How Old Paintings Age: Varnish, Lead Soaps and Fading Blues
An old painting is an image carried by materials with different histories. Changes in a coating, a pigment or a supporting canvas call for different explanations, even when they all affect the surface seen by the viewer.
Looking at condition begins with a simple question: which part of the object is changing? The examples below separate varnish, paint and support. That separation makes it easier to understand a conservation account without treating every alteration in appearance as the same process, or assuming that one treatment addresses every kind of change.
Yellowed varnish and its removal
The Rijksmuseum's Operation Night Watch account describes the removal of old varnish after five years of intensive research. The work takes place with microscopic precision in a specially designed glass chamber, before the public. The sequence of research followed by treatment is central to the account: the visible operation is part of an investigation of a particular painting, rather than a general recipe for cleaning pictures.
At the National Gallery, the 14-month restoration of Rubens's The Judgement of Paris involved removing and replacing discoloured varnish and retouchings. The Gallery describes difficult decisions about whether to return to Rubens's composition or retain later changes. Treatment followed the level of a previous cleaning in the 1940s, and retouching sought a more coherent balance using more stable materials.
That example makes a useful distinction between removing a discoloured coating and choosing which historical state to present. The Gallery's cross-sections showed later modifications above a varnish layer, separating them from Rubens's own revisions. Material examination clarified the sequence; it did not make the decision about later alterations disappear. A treatment account is easier to follow when evidence about layers and decisions about presentation are read separately.
Lead soaps breaking the surface
A 2026 paper on lead soap protrusions, involving the University of Amsterdam and Rijksmuseum, examines a recognised form of degradation on historic oil paintings. The paper stresses that the processes causing lead soaps to gather in particular places and break through paint layers remain poorly understood. It proposes four scenarios for nucleation, considering reactive lead minerals, phase separation and reverse micelles.
These are proposed mechanisms, not a single settled explanation for every protrusion. The paper allows that more than one scenario may apply to historic paintings, with differences related to paint composition and environmental conditions. For a reader, that uncertainty is part of the finding. Identifying a phenomenon and explaining exactly how it developed are different achievements. It is possible to recognise a material problem while continuing to investigate the processes behind it, and a description of visible damage should not be mistaken for a complete account of its cause.
Colours that change
The National Gallery's Rubens investigation identified smalt in the sky and more costly ultramarine in Venus' cloak. Its account describes smalt as a blue that fades towards grey over time. The two findings concern both the painter's choice of materials and the changing appearance of the picture. A grey passage cannot simply be discussed as though its present colour necessarily records an unchanged choice made at the easel.
The useful question is specific: what evidence connects this colour to this material in this painting? A pigment identification and a statement about its behaviour provide a firmer basis than a broad assumption that all old blues have changed alike. The Rubens example offers a documented case; it is not a rule for every sky or cloak.
The canvas beneath
A 2025 study of the lining canvas of The Night Watch reports that the original canvas has deteriorated significantly. The lining is now the main load-bearing component. The study examined mechanical properties at the levels of fibre, thread and canvas, distinguishing the fibre material itself from the combined behaviour of fibres, wax resin and voids.
The analysis related properties at those different scales, allowing predictions about canvas behaviour from fibre-level measurements. This shifts attention from what is painted to what carries the paint. The lining may be less prominent in a viewer's encounter with the image, yet the study shows its structural importance in this particular object. Surface appearance alone is therefore only one part of the condition described by the research.
Permanence as a discipline
These examples suggest a way to read accounts of ageing: identify the component, the observed change, the evidence and the remaining uncertainty. Varnish removal, an explanation for protrusions and a study of canvas mechanics address different questions. Keeping them distinct gives the word conservation a more concrete meaning. The aim of understanding an old painting is served by attention to the whole object, from the visible image to the material structure that continues to carry it.