How to Create a Cyanotype Split Tone in GIMP

This guide explains how to replicate the classic photographic cyanotype split-toning effect using the free image editor GIMP. By converting your image to monochrome and selectively mapping deep Prussian blues into the shadows while introducing subtle warm tones to the highlights, you can achieve a striking vintage fine-art aesthetic. The following step-by-step method uses core GIMP tools such as Desaturate, Colorize, Curves, and blend modes.

Step 1: Prepare the Image and Desaturate

  1. Open your image in GIMP by navigating to File > Open.
  2. Duplicate the base layer to preserve the original photo by going to Layer > Duplicate Layer (or pressing Shift + Ctrl + D). Name this layer "Monochrome".
  3. Convert the layer to black and white by going to Colors > Desaturate > Desaturate.
  4. Choose the Luminance mode for the most natural tonal distribution and click OK.

Step 2: Apply the Cyanotype Blue Shadows

  1. Duplicate your "Monochrome" layer and rename the new layer to "Cyan Base".
  2. Go to Colors > Colorize.
  3. Set the Hue to approximately 0.58 (a rich Prussian/cyan blue).
  4. Set the Saturation between 0.50 and 0.70 depending on the desired color intensity, and adjust the Lightness slightly down if you want deeper shadows. Click OK.

Step 3: Introduce Split-Toning in the Highlights

A traditional cyanotype print often features unexposed paper or chemical toning that shifts the highlights toward soft cream, amber, or pale yellow.

  1. Duplicate the original "Monochrome" layer again and move it to the top of the layer stack. Rename it to "Warm Highlights".
  2. Go to Colors > Colorize.
  3. Set the Hue to a warm amber or pale yellow (around 0.10 to 0.12).
  4. Set the Saturation low, around 0.25 to 0.35, and click OK.
  5. Change the layer Mode (found at the top of the Layers panel) from Normal to Screen or Soft Light.
  6. Lower the layer Opacity to between 30% and 50% so the warm tone gently blends into the highlights without washing out the blue shadows.

Step 4: Fine-Tune Tonal Separation with Curves

  1. Select the top layer and go to Layer > New from Visible to create a merged working layer.
  2. Go to Colors > Curves.
  3. In the Channel dropdown, select Blue:
    • Drag the bottom-left of the curve upward slightly to ensure rich blue remains present in the deepest darks.
    • Pull the top-right of the curve downward slightly to allow the warm tones to emerge in the bright areas.
  4. Switch the Channel dropdown back to Value to adjust the overall contrast into an S-curve for a classic analog photographic look.
  5. Click OK to apply the final effect.