Linda Waters, Conservator Paintings, shares a technique used in her work to look through layers of paint and uncover a painting that would otherwise remain invisible.

Recently we had an opportunity to try to see through paint in the foyer of a building in Taita to find a mural underneath.

Bronwyn Holloway Smith from Massey University College of Creative Arts is undertaking a Mural Recovery Project and contacted Paintings Conservation at Te Papa for assistance. She wanted to see if a mural painted by E Mervyn Taylor in the 1960’s in the foyer of the former Department of Scientific and Industrial Research building in Taita was still under the paint on the walls.

How we use infrared

We have equipment we regularly use to look at the under layers in painting – a camera adapted to work with infrared, and an infrared light source. How it works, or doesn’t, is that:

1. Infrared radiation penetrates the surface of the paint. It is such that you have to adjust the focus of the camera from what you actually see, because IR is deep.
2. Materials react differently to it, either by absorbing, transmitting or reflecting it. Materials that transmit reveal what is underneath them, and those that reflect it can penetrate any transmitting layers over them. Alternatively, reflecting layers can also obscure what is underneath them as the radiation can travel no further.

So, what you actually see is a bit of a lottery, because it depends on the materials and how they have been put together – what sits over what. There is, however, the potential for much information to be gleaned in this way.

A good example of when infrared examination works well is when there is preparatory pencil drawing under the paint and over a priming layer, such as you find in Lindauer’s paintings.

You can see through his paint layers to the sketching that is the foundation for his finely painted portraits. The graphite pencil absorbs infrared, and the lead-white priming paint reflects it, and thus you can see his preparatory work because of the difference between the two.

Different paints and pigments behave in various ways too – we have seen painted under-designs in kowhaiwhai panels for example.

On-site investigation

Out to Taita we went, and set up our equipment. At the time we also had the use of an infrared video camera – old technology, but very useful, as it had a wider range of sensitivity than that of the camera, so was more likely to pick up any paint underneath. The white wall in the foyer – all white, no clues – was our target.

There was nothing to be seen with the naked eye on the surface, no brushstrokes or hints of colour to be seen beneath the top layers of white wall paint to suggest the mural was there.

We worked out where to aim our infrared lights and camera from an old photograph that Bronwyn had, which showed the position of the painting on the wall in relation to doorways and so on.

Alas, despite trying many permutations and combinations of exposure and aperture, we were unable to penetrate the white wall paint. This is because of the combination of the materials, and in particular the nature of the artist’s paint and pigments, as you would understand from the above.

It seems the white wall paint may contain lead white pigment, which reflects infrared, and the artists paint, a modern concoction, perhaps contained synthetic pigments or dyes that are quite transparent to infrared.

Taking a paint sample

What did we do next? Sought physical evidence! We took a small chip of paint from the edge of a screw hole in the wall, within the area the mural should have been, and took it back to the Conservation lab at Te Papa. We mounted it in resin and ground it back to reveal the layers.

And we hit the jackpot – it seems the mural is still there! You can see the coloured layer of paint in the cross section below. It coincides with an area of the same colour on the right of the mural.

Now, the next step is to visit Taita again to take a sample from the other end of the wall in a location that other coloured shapes from the mural are expected to be, to confirm that the mural is there in full. Infrared examination is the always the first port of call – before taking a sample for example – as it is a non-destructive means of analysis with the potential to allow us to see through paint.

Watch this video of our first visit to Taita

An article on the Mural Recovery Project appeared in the Hutt News.

If you would like more detail about infrared imaging see:
Infrared & Ultraviolet Imaging from Smithsonian Museum Conservation Institute
Infrared Reflectology from the University of Delaware