Haematoxylum campechianum was used for a long time as a natural source of dye. The woodchips are still used as an important source of haematoxylin, which is used in histology for staining. The bark and leaves are also used in various medical applications. In its time, it was considered a versatile dye, and was widely used on textiles and also for paper. The extract was once used as a pH indicator. Brownish when neutral, it becomes yellow-reddish under acidic conditions and purple when alkaline. In a small demonstrative experiment, if two drops, one of concentrated ammonia and one of logwood extract, are placed close enough, the NH3 vapours will change the color of the extract to a purple shade
