ultra violet light, the painting had clear areas of overpainting from previous conservation work. Due to helpful labelling on the back of the panel, we were able to establish that a previous restoration was undertaken in 2003. Identifiable by blue fluorescence, we could also see that the painting had a layer of aged synthetic varnish covering the surface.

This synthetic varnish had been applied by the conservator who carried out the previous treatments almost 20 years ago. A plan was put in place that would aim to reveal the true intention of the artist, undercovering the original colours that had become dulled under layers of old varnish and surface dirt.

Above: some areas of overpainting and a scratch to the surface were clearly visible prior to restoration

Removing layers of discolouration

The first varnish layer was readily removable in solvents with a low polarity, these are generally safer for use on oil paintings as they are less likely to swell the binding medium in the paint. However, after removal of the synthetic varnish (that had been applied in its 2003 restoration work), there were still yellow varnish residues visible in the texture of the paint. Our conservator Anna investigated further to see how we might be able to safely remove this.

Above: our conservator tested small areas to remove the build-up of varnish in crevices, this proved to be successful and allowed for a clearer view of the artwork

Appearing as embedded grime, old varnish stuck within the texture of paint is typical in artworks that have undergone several restorations in their lifetime. Each time the painting is cleaned, the most soluble components of old varnish are removed and the deeper varnish within impasto can remain and become built up. Repeated solvent applications are avoided to prevent negative impact on the paint layer, so these difficult crevices are not forced out. Leaving a stubborn, dark and densely packed varnish in the crevices, the issue may be further complicated by dirt being mixed in. Dirt and varnish layers cannot be removed with the same solvents, so the residues become very difficult to remove. This was the case with our client’s panel, as an artwork of its advanced age had likely undergone several interventions during the centuries since its creation.

Above: our conservator Anna picked up these new techniques in our recent MCP workshop as seen above

As the embedded varnish was not safely removable using standard solvent mixtures, the next step was to test a selection of emulsions using recipes from our recent Modular Cleaning Program workshop led by Chris Stavroudis. During this workshop our conservation team had the opportunity to experiment with new cleaning solutions including an emulsion that could be very useful for this type of problem. 

Above: the lighter areas such as St Dominics white robe came up very well following this new technique

Conservation is very much science focused in its approach to cleaning and caring for artworks. The removal of varnish layers and surface contamination comes down to the chemistry of each issue and the modules involved in their chemical makeup. In simple terms, varnish layers are generally soluble in organic solvents (non-aqueous) and dirt layers in inorganic solvents (aqueous). Therefore, using an emulsion with both an aqueous and non-aqueous phase, our conservator could loosen and remove these difficult areas of combined dirt and varnish.

Using the principles of the MCP workshop, the emulsions tested were mixtures of an aqueous phase with a pH buffer, chelator and surfactant, a thickening agent, and a range of non-aqueous solvents. The safest and most effective mixture was determined by adjusting a range of factors including the pH of the solution and percentage of solvent included. The specific emulsion chosen removed the stubborn residues safely, revealing the bright colours of the painting without negatively affecting its composition.

Above: the face of Saint Dominic before and after being conserved with the new emulsion 

The result (seen below in full) allowed the panel to return to its original tones and to a condition that it may not have been witnessed in for hundreds of years. As both a historic oil painting and a piece of religious devotion, it was important that this artwork was stabilised and revived whilst retaining its artistic integrity. Our team was also glad to be able to provide exciting new treatments in the field of conservation to be able to bring it safely back to life. 

How can we help?

If you have an oil painting that requires treatment from our specialist conservators, please get in touch today for further advice.

To make contact please email us via [email protected] or call 0207 112 7576