– “Engraving.” Wikipedia, Wikimedia Foundation, 17 July 2021, en.wikipedia.org/wiki/Engraving.
– “Hand Engraving Tools.” GRS Tools, www.grstools.com/hand-engraving-tools/.
– “Laser Engraving Machines.” Epilog Laser Engraving and Cutting Systems – Etching, Cutting and Marking Systems, www.epiloglaser.com/laser-machines/laser-engravers.htm.