Alizarin: a mordant dye

Alizarin is the synthetically produced varient of madder, which can be used to dye fabrics, especially cotton, red. A metal ion known as a mordant reacts with the dye making a structure held together by relatively weak chemical bonds and the colour of the dye is dependent on this mordant. Common mordants are aluminium (Al3+), iron(II) (Fe2+) and barium (Ba2+).

  • In order to dye with alizarin, the cotton must first be soaked in an alkaline solution so that the mordant can bind with -OH groups in the fabric.
  • The fabric must then be placed in a solution containing the mordant.
  • Finally, the fabric must be transfered to a solution of alizarin.

  • The structure of Alizarin

                       OH       OH
                        \      /
                 O       C == C
                 \\     /      \
         H        C -- C        C -- H
          \      /      \\    //
           C -- C        C -- C
          //    \\      /      \
    H -- C        C -- C        H
          \      /     \\        
           C == C       O        
          /      \
         H        H