Etching of Damascus is done after manufacturing or grinding of the blank to bring out the contrasting steel patterns.
Be sure to always wear the appropriate protective gear when you’re working with acid. Complete etches in a well ventilated space and wear gloves, eye protection, and an apron or old clothes.
Muriatic acid is "hydrochloric acid" (HCl) in a less pure and diluted strength for non-technical applications like cleaning bricks. Ferric Chloride is an iron "salt" of HCl that is nonetheless very acidic, though not as "strong" as HCl.
Either will etch any high carbon steel, eventually. It is a matter of strength and timing. Everyone has a slightly different dilution and technique. The keys are "pretty dilute" and "multiple, short immersions". Wash the black oxide off between immersions and perhaps brush lightly with non-abrasive kitchen Scotchbrite or 800 grit paper. Dilution should best be done with distilled water to keep it uncontaminated with water minerals. Beyond that it's a matter of experimentation.
Ferric and Muriatic Acids work on Damascus Steels but will give 2 drastically different results.
Damascus Steel the two give much different results.
Ferric Acid will result in a double grey pattern (dark and light grey pattern) on either a matte or polished finish. Makes the material look like carbon steel Damascus.
Muriatic Acid will give a mirror/frosted finish on a polished finish and a lighter grey/grey pattern on a matte finish.
After being etched the blank can be polished to give a stepped or contrasting look.
This is for academic purposes only and should not be considered in any way a thorough instruction on this subject. There are significant risks to health and body including maiming and even death. It is the readers responsibility to seek out qualified instruction and to research all the health and safety risks involved and take the proper precautions associated with this activity.