Why Paintings Fail: Cracking, Yellowing, Blooming and Flaking

DRYING CRACKS are wide, open, irregular, and appear within months to a few years. They are caused by a layer drying and shrinking over one that was still moving — the fat-over-lean violation, or a drier-loaded upper layer. AGE CRACKS are fine, follow a regular net, and take decades. They come from the support moving with humidity and temperature while the paint film has slowly become less flexible. They are largely inevitable and largely harmless. So the width and the age of a crack together tell you which you have. Wide cracks in a young painting are a recipe fault; a fine net in an old one is the material behaving as materials do.

Linseed oil yellows as it ages, and it yellows MORE in the dark. A painting kept in a cupboard for a decade comes out noticeably warmer, and much of that reverses after some weeks in daylight — which is a genuinely useful fact. Varnish yellowing is separate and does not reverse. An old dammar layer can be distinctly brown, and removing it can transform a painting — which is what cleaning does, and why the results are sometimes controversial. Choosing a less yellowing oil helps: walnut and poppy oil yellow less than linseed, at the cost of drying slower and forming a weaker film. Using them for whites and blues only is a traditional compromise that follows directly from that trade.

FLAKING is adhesion failure between layers — the ground and the support, or two paint layers. It means two materials that did not bond or that move at very different rates, and acrylic over oil is the textbook case. CUPPING is paint islands curling up at their edges between cracks, which happens when a strong film sits on a support that has shrunk. It is a support problem presenting as a paint problem. BLOOM is a milky haze in the varnish from moisture trapped during application. It is the only common fault that is often fixable: gentle warmth, or re-forming the varnish with a little solvent vapour, frequently clears it — which is worth knowing before anyone reaches for anything more drastic.

The whole batch reduces to four decisions, all made before any paint is applied. A rigid support or a flexible one, matched to a ground that suits it. Lightfast pigments. Each layer fatter and slower than the one below. A varnish applied late and removable. None of those cost money or time at the moment of deciding, and all of them are nearly impossible to correct afterwards. That is the same shape as wood movement, glaze fit and print orientation — the decisions that matter are early and cheap, and the failures are late and expensive. So write it on the back. What it is painted on, what with, and when — so that the next person to look at it closely, whether that is a conservator or you in thirty years, is reading a record rather than guessing from the damage.