Unique to the chrysotype (gold printing) process are subtle monochromatic hues that range from pink, violet, and purple to blue, grey and black, along with pink/blue split tones. Achieving these colours can be challenging and doing so lies in controlling a number of factors, including the humidity and sizing in paper.
It was an exciting opportunity to illustrate the impact of paper choice and regulated humidity levels on image colour as part of the Convergence Conference in Melbourne, Australia. Hosted by the AIMBI, IPT and the BCA, the conference featured presentations in medical, biological, scientific and creative areas of photographic and visual expertise. A diverse range of educational presentations were delivered that focused on:
- a new microscopic magnification system for focused stacked images of small creatures
- the role of medical/clinical photography in supporting patient treatment
- the simplification of the four colour carbon transfer process
- the application of virtual reality in virology diagnostics and research.
The audience was introduced to chrysotype, a hand-made photographic printing process. In short, an image is created when a solution of gold and iron salts is coated onto 100% cotton paper, dried and/or hydrated, brought into contact with a digital or film negative, exposed to ultra violet light and then taken through a wet bath process. It’s at the drying/hydration stage that regulating moisture levels becomes important to get a desired hue.
Pink and violet hues can be achieved when moisture is reduced (below 40%), darker hues such as blue and black when moisture is increased (above 60%). One straightforward method to reduce moisture is to use a hairdryer with an attached diffuser. With the example below the sensitised papers have been dried in four-minute intervals with a hairdryer to show the effect of reducing moisture.
The longer the print was heat dried, the lower the moisture content and the pinker the shadow areas became. Some precautions when drying with this method – don’t hold the hairdryer too close to the paper and ensure an even flow of warm air (keep it on low). Doing these will help avoid hot spots forming on the paper that can cause uneven image formation.
 The Australian Institute of Medical and Biological Illustration (AIMBI), The Institute of Photographic Technology (IPT) and the Bio Communications Association.