- An orange-red crystalline compound, C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>, used as an acid-base indicator and in making dyes.
- Commercial alizarin is sold in the form of a yellow paste containing 20 per cent. of dry substance, and, less frequently, as a dry powder. The dry substance in the paste is seldom pure alizarin, but contains varying amounts of flavopurpurin and anthrapurpurin, both of which have properties similar to alizarin. Natural alizarin derived from madder contains purpurin in addition to the above. The nature of the various commercial alizarins is often designated by suffixed letters or numbers. Thus <em>alizarin I, alizarin P</em>, and <em>alizarin V</em> are nearly pure alizarin and give blnish reds, while <em>alizarin CA, alizarin G</em>, etc., contain anthrapurpurin or flavopurpurin, or both, and give yellowish reds.
- A peculiar red coloring matter (C<sub>14</sub>H<sub>8</sub>O<sub>4</sub>) formerly obtained from madder, and extensively used as a dyestuff.
- A coloring principle, C14H6O2(OH)2, found in madder, and now produced artificially as an an orange-red crystalline compound from anthracene. It is used in making red pigments (such as the Turkish reds), and in dyeing.
- a type of <xref>red</xref> or <xref>crimson</xref> <xref>dye</xref>
- an orange-red crystalline compound used in making red pigments and in dyeing