Need Help With Weird Acid Etch

[Lodato knives]

I dipped this knife I was working on in some 4:1 diluted ferric chloride from radio shack and got some strange effects in my steel. Its 1084 from Aldo that has been heat treated and finished to 800 grit. I can see that I have some sort of hamon looking effect which I believe is from my newer quench tank that is too small and possible only hardened the thinner sections fully. The thing I need help with is the funky patten that shows up in the steel when I etch it. It almost looks like the acid is pitting the steel. If this is the case im not sure why since it has never done this before. Any help on this would be greatly appreciated.

 

[Doug Lester]

I guess it is possible that you didn't have enough oil in the tank to absorb the heat from the thicker parts of the blade and caused differential hardening but my experience with Aldo's 1084 is that it doesn't do the hamon/differential hardening thing due to thickness well. It didn't do a great job when I clay coated one of my blades. The only thing that I can say is that if you feel that your new tank doesn't give you the volume you need to quench in then replace the tank with something that will hold more oil.

Doug

 

[Lodato knives]

Thanks Doug for the reply. I had a feeling that my quench tank may be the cause of the differential hardening I see and I am going to replace it. Along with that though, there are streaks of darkness that are horizontally across the blade. Im thinking that my acid is contaminated somehow and could be causeing an uneven etch and pitting the steel. Could it also be an issue with the steel?

 

[wall e]

I use a 3 to 1 solution for my pcb and have it about bath water temperature and, get some nice dark solid color. Some times I have striped portions of a blade show up as well but they are highlights of the fine sanding scratches that didnt get cleaned off. It stopped when I used an old tooth brush and a watery baking soda paste to clean and neutralize the etchant.
Here is what I get with the 3 to 1 an a 7 min soak at bath water temp.

 

[J. Doyle]

There could be a lot of things going on there. It's actually hard to tell from the pics because, as you mentioned, the blade looks streaky and splotchy.

A knife about to be etched needs to be INSANELY clean, free from all grease, oil, dirt, dust, fingerprints, solvents and cleaners.

Also, the finish AFTER the etch needs to be really clean to properly assess if the effects you are seeing are due to the quench and are indeed a by product of some sort of differential hardening, or if what you are seeing is scale or decarb or something else involving the etchant itself or some residual effects of a hiccup in the cleaning etching process.

Honestly from the pics, its hard for me to tell what, if any, of that might be the case.