Pigments through the Ages

              
/ pruh • shun   bloo /
Prussian blue 
 
   

     
 

  1.  Overview  
  2. History
of use
 
  3. Making the
pigment
 
  4. Technical
details
 
  
  How Prussian blue is made:
        
Artificial variety of pigment
Precipitation from the solution of potassium ferricyanide by a more saturated solution of iron(III)-chloride.
19th century recipe
Dissolve sulphate of iron (copperas, green vitriol) in water; boil the solution. Add nitric acid until red fumes cease to come off, and enough sulphuric acid to render the liquor clear. This is the persulphate of iron. To this add a solution of ferrocyanide of potassium (yellow prussiate of potash), as long as any precipitate is produced. Wash this precipitate thoroughly with water acidulated with sulphuric acid, and dry in a warm place.
In the lab
Materials needed:
potassium ferricyanide and iron(III)-chloride.
Safety (MSDSs):
Method:
A solution of 2 g FeCl3 in 100 ml deionized water is slowly poured into a stirred solution of 1 g K4[Fe(CN)6] in 200 ml deionized water. The blue precipitate is filtered and dried at elevated temperature (c. 100°C)

  Illustration of the process:   
        
Making prussian blue in the laboratory:
Solutions of potassium ferricyanide and iron(III) chloride are poured together    
Solutions of potassium ferricyanide and iron(III) chloride are poured together

Filtration of the resulting precipitate of the pigment prussian blue
Filtration of the resulting precipitate of the pigment prussian blue

  The ground pigment:   
        
Pile of ground Prussian blue:


Other blues        
(intro) - Azurite - Cerulean Blue - cobalt blue - Egyptian blue - Indigo      
Prussian blue - smalt - Ultramarine        

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