Acid Etch Stainless Steel

This was an experiment to darken stainless steel. Regular carbon steel acid etches well, but stainless is much harder to darken. As I use mostly CPM154, 154CM and AEB-L stainless cutlery steel, I am looking for a way to darken a blade. In the case of carbon steel the etching provides protection for the blade from corrosion. In the case of stainless steel, which is already protected, acid etching provides darker aesthetic coolness.

How to get the blade to go dark? Soaking in some acidic solution is the way, but what solution will work and where can I find some? Vinegar is typically 5% to 8% acetic acid and while it may seem like a good place to start, but my initial experiments show it doesn't impact stainless very much. I guess this is why it is called STAINLESS STEEL!

My experiment is with Chemtec 'Sparkel' brand toilet bowl cleaner which contains hydrochloric acid.

This experiment deals with chemicals that can cause burns.
Always wear gloves, skin and respiratory protection. 

The MSDS clearly spells out the recommended here: Chemtec Sparkel Material Safety Data Sheet

The brand I chose which was readily available at Canadian Tire and about $6 a litre (909 ml). The MSDS states this is between 10 and 30% hydrochloric acid, which is a pretty broad range, so I have to estimate this be 20%. Having used this product for cleaning before I know it's quite strong.

I have a heat treated AEB-L blade from a scrapped project that I will submerge into the acid and measure the temperature and time it takes to darken the blade to various levels of grey. I am doing this in my garage the temperature is what it is. Heating the solution will increase the effective etching and reduce the time it takes to achieve a certain level of greyness.

My garage is well insulated and stable in temperature fluctuations, but cool this time of year, so the ambient temperature is about 12°C (53°F). The solution is the same temperature as ambient.

Checked after about 24 hours. 12.5°C.  I think this will be dark enough to stone wash in the tumbler.

The solution has changed from pink to light green. I cleaned up the blade with fresh water.


Warm acid to speed up the etching. Admittedly, my garage is cool. I wouldn't recommend doing this in the house though, it does smell a bit and the risk of spilling makes it better suited to ventilated garage or preferably outside.

Further exploration:

Ferric Chloride
Nitric Acid


alfanje said...

great tutorial !! thanks friend

Gabroo said...

fine site

eutrophicated1 said...

20-30% hydrochloric acid is very strong and will burn skin in a hurry. Nitric acid will too.

Most important: Never combine hydrochloric and nitric acids, as they make what is known as aqua-regia, a most dangerous acidic chemical. The fumes alone can damage lungs severely.

D. Comeau said...

True. Same can be said about mixing acid and bleach and liberating chlorine gas.