# How can I safely carry out an electrolytic etch on stainless steel without producing relatively harmful by-products?

I propose to carry out an electrolytic etch on a stainless steel plate like so:

One of electrodes must be the stainless steel plate which is being etched and the surface layer must be removed.

I'm aware such an electrolytic etches can produce harmful by-products such as Chlorine (NaCl electrolyte), Chromium compounds and more.

If it is possible, What electrolytes and electrodes can I use to prevent the production of these substances?

Would it be possible to create safer Chromium compounds? If I can't, what other non-electrolytic options do I have?

• maybe titanium electrodes would solve for that ? – Adrian Suciu Jul 21 '17 at 14:54

$Cl^-/Cl_2$/ electrode has +1.36 potential, that is significantly higher that $Fe/Fe^{2+}$, so you can use $NaCl$ safely, as iron (and chromium) will oxidize before chloride-ions.

I doubt the electrolyte will have significant amount of $Cr(VI)$ as $Cr(III)/Cr(VI)$ potential is higher than for iron.

If you really care, threat waste electrolyte with Zn granules and then excess of $Na_2CO_3$ solution, collect the solid products and handle them as metal-containing garbage.

Sand or shot blast it instead. Rub it with crushed aluminum foil and saltwater.

Everything is harmful. Voltage determines products. Use the minimum voltage (slow way to travel). Don't use a chloride electrolyte. (TEST FIRST!) Use hydroxide, carbonate, (nitrate - Homeland Severity and OSHA will beat on you), sulfate, electrolyte (note solubility of metallic byproducts after reaction with electrolyte). The larger the charge on the ion, the slower the kinetics. Vent the chlorine plus inert air through lye solution to make bleach, or through a solution of reducing agent.

Cr(III) is OK, Cr(VI) is a carcinogen. Reduce spent electrolyte with sulfite, Vitamin C, zinc granules, FeCl2, shredded scrap iron, steel wool, etc - and have a way to test for Cr(VI) residual.

Before you vent or sewer anything, talk with your Safety Officer. The EPA and OSHA are carnivorous. it's always a good idea to be a good upstream neighbor.

• Thank you for that important info. I think I have come to the conclusion that stainless steel requires a bit more experience than what I have at the moment. What about a non-electrolytic etch for Aluminium using an aqueous Copper sulfate + Sodium Chloride solution. nontoxicprint.com/etchzincsteelaluminum.htm – suit Feb 18 '14 at 4:23
• Green Death solution in general, up to 90 C. You could add more copper and iron chlorides, more HCl, and some ntric acid for its oxidizing power. For shallow etches, metallographic.com/Etchants/Etchants.htm, metallography.org/EtchCD.htm – Uncle Al Feb 18 '14 at 20:07