Gultom, J. et al. 2017. The extract salaon (Indigofera tinctoria L) leaf as the natural dye of ulos in keeping for the batak culture values. Jurnal Pendidikan Kimia. 9, 2 (Aug. 2017), 293–298. DOI:https://doi.org/10.24114/jpkim.v9i2.7602.