Mapping the surface with 3D scanning
A new way of condition reporting
3D scanning is a relatively new tool for documenting artworks and their technique and condition. There are different projects and tests underway internationally with interesting perspectives for the future use of it in conservation and technical art history.
At SMK we decided to test it as a possible tool for precision condition reporting. In collaboration with the company MOEF we wanted to see just how well we could reproduce a structured surface such as that of a painting. How small changes can be monitored this way? That requires very precise high resolution scans.
We decided to test the technique on two Tal R paintings in the collection. Tal R (1967-) is among our very best painters and Made in Heaven and Name, Rank and Departure from 2005 are central to his production – and consequently to SMK's collection.
Tal R works in series and every time he begins a new series of paintings he establishes a set of dogmatic rules or stumbling blocks with relation to the materials, painting style, or motif. In this series he has limited his palette to just seven colours, yet the paintings are pastose with large amounts of oil paint, which has been squeezed directly out of the tube and onto the canvas in several areas. The paintings are painted on a gesso ground and mounted on wooden boards.
Museums and galleries make condition reports of their works of art when borrowing from each other. The purpose of the report is to agree on the physical condition of the – oftentimes very valuable – works. This serves to clarify where an incident has occurred in case of damage during transport and/or loan.
The condition reports are drawn up by conservators and usually consist of a tick-box system with different standard values, aided by photographs where different observations can be marked. The inspection itself is primarily visual and aided for example by a hand-held torch, magnifying glasses, or UV light. The idea of 3D scans is to have an even more precise way of documenting certain areas if needed.
The technique we employed is called structured light scanning or white light scanning. Roughly speaking the scanner is built of a projector and two cameras. A number of thin lines are projected onto the surface and recorded by the cameras. By means of the position of the cameras the computer calculates the position of each of the 1,4 million pixels. When connected to a surface this cloud of coordinates gives a single scanning. To make sure all parts of the surface structure are documented every area is scanned from several angles (each scan has a different colour on the screen). When overlaid these scans create an accurate digital 3D copy of the painting's surface without touching the painting or physically attaching measuring points. The level of detail is dependent on the type of scanner. This particular equipment is mobile, which is an advantage with heavy or large works of art such as the Tal R paintings.
Use and Perspectives
3D scans provide a highly detailed rendition of the paintings' surface with or without the actual colours. To leave the colours out can make it easier to see and 'read' any phenomena in the structured surface. The scan can be used for digitally measuring details or to compare differences over time when overlaid with a second scan from a later date. For instance, if there is a paint loss or other changes to the surface, this will be highlighted by a colour coding system. The darker the colour, the bigger the difference between the two scans.
In case of loss the documented topography of the original surface can be used as a reference for any future restoration efforts. There have even been experiments with printing 3D copies of paintings based on scans like these – but SMK has no such plans!