XRF Analysis and Micro Fading
During the description and condition reporting phase for The Key, it was analysed using our portable XRF probe. XRF is X Ray Fluorescence. It is a non-destructive test and works by firing X-rays of a known energy level at a sample, which then reflects X-rays of a different energy level back to the probe. Every chemical element reflects X-rays of a unique energy signature, so the probe can tell you what elements you have in your sample by what X-rays it is receiving back. The way it works is that X-rays from the probe knock an electron out of the lower rings of atoms in the chemical elements of the sample; another electron from a higher ring then drops down to fill the gap, and the energy released by the electron dropping down is received and recorded by the XRF probe.
The analysis of The Key gave us a strong iron (Fe) reading, which confirmed our assumption that it is a ferrogallic print.
With the Centenary of Canberra coming up in 2013, and the desire for the Archives to exhibit the Federal Capital Design Drawings, it is vital that we develop a better understanding of how stable all the entries are in light. Red inks are known to be vulnerable to fading, as are dye-based stamp pad inks. Paper supports will darkened with age, and we wanted to see if this would be further affected by light exposure too. The opportunity was taken during this testing to establish the stability (or otherwise) of Item 51.
The technique we used for measuring the colour change of the dyes and pigments on exposure to light is Micro Fading. In the micro fading process a tiny beam of very strong light is directed at a material and its fading behaviour is recorded. The spot tested is microscopic and the fading is only allowed to progress as far as one ‘just noticeable fade’ – the minimal colour change discernible by the human eye.
The areas tested on our print were the paper itself (to measure darkening rather than fading), the ferrogallic image, the red ink, the black ink and the graphite pencil.
The graphite pencil and the black ink were shown to be stable. The image lines and the paper did change colour, but not dramatically, but it was the red ink that produced the most significant result. The red ink falls into the category of having a “high responsivity to light”.
Once the result for the red ink was in, the stamp pad inks were not tested as it was apparent already that the red ink would be the limiting factor for any display.
The reactive nature of the red ink to light means that if the print were to be displayed, it could only be for a limited amount of time (no more than six months) and during that time the light levels would have to be low (no higher than 75 lux with no UV content).