Examining Preliminary Sketches and Compositional Changes using Infrared Reflectography

  • Posted by: Kristin de Ghetaldi
  • Posted Date: August 12, 2014
  • Filed Under: Conservation


Pietro da Cortona and other artists of the seventeenth century would often sketch objects, landscapes, and figures during the initial stages of oil painting.  Most preliminary sketches (whether they are done using a wet medium like oil paint or a dry medium like charcoal) are not evident to the naked eye as they are often covered by several paint layers.  Through the use of infrared reflectography (IRR) the conservation team was able to reveal portions of the preliminary sketch and compositional changes in Pietro da Cortona’s Triumph of David.

The IRR analysis was a collaborative effort between Washington and Lee University and Villanova University.  In order to examine this large-scale painting, a series of IRR images were collected using an Indium Gallium Arsenide (InGaAs) instrument which is sensitive within the 900-1700 nm range (near infrared).  When exposing the paint surface to infrared light, certain pigments appear partially or completely transparent. Carbon blacks will still appear dark in IRR because these pigments readily absorb infrared light.

The depth to which infrared light penetrates depends on the type of paint, the thickness of the paint layers, and the wavelength of infrared exposure.  In some cases, underdrawings or preliminary sketches may not be visible using IRR, as is the case when an underdrawing has been done using white/red chalk or paint that is not rich in carbon black.  For this reason, additional imaging techniques – such as multi/hyperspectral imaging and X-radiography – can contribute to the analysis of a painting’s underdrawing.

Once the IRR images are collected, they must be imported into image processing software and manually stitched together.  The product of these stitched images is referred to as an infrared reflectogram mosaic.  Below are images showing the mosaicing process for the Triumph of David.  When completed, this mosaic will be a compilation of 220 IRR images



King Saul’s crown was initially placed much higher and the contours of his mouth, beard, and face have been altered (originally, Saul was depicted in profile).


Abner’s helmet was originally placed much lower and was embellished with a very large feather plume.

David’s hand had been placed higher on the sword (above where the guard presently resides).  The sword guard and pommel are especially prominent as they contain a significant amount of carbon black pigment.



Keara Teeter

conservation intern




van Asperen de Boer, Jan R.J. “Reflectography of Paintings using an Infrared Vidicon Television System.” Studies in Conservation 14 (1969): 96-118.

Bomford, David, ed.  Art in the Making: Underdrawing in Renaissance Painting, National Gallery London Publications; Yale University Press, 2002.

MacBeth, Rhona. “The Technical Examination and Documentation of Easel Paintings.” In The Conservation of Easel Paintings, edited by Rebecca Rushfield and Joyce Hill Stoner, 296-300. Routledge: London and New York, 2012.

Recent Developments in the Technical Examination of Early Netherlandish Painting: Methodology, Limitations and Perspectives (M. Faries and R. Spronk, eds), Brepols Publishers.

Real, William A.  “Exploring New Applications for Infrared Reflectography.”  The Bulletin of the Cleveland Museum of Art 72 (1985): 390, 392-412.

Saunders, David, Rachel Billinge, John Cupitt, Nick Atkinson, and Haida Liang.  “A New Camera for High-Resolution Infrared Imaging of Works of Art.”  Studies in Conservation 51 (2006): 277-290.

Taft, W. Stanley Jr., and James Mayer. The Science of Paintings. Springer: New York, 2001.


  1. Comment by Rachel — September 4, 2014 @ 9:37 am

    I never imagined Cortona would have changed Abner’s helmet so drastically. It looks to be a different style entirely.

  2. Comment by いい線 — June 3, 2015 @ 12:04 am

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Last Modified: August 12, 2014