Sari, sinta widya et al. 2025. The Effect of Variations in Cocoa Shell Carbon on the Characteristics of Environmentally Friendly Stamp Ink. Jurnal Phi : Jurnal Pendidikan Fisika dan Fisika Terapan. 11, 1 (Jan. 2025), 45–51. DOI:https://doi.org/10.22373/p-jpft.v11i1.20137.