Science teaching festival
From Madder to Alizarin
Obtaining one of the pigments used by the painter of "Pala di San Bernardido", starting from madder roots, a common plant all over Europe.
Alizarin extraction: The alizarin content of the roots depends on the season and on the kind of soil, although the average content is about 1.9% w/w. Soak x g of dried madder root in 0.27 M hydrochloric acid solution (HCl) for 48 h at room temperature. Remove the roots and dry them. Add 1.9x mL of alum solution at a concentration of 0.021 mol/L. Boil the mixture for 3 h, keeping the volume constant by adding small quantities of water. Allow the mixture to cool and separate the roots from each other. Dropwise, add 0.63x mL of soda at a concentration of 0.094 mol/L to the solution. Once the pigment has precipitated, collect it using a Buchner funnel, and rinse and dry it.
For more information see: www.scienceinschool.org/2006/issue1/francesca/.