Question about ferric chloride

[Laredian]

I have a question for you fine gentlemen. I have been using ferric chloride to etch my blades for a while now. For some time my thing was doing a two tone finish like this:

Now I've been experimenting with stonewashing or acid washing and after some time I started getting decent results:

Now my question is this: is a blade like that kukri safe for food preperation? The knife is clearly not designed for food prep, but if I were to make a smaller blade with the same finish I'd like to know it is safe for use in the kitchen.
I am asking primarily because if I wipe down that kukri with some ballistol the blade still gives off a bit of black residue, which I can only assume are black oxides from the etching process. I neutralized the blade after the etch though, so I'm not sure if this is a normal phenomenon or if I made a mistake in my process.

 

[Stacy E. Apelt - Bladesmith]

The dark spots are just iron oxides. There is nothing unsafe about it. The oil you put on the blade should be washed off if used for food.

 

[HSC ///]

The dark spots are just iron oxides. There is nothing unsafe about it. The oil you put on the blade should be washed off if used for food.

further on the use of FC...

1) I think mine is getting old and muddy looking after regular use for a couple years,
How often do you suggest changing it out?

2) how to dispose of the old FC?

thanks

 

[gammarad]

(...)
2) how to dispose of the old FC?
(...)

If you only used it for carbon steels (no Ni, Cu or Cr in the solution, dilute it 100:1 and use it as a fertilizer on your garden.

 

[Stacy E. Apelt - Bladesmith]

Yup, I set a big tub out by the garden, dump in the old FC and sludge, and run the hose in it for a ten minutes. It would also work to dilute it (say, 5:1) and spray with the hose sprayer (like the ones to spray Miracle Grow) on the grass ... the iron would make the grass super green.

I make 42° Baume stock batch about every year or so and use it to top up the etching tank as needed. Whenever the etch seems odd or it starts taking too long, I dump the etch tank as above, rinse the sludge out, and mix up new 3:1 solution using the stock solution. I have never seen any issue no matter how old the unused stock gets. Store the stock solution in a cool place out of the sunlight.

BTW, TSP makes a great neutralizer. You can make up a tank of it and after rinsing the blade off with running water, soak the blade in the neutralizer tank for 5 minutes. A tank full of Bo-Peep ammonia will do the same.

TIP:
For a great etch tank, use a 24" piece of 4" PVC pipe. Use a closet flange for the bottom and attach it with plenty of heavy duty PVC cement. For the top use a PVC cap. Screw the foot plate to a 12"X12" piece of plywood (square or a 12" circle) for stability and safety. Now, here is the really great part of this tip - take a 2" section of PVC pipe that is smaller than the tube and cut it in half making two semicircles. Sand the ends so the seat against the cap properly, and cement them in place with heavy duty PVC cement. Let it dry at least a day, then apply some extra cement. After drying a couple days more the cap will now have handles you can grab to twist it off. If the cap is too tight, sand the top of the tube with 400 grit paper to make the fit looser.
Pipe - $10 - https://www.homedepot.com/p/VPC-4-in-x-24-in-PVC-Foam-Core-Sch-40-Pipe-2204/202300523
Closet Flange - $5- https://www.homedepot.com/p/Water-T...nge-for-3-in-or-4-in-PVC-Pipe-86132/203593716
Cap - $10 - https://www.homedepot.com/p/4-in-PVC-DWV-Hub-Cap-C4817HD4/205799563

 

[Cushing H.]

What do you do if it was used to etch stainless?

 

[Stacy E. Apelt - Bladesmith]

It is pretty much the same as etching carbon steel. The main thing dissolved is iron. The only other thing FC eats away is copper/brass/bronze.

 

[Cushing H.]

It is pretty much the same as etching carbon steel. The main thing dissolved is iron. The only other thing FC eats away is copper/brass/bronze.

So it can still be used as fertilizer? Cool

 

[Stacy E. Apelt - Bladesmith]

I don't see why is couldn't.

 

[nerdlock]

Hi everyone!

This being a ferric chloride questions thread, I was wondering if acid etching and stonewashing blades would affect its sliceability?

I mean, since the finish gives the surface of the blade a rough matte texture, wouldn't that create additional friction when slicing stuff like paper, cardboard,etc.?

Apologies if the question seems dumb, a quick google search didn't give anything.

 

[Stacy E. Apelt - Bladesmith]

I doubt anyone could tell the difference. Technically, a pebbly surface has less friction.