Reading a Painting’s Condition: Craquelure, Overpaint & UV

Ask a dealer what makes two paintings by the same artist, of the same subject, the same year and the same size differ in price by four times, and the answer is usually not scholarship. It’s condition. A picture can be entirely genuine and still be half modern paint, flattened by an old restoration, and scrubbed of its glazes. Condition is the part of a painting’s value you can actually inspect yourself — and the part that catalogue photography is best at hiding.

UVThe cheapest tool that exposes restoration

%Losses are measured as a share of the surface

1Face matters more than a whole background

The damage vocabulary, illustrated

Tap a term. Each one shows what the surface looks like, whether it is stable or active, and what it does to value.

Craquelure

Normal for age

The network of fine cracks that forms as oil paint and its support age at different rates. On a genuinely old picture it should be there — an eighteenth-century panel with a perfectly smooth surface is a question, not a comfort. What matters is whether the cracks are stable and closed, or open with lifting edges.

Value: neutral. Expected, and part of what tells you the picture is old.

Extreme close-up of the eyes in the Mona Lisa showing a dense network of fine age cracks — Craquelure on the most famous painting in the world. Cracks are not damage in themselves — they are the surface telling you its age. Detail of Leonardo’s *Mona Lisa*, public domain, via Wikimedia Commons.

Four lights, four different pictures

Conservators don’t guess; they change the light. Each one answers a specific question, and the first two cost almost nothing.

Raking light A lamp almost parallel to the surface. Reveals texture: cupping, planar distortion, dents, canvas weave, and the ridges around filled losses. You can do this with a phone torch.

Ultraviolet Old varnish fluoresces a milky green; newer retouching stays dark and flat. This is how you see, in seconds, how much of a surface is not original.

Infrared Sees through upper paint layers to underdrawing and changes of mind. Used for attribution as much as condition — copies rarely have working underdrawings.

X-radiography Shows structure: tears, patches, nail holes, stretcher shadows, and whole earlier compositions hiding beneath the visible one.

A painted figure photographed under ultraviolet light, with dark patches revealing extensive later retouching — The same detail under UV. The dark, flat passages across the face and shoulder are later paint — invisible in daylight, unmistakable here. Photo by Minnesota Historical Society, CC BY-SA 2.0, via Wikimedia Commons.

Ask for the UV images. A seller who has them and won’t send them has told you what they show, and a seller who has never taken them is selling a picture they haven’t examined.

Score a picture before you bid

Tick what the condition report, the photographs, or your own torch tells you. The weighting reflects how the market actually discounts each problem.

Stable, closed craquelure consistent with the age Retouching over more than about 20% of the surface Overpaint on the focal point — a face, hands, a signature Active flaking, cupping or tenting anywhere A repaired tear, puncture or patch Relined or transferred to a new support Surface “skinned” — thin, abraded, glazes lost to harsh cleaning Discoloured varnish, otherwise sound Trimmed, cut down, or enlarged from its original size

Condition risk Nothing flagged

Tick what applies. Note that the first and last items are common and cheap to live with — the expensive words are “overpaint” and “skinned”.

A guide to the questions, not a valuation. Weightings reflect general market behaviour; a rare picture by a major name forgives far more than a decorative one by a minor hand.

What restoration does to price

Honest, minimal, reversible work is fine. Filled losses in a background, retouching that stays within the loss, a fresh varnish — these are maintenance, and no old painting is without them.
Overpaint is different from retouching. Retouching fills a hole; overpaint covers original paint that was still there. It is the single most damaging thing a previous owner can have paid for.
“Skinned” is close to fatal. Aggressive cleaning removes the thin final glazes that carried the modelling and depth. Nothing brings them back, and the picture will always look flat next to a good example.
Relining is a discount, not a disaster. It stabilised thousands of paintings, but old hot-iron methods crushed impasto. Many collectors will pay a premium for an unlined canvas for exactly this reason.
Location beats quantity. Two percent of loss across a sitter’s face costs more than twenty percent in a dark corner.
Works on paper have their own list: foxing, mat burn, light staining, tape residue, and trimming inside the platemark — that last one can halve the value of a print.

Getting a real condition report

Request it in writing before bidding. Auction houses provide them on request, and the report — not the catalogue photograph — is what describes the object.
Ask specifically for UV images and a raking-light shot. Also ask whether the picture has been lined and when it was last restored.
Read for omissions. “Appears to be in good overall condition” with no mention of retouching means nobody looked with a lamp.
Get your own opinion on anything expensive. An independent conservator’s inspection costs a small fraction of the hammer price and will tell you, in an hour, what a decade of ownership would.
Never test or clean it yourself. Solvents, bread, onions, and every other internet remedy remove original paint. See how to care for an oil painting safely.

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Working out what you’re looking at first? Art Scan: Painting Identifier suggests the likely artist, period and style from a photograph, and Art Identifier Museum Guide fills in the context. Condition, though, is a physical examination: torch, UV lamp, and ideally a conservator standing in front of the actual object.

Expected with age: Craquelure, some retouching, an old varnish
Urgent: Cupping, tenting, active flaking — it is losing paint now
Worst for value: Overpaint on the focal point, and a skinned surface
Cheap fix: Varnish removal and replacement, by a professional
Free tools: A phone torch at a raking angle, and a UV lamp
Always request: The condition report plus UV images

The takeaway

Learn six words — craquelure, cupping, loss, overpaint, lining, skinned — and you can read most of what a painting has been through. Shine a torch across the surface, ask for the UV photographs, and price the picture in front of you rather than the one in the catalogue. The best buys in any sale are usually honest, untouched pictures under dirty varnish; the traps are the ones that look suspiciously fresh for their age.