The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Al etch soot removal

I am caustic etching small aluminium parts but the 'soot' residue does seem difficult to clear. I have tried white vinegar ⇦in bulk on eBay or Amazon [affil links] (acetic acid ⇦ this on eBay or Amazon [affil links] ) but this doesn't seem to work well. Should I use a stronger acid like Hydrochloric. ?

Gordon S. BRADLEY
Hobbyist - Wellington, NEW ZEALAND
2005

---

That won't work either, Gordon. What happens when you etch aluminum is the surface becomes enriched with the alloying ingredients like copper and silicon that didn't dissolve when the aluminum did. These smuts are difficult to remove and require acids like nitric and hydrofluoric respectively. Nitric is nasty; hydrofluoric terrifies the professionals. You would be better off minimizing any caustic etching you are doing, or sending the parts to a shop for desmutting.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

---

2005

Thanks for the reply about Aluminium caustic soot.
I tried a solution of nitric acid which solved the problem.
Brad.

Gordon Bradley
- Wellington, NEW ZEALAND