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Saint Barbara Sculpture from a 15th Century German Wood Altarpiece

Over many centuries, this sculpture had collected several old repairs and restorations.  It was accessioned by a museum despite its inconsistent restorations, and when the museum was able to prioritize its treatment, the old repairs were assessed, and many of them were removed and improved. 


Wood is an organic material, and as such, it can be unstable.  When plant or animal tissue is removed from the organism which generated it, a process of physical and chemical change immediately begins.  Light exposure, changing 

Carved wood Saint Barbara sculpture

humidity levels, pollution, pests, and handling can all accelerate the decay process, so aging wood is rarely in pristine condition.   


For its age, this sculpture was in excellent structural condition, with no cracks or breaks in the carved, solid body, and no evidence of pest damage.  But the original gesso and polychrome had degraded, then been filled and thickly overpainted, disfiguring the figure’s face and parts of her chest and hands, as well as her crown and hair. 

Detail of thick tempera paint on old fills

Detail of overpainted fills and cracked gesso

Cleaning in process.  A vertical line can be seen at the middle of the neck and face, where the cleaning on the right side of the photo has stopped.  The chest has not yet been cleaned.

The first step was to gently clean the surface.  Layers of beeswax had been added over many years, and had presented a sticky surface to which smoke and dust were attracted and clung.  As the beeswax and grime were removed, the extent of the old restorations came into focus.


A conservative touch was used when cleaning.  Over-cleaning the complex patina from an older object can cause the surface to looked stripped or “skinned,” and can also begin to remove the older layers of polychrome.  An important ethic of good conservation is to preserve all original material, so the cleaning was thorough but not invasive, and left behind enough patina that the figure looks clean but not scrubbed of all aging. 

Detail of face, with tempera paint cleaned off and fills exposed

Detail of exposed fills and abraded left cheek

Next, the tempera paint was removed.  Cleaning back old restorations relies on identifying and preparing solvent gels that solubilize newer paint layers without removing the original underlying pigments.  As the newer tempera-based paint layer was removed from the surface, it became apparent that a series of underlying fill layers were also cracked and damaged.  The fills had changed shape, expanding and contracting so they were no longer level with the surface.  Some of the original paint under the wax and facial restorations had also been deeply scratched, suggesting that an aggressive old cleaning treatment (perhaps involving sanding) had gone wrong.  

In cases where there are several layers of restorations, each layer of restoration has to be considered separately, both for its material qualities and for its historic importance.  At some time during the 17th or 18th century, the undamaged original red paint on this sculpture was over-painted with a brighter red pigment. The remnants of the overlying pigment were stable, and strongly bonded to the original paint, and removing the layer would have been risky to the original underlying surface.  The newer paint also 

Detail of the robe, showing both layers of red paint.  The pencil marks were removed, but the newer layer of red paint was left intact.

hinted at a time when bright colors may have been prized by people more than original surfaces.  After close curatorial consultation, it was decided to leave both layers of red intact.  


The next step was to reduce the old fills.  The material was impossible to fully remove without risking damage to the surrounding original material, so it was only partially removed, then a water-soluble resin was used to fill and shape the tops of the missing areas.  Another important ethic of art conservation involves ensuring that treatments and additions are as reversible and “retreatable” as possible.  Materials are always chosen with future reversibility in mind.  With that goal in mind, the conservation treatment was completed by touching in the new fills with easily-reversible conservation grade acrylic emusions.

These procedures were all repeated on sections of the sculptures' crown, hair, hands, and feet, as well as on  the symbolic tower and book the figure holds in her hands.  

Preparing to touch in color to fills, using archival pigments reversible with mineral spirits

Detail of left cheek with new fills smoothed and ready for color

Detail of left cheek after treatment is complete

Detail after treatment

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