Before buying a work of art, four fundamental questions must be answered: authenticity, condition, fairness of price and the seller's title. Due diligence is the process of analysis that answers these questions. For attribution and authenticity in particular, it relies on three interdependent pillars.
1. Connoisseurship (stylistic and expert examination)
This is the visual analysis carried out by a specialist in the artist, who assesses the handling, the typical materials, the compositional choices, the habits of signature and the recurring anomalies. Although it is the oldest tool and, as a rule, the first to be used, it is a critical judgement that depends on who formulates it (specialist training, documented experience of the artist, recognised publications, independence from the market) and on the possibility of comparison with works of certain authorship. An opinion that does not set out its evidence, however illustrious the signature, is not an element of due diligence. Attributions may change over time as historical research progresses.
2. Historical and documentary reconstruction (provenance)
This concerns the traceability of the chain of ownership from the work's origin to the present day, including passages through galleries or auctions, exhibition history, citations in catalogues raisonnés, and labels and stamps on the reverse. A documented and verifiable provenance is a strong indicator, but it is rarely sufficient on its own: documentation can be forged and cannot be the only proof. A complete chain is the exception: gaps are frequent and must be declared, not concealed, and a name close to the artist is reassuring only if documented.
3. Scientific and technical analysis
This draws on scientific analyses (X-radiography, reflectography, ultraviolet fluorescence, and chemical analysis of pigments, binders and supports), entrusted to qualified, independent laboratories, with a report that describes methods and results and distinguishes data from interpretation. A fundamental principle applies here: science rules out, it does not prove. The presence of a material that came onto the market after the artist's death, unless attributable to a restoration, rules out that the work is by the artist's hand; conversely, the compatibility of the materials with the period proves only that the work could be authentic, but does not establish its authorship.
Combining the evidence and handling uncertainty
The three tools balance and correct one another: the expert eye can be deceived by a refined forgery, a provenance can be fabricated and scientific analyses can be circumvented with period materials. Applying them together reduces the margin of error and makes it possible to set out the elements of uncertainty transparently; these must never be concealed. A positive opinion as a rule requires the convergence of all three tools; a single contrary element, once established, may be enough to rule out the attribution. When the results diverge, the work must be presented as uncertain and the buyer decides in full awareness of the risk.
The role of the coordinator
The art advisor or appraiser who manages the due diligence does not issue an authentication, but coordinates the whole process: gathering the opinions of the qualified scholars of the artist and, if living, of the artist and, where they exist, of the archive or the foundation, opinions whose qualifications and evidence are verified, and commissioning analyses from independent laboratories. Their task is to assess the overall strength of the three checks and present the client with a clear picture of what is certain and what is in doubt; on that basis the appraiser accepts or rejects a presumption of authenticity.