The effect is achieved by exposing the print to light partway through the development process. The effect produces halo-like lines (Mackie Lines) between adjacent highlight and shadow areas producing an effect commonly known as solarization, though it is more accurately called the Sabattier Effect. The effect can be done with prints or negatives and can be varied in many different ways to give the positive/negative effect.

1) Start with a negative of normal to high contrast and high contrast paper/filter.

2) Make a standard test strip using slightly larger than normal increments (5 seconds).

3) Develop for standard time in developer.

4) Rinse off as much developer as possible. Don't use Stop Bath. Squeegee off any excess water and be careful with emulsion as it is soft. Use a tray to keep chemical from getting on enlarger station.

5) Remove negative from enlarger. Stop down the aperture about 2-3 stops. Make another test strip but at right angles to the last test strip.

6) Develop normally, including stop bath, fixer and wash.

7) Choose desired times.

Notes:

You can vary many things including:
Setting the enlarger slightly out of focus will broaden the Mackie lines.
Using a less contrasty negative will have broader Mackie lines also.
Removing first print quickly in development process.
Using a second more diluted developer shifts color.
Using a warm tone developer and a cold tone devoloper will shift color.
Age the print anywhere from 15 minutes to a week.
Dodge or Burn to tweak an image.
Bleach the print later to lighten the Mackie lines.

Image by Pedro Costa