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Lighting Techniques

Raking Light

Simply placing a light at an oblique angle to a painting can reveal information clearly. Raking light is often used to document craqeulure, cupping or tenting paint, uneven tension in a canvas, or warp in a painting on a panel support. We are researching the use of more accurate surface mapping techniqes to complement this techhnique

In the image above, the indentations around the 3 punctures to the painting are evident. It also shows the canvas texture, indicating that the paint was applied in a thin and fluid state.

Specular Light

Recording how light is reflected from the surface of an object can help to provide information about the structure beneath. This technique, when used with a degree of enhancing with digital imaging, can illustrate quite subtle variations in the surface. In many instances, when used with wooden surfaces, the original tool marks can be clearly seen. In other instances virtually invisible indentations can be identified, which may provide vital information to the conservators.

Detail of an area of the Westminster Retable. The toolmarks left in the wood are rendered clearly visible in specular lighting

Transmitted Light

In some instances transmitted light can be used to provide information not otherwise visible. Light can be used to pass through the picture to image layers below the surface and the structure of the substrate. Although the outer layers may mask some of the information, useful data can still be gained about the history or make up of the object.

The transmitted light image above is taken from a detail of a vellum page in a medieval manuscript. The page has been used twice, with the original design being covered over at a later date. Transmitted light image lets us see part of the obscured pattern image beneath.

Dark Ground or Dark Field

Although dark ground illumination is commonly used in microscopy, we have adapted the technique to use on a larger scale. In this way very fine detail can be recorded that would otherwise be virtually invisible to the naked eye. This is again a useful source of research material and photographic documentation.

Photographic Services - Lighting Techniques - Dark Ground

The faint powdery deposits on the reverse of the glazing, seen in the image above, make the sitter clearly visible even though the painting has been removed from the frame.

The deposits on the glass, clearly visible in the image above were only faintly visible under normal lighting. They were analysed and found to be a combination of mineral and fungal deposits, drawn differentially to the glass because of the differing paint surface below.

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Conservation Blog now available

Jun 22, 2017

Conservators at the Fitzwilliam Museum have started a blog.

A Brush with Royalty

May 24, 2017

The Hamilton Kerr Institute has just completed the restoration of two portraits attributed to Nicholas Hilliard

HKI wins 2017 Museum and Heritage Award

May 18, 2017

Conservators at the Hamilton Kerr Institute have won the 2017 Museums and Heritage Award for Restoration/Conservation for their Restoration of Sebastiano's Adoration of the Shepherds.

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