Direct Blue Toning

Direct Blue Toning gives to the prints a very, very brilliant blue appearance. The color comes from the deposition of the compound prussian blue, or ferric ferricyanide, on the print.

In this post I will discuss:

1. The formula and procedure for direct blue toning

2. Sample images

3. additional practical toning details 

1. Formula for  direct blue toning (makes 1 L)

500 mL warm water
Ferric ammonium citrate 8 g
Potassium ferricyanide 8 g
Acetic acid 28% 265 mL
Water to 1 L

Toning is achieved by immersing the image in the toner for the desired amount of time. Usually about 2 minutes for complete toning. The toning action weakens considerably after the first few prints, so toning times should be extended accordingly. The following set of images from top to bottom show three toned image (toning carried out for 2 minutes, 30 seconds, and 20 seconds) and then an untoned image for reference.

The images can be untoned by washing in basic water (for example water with some potassium hydroxyde or print developer). You can see a small example in the right edge of the second print above.

The final image is composed by 

1. deep blue ferric ferricyanide (prussian blue)

2. white silver ferricyanide

3. some residual silver, the amount of which depends on the length of the toning procedure.

The longer the toning time, the more the print is intensified (i.e. the darker areas become darker). This is because the prussian blue is a much larger molecule then the original silver.

2. Sample Images

Bright sunny scenes with an open sky look exceptionally when blue toned. Note how the blue toning intensified the print, which in this case perhaps turned too dark when toned. Account for this by printing lighter.

Less "open" forest scene do not look as good when blue toned. In this case I prefer the hue of the sepia/selenium toned version to the right.

Snow scenes look great when partially blue toned. In this example you can see how, in a partial toning, the darker parts of the image are toned first (the darker part of the sky has more blue than the lighter central part of the image).

 Scenes containing metallic objects look amazing in a partial blue toning.

Scenes containing water look OK when blue toned. The bright blue color is not exactly a perfect match for the color of the sea, so your mileage may vary.

3. Additional details

Washing the print can alter its color:

- extended washing can move the color to more of a slate/navy blue

- washing with slightly basic solution (1 g/L sodium carbonate is a good starting point) will slowly convert the color back to grey

- washing in acid water (a few drop of HCl, acetic acid, citric acid) will preserve the brightness of the color but may change the hue towards the green

The toner cannot be stored and must be discarded after one printing session.