National Trust Painting Conservation Adviser, Christine Sitwell, describes some of the scientific techniques behind one of our biggest and most challenging conservation projects.
In 1840, Guido Reni's fresco 'The Separation of Night and Day' was removed from its place of creation, the plaster ceiling of Palazzo Zani in Bologna.
The fresco was in a poor state, a deciding factor in the palazzo's owner, Count Pallavinci, having it removed to make way for a new decorative scheme.
For the 19th-century removal men, came the delicate task of physically removing the thin, painted plaster layer of the fresco and attaching it to a canvas support. Not an easy job considering the painting was already damaged and, according to contemporary accounts, covered by wire mesh to stop it falling down.
As it turned out, the careful operation proved too fragile and left the fresco yet more damaged and missing areas of paint. In the 19th-century, the conservators' solution to such damage was simply to over paint large areas, covering the bald patches on a canvas but also much of the surrounding intact paint.
A key part of our conservation of 'The Separation of Night and Day' has been to remove this over paint, and discoloured retouching from 1960, to reveal the original paint underneath.
Stripping away the layers to reveal a true fresco
Our first challenge was choosing a solvent that would strip away the 19th-century varnish and paint without indiscriminately removing the precious fresco work below.
So before the conservation treatment began, cleaning tests were undertaken to determine which solvents could be used to safely remove the later additions without taking the original paint with them.
Conservators Bush & Berry then spent about 2 months gently rubbing solvent-dipped balls of cotton wool over the surface of the over paint to dissolve it away.
Analysis of paint samples from the fresco also provided valuable information about the painting technique and the condition of the original fresco.
We discovered that it was a true fresco: the application of pigments suspended in water applied to damp plaster. The technique was most famously used by Michelangelo in the Sistine Chapel, Rome.
The removal of the darkened varnish and the large areas of over paint revealed the true quality of the fresco.
© National Trust / Stephen Young
Sadly, many of the old losses were clearly visible. Careful retouching using a water based medium called casein (basically soured milk) has now once again restored the fresco to its original, wonderfully light appearance. Casein was chosen for its matt qualities, which matched the original painting, and the ease by which it can be removed, if needed, in the future.
The whole conservation treatment took around 8 months.
Setting the scene
We also wanted to recreate the appearance of the Library at Kingston Lacy as it was in a 1904 Country Life photograph, the earliest photograph that showed the painting in the house.
The black and white image shows a two-toned ceiling, dark walls and a heavy frame with side frames around the painting:
© Country Life Picture Library
We were helped by the Kingston Lacy archive. A note from Daphne Bankes recorded that her father, Walter Ralph Bankes (1853-1904), chose a red colour for the walls because he liked the deep red shade of the baggy trousers worn by the Zouaves of the French army.
We needed to find this colour. Paint samples were taken from the walls and they revealed a dark red layer which had subsequently been painted over by two more red layers.
By carefully removing the top layers to expose this red layer and using a spectrophotometer (an instrument for measuring the colour of a painted surface) we were able to measure the colour and have paint made which matched it.
Unfortunately, paint samples from the ceiling failed to provide information about the colours of 1904. The colours had been removed when the ceiling was papered over and repainted after our acquisition of Kingston Lacy.
At this stage luck stepped in. The painting had been restored in 1960 and we managed to trace the conservator’s widow.
She provided a slide which showed a painted sky and pale ochre borders around the frame. Even though it wasn't the scheme on the 1904 ceiling it shaped our final decision to use a light blue colour as the background with the bands around the frame painted a light ochre.
After 23 years, the painting is back on the Library ceiling at Kingston Lacy, surrounded by the newly recreated frame and set within the recreation of the 1904 Library scheme.
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