The traditional Sabatier effect

The Sabatier effect which is also referred to as soloarisation , is a traditional process of exposing a print to white light for a secong time during its development. This in turn reverses the tonal curve on certain parts of the image. The result; an image that is part positive and part negative. 
It was somewhat perfected by Armand Sabatier but the the phenomenon was first documented by a H. de la Blanchere in 1859 in L’Art du Photographe. Having said this, solarisation was already known by Daguerre and is known to be one of the earliest effects in photography.

Throughout the years, this technique has been perfected by a number of well known traditional photographers such as Hershel and more recently by Man Rays assistant Lee Miller where she accidentally discovered this technique. There are many who claim to have 'discovered' this technique throughout the years.

Solarised Portrait of Meret Oppenheim, Paris, 1930

Solarisation is most effective when it is used on a photograph that has a high contrast, lines can appear between the light and dark areas which is a phenomenon known as a Mackie Line. A very interesting blog post debating the origin of the Mackie Line can be found here

I have witnessed several methods/processes to master this technique but I think a lot of it is trial and error.
I will be heading into the darkroom next week to trial the below method.

1. Print a test strip with the enlarger set to f11, 170M and expose the strip 4 seconds at a time
2. Develop the test strip as normal.
3. Expose a whole piece of 10×8 paper for the time that worked best for the image and half develop the image until it is light grey.
4. Place half developed print in water quickly.
5. Remove excess water with a squeegee and place in the dryer (in darkroom).
6. Once the image is dry, re-expose the image on an empty enlarger with the settings f5.6 and 1/2 at 2 second intervals.
7. Develop this print as normal and evaluate outside – this is the solarised test strip.
8. Repeat the above process using the exposure times that have worked best.

I will add my experience and images next week also....