Introduction: Acid/Brass/Stone Washing a Knife

Picture of Acid/Brass/Stone Washing a Knife

For my first Instructable, I thought I would lay out a step-by-step guide to creating a one of a kind look for any knife. This will work for any knife (actually any item made of steel!), so long as you have large enough containers to fit them in.

Step 1: Safety Notes!

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DISCLAIMERS: Don't do this kind of stuff at home if you don't have a basic understanding of high school chemistry. You will hurt yourself BADLY, and I won't be held responsible. Legalese out of the way; onward!

Safety first, you are working with dangerous chemicals.
1. Goggles, eye protection: wear them.
2. Gloves: get some. No vinyl, acetone will melt it. Nitrile is good, rubber is better.
3. Respirator if you have one, the fumes from this procedure can be quite irritating. You may want to complete this outside if you do not have a well ventilated room. Do not purposely inhale the fumes. Don't quote me, but I have read the fumes may contain chlorine gas amongst other things, and chlorine will kill you in high enough doses. Be smart.
4. All bowls, containers, measuring tools, and funnels must be glass or plastic. Metal will corrode!

Another IMPORTANT note, this will void any warranty you have. I'm not responsible if you attempt this and dissolve your blade. Pay very close attention to the timing of your acid bath, and don't etch screws. The acid will eat the threads, and then you're the one who's screwed.

You will also need to sharpen your blade when all is said and done with your desired sharpening methods. These are like fingerprints and snowflakes, extremely individualized, so I won't touch on sharpening much.

Step 2: Required Chemicals & Must Haves

Picture of Required Chemicals & Must Haves

Gather your chemicals. You will need:
1. Muriatic/hydrochloric acid. This is available at almost any hardware store, it is used to clean concrete, and adjust pH of pools.
2. Hydrogen peroxide, the 3% from your local pharmacy is fine. Higher percentages will work faster, and are available at any cosmetic supply store or online.
3. Acetone, used to clean and remove oils from all metal surfaces.
4. Nail polish. This is used as an acid resist, color doesn't matter but I do recommend black or red as it is easier to see and thus remove later.
5. I use the reinforcement stickers as stencils for cleaner lines when applying resist.
Not pictured but also required:
6. Baking soda, this will be used to neutralize the hydrochloric acid etchant.
7. A plastic/glass measuring device, and plastic funnel. Do not use metal as they will corrode immediately.
9. Tumbling "media" and tumbler. Here you will need some type of plastic jar or bottle, I choose to use a 32oz Gatorade jug. You can also use a mayo or peanut butter jar. For media, you will need either a.)7-12 thumb-sized smooth rocks (these can be from a local brook/river or the craft section at Wally World), or b.) +/-50 pistol brass cases, in this case 9mm.
10. WD-40/PB Blaster (any aerosolized petroleum-based oil will probably work) or water and dish soap.

Step 3: Disassembly

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Starting with a bone stock knife, you will need to disassemble it completely. A Spyderco Tenacious and Kershaw Chive are both used in this Instructable.
Be sure to separate all screws, standoffs, springs, etc into a secure container. In one photo, you can see I have already begun applying my "resist", the nail polish.

Step 4: Cleaning Parts to Be Etched.

Picture of Cleaning Parts to Be Etched.

Once disassembled, put on your gloves and glasses, and clean all parts thoroughly with acetone. You must remove all oils from the parts or it will result in a poor etching! From this point on, do not touch any parts without gloves.

Step 5: Applying Resist.

Picture of Applying Resist.

Change your gloves at this point if using nitrile. Nitrile has a "fair" resistance to acetone and at this point is probably at breakthrough.
Apply nail polish/resist to all parts you do not wish to be etched. I recommend using some type of stencil, such as the reinforcement stickers, to keep your work more professional. As you can see, I did not use them on the Chive, and I feel the results suffered.
You will want to pay very close attention to the detent, lockbar surfaces on the liner and blade, the pivot and thrust areas, and all screw holes. Make sure all threads and hole edges are thoroughly painted, even using 2-3 coats. The tolerances on most high quality knives are so close that even the microns removed by the acid can result in changes to the knife's geometry, resulting in "lock rock" and poor action. Change gloves as necessary to avoid getting any "resist" on areas it shouldn't be.

Step 6: Acid Etching

Picture of Acid Etching

Using a bamboo skewer and some wire (a chain of plastic coated paperclips is better, they won't be dissolved like the wire), fashion a hanger that will allow you to place the parts to be etched in a glass container. Here, I am using an old food jar, but you can also use a flower vase or other glass container. In the photos you will see I have placed the jar in a larger bowl, and surrounded it with baking soda. Baking soda will neutralize any spills.
Using a plastic/glass measuring device and funnel (metal will corrode immediately), add two parts hydrogen peroxide, and slowly add one part muriatic acid to your etching container, and always remember AA: Add Acid. Do not add H2O2 to HCl. The reaction is exothermic (produces heat) and can be violent if you do it wrong. Always add the acid to the hydrogen peroxide! The solution will begin to turn green as it contacts the steel.
Pay attention! The reaction is fast, check every minute or so till it reaches the desired darkness. In the case of the Kershaw, I only etched it for five minutes, the Spyderco was etched for a timed twenty minutes. In reality, with this etchant, more than ten minutes is probably unnecessary.
Something to note: different steels will react to the acid in their own ways. Some will darken more, some cheaper steels will pit and nearly dissolve completely. Heat treats can affect how the steel takes color, with raw untreated steels typically staying lighter. This will affect many fixed blades, as some do not quench the tang, giving it different properties. Pay close attention to unmarked or lower quality knives so you don't destroy them.

Step 7: Neutralizing Acid.

Picture of Neutralizing Acid.

Once the desired time and/or darkness has been reached, I recommend placing the parts immediately into near boiling water. This is a step I use while acid/rust bluing gun parts and results in a darker etch, and helps to "lock" it in. After 30 seconds to one minute, remove the parts from the water and neutralize any remaining acid with baking soda. Any acid will bubble just like the volcano you built in middle school for the science fair. Once neutralized, rinse with clean water and dry thoroughly. VERY IMPORTANT: You must neutralize the acid using baking soda (or ammonia/Windex if you can monitor pH to a neutral 7.0). Failing to do so will cause rusted blades, chemical burns, and general stupidity. Maybe your first born will have a tail, I don't know...

Step 8: Clean Up.

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At this point I recommend starting your cleanup. The etchant you mixed can be stored in a plastic container and used indefinitely. It can be renewed by simply adding air using an aquarium pump. Please mark your container well and cover tightly to avoid accidental ingestion or other mishaps. All jars, bowls, and measuring tools must be neutralized with baking soda and rinsed thoroughly!

Step 9: Completing Your New Look.

Picture of Completing Your New Look.

After neutralizing, you need to decide your next step. You can oil your blade and leave it as is with your new, darker finish, or take it a step farther.
Shown here are both methods I have used. The methods are the same, the only difference is in the media used. You will place your parts one at a time (one part per cycle, very important as the steel on steel can result in damage!) in your "tumbler" and add your media. You can use stones or brass cases. Once this is done, give everything inside a very liberal spray of WD-40/PB, or a mix of water and dish soap (Tablespoon total?). Close up your container and tape it shut.

Step 10: Tumbling

Picture of Tumbling

Two options here.
1. Shake the jug until your arm falls off (may result in a more uneven finish), or
2. Wrap your jug in a towel, tape it up (picture is really overkill, one wrap around will do), and place in a clothes dryer. Tumble on Fluff/No Heat setting for 10-20 minutes. Ten minutes results in a light pattern, twenty obviously will be heavier.

Step 11: Cleanup and Assembly

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All pieces must now be cleaned of any remaining resist, and grime from your tumbling media. Skipping this will leave you with a very "gritty" knife, one that doesn't open properly. Begin by rinsing thoroughly with soap and water, cleaning off the oils and dirt. Using fresh gloves and acetone (don't NEED gloves at this point, but acetone can be very drying to your skin), remove all traces of nail polish using paper towels, Q-tips, whatever you have handy. Go ahead and reassemble the knives. Check your pivot for that gritty feel, if it's there, take it apart and clean again. Once you have it all cleaned up, I recommend threadlocker (medium/blue?) on all screws, but some will say it's sacrilegious. Adjust your pivot screw to your preferred opening tension, and verified blade is centered. Allow the correct amount of time for the threadlocker to set.

Step 12: Sharpen and Enjoy!

Picture of Sharpen and Enjoy!

Obviously acid and tumbling will kill your edge, so at this point it will need to be refreshed. You can choose to do this before assembling the knife, entirely up to you. Your bevel should still be solid, so a few quick passes at a lower grit are all that's necessary to break through the finish, followed by higher grits and so forth. I use a Gatco Professional diamond system followed by stropping on canvas, rough leather, and smooth leather (50 laps each) to get that hair popping edge. You can use your preferred method of course. You can protect your new finish with electrical tape if you're using a clamp system like the Gatco, Lansky, Apex, etc.
Finally, it's time to enjoy having the coolest knife on the block! Unless of course you have awesome neighbors who like knives as much as you...


joe_blade (author)2017-09-27

Nice detailed instructable. Have you ever considered using ceramic media for stone washing? Works excellent!

Nishidake (author)2015-11-06

What a fantastic 'ible! I love that it uses mostly stuff I already have around the house. I will definitely be doing this!

Questions: I'm not a gun person and I don't have access to spent shells. Would this work the same way with some assorted brass nuts/small hardware? What about copper? Does it react with the acid used? Also, sorry if this is a question that shows my firearm ignorance, but if I went to a shooting range and asked nicely, do you think it's possible they would give/sell me some spent shell casings? I'm thinking of how some bike shops will give you free busted innertubes if you ask.


mbeachboy16 (author)Nishidake2015-11-10

usually a range will sweep up loose shells and bag them and sell them cheap for people to use them again in "reloads"(ammo that people reuse the casing). but u can ask for "rimfire" shells. these shells cant be reused and are pretty much trash.......there usually small .22's and i believe thats what brokerolla used on the spyderco. good luck.

brokerolla (author)mbeachboy162015-11-10

Ranges near me only sell wholesale, so that's cool if others allow you to buy. I actually used 9MM brass, I don't even take the time to police up .22LR shells... :)

brokerolla (author)Nishidake2015-11-09

The assorted brass hardware would work absolutely fine! As for copper, I personally haven't done it, but it is softer than steel so should work great. Let us know anyways! As for the reaction with acid, as long as the knife has been washed thoroughly with water, or neutralized with baking soda, no acid should remain. On the topic of gun range brass, it can't hurt to ask, but most gun owners clean up their own for reloading or recycling for money. I know the ranges I frequent tend to resell to recyclers anything that they sweep up from left behind cases, so I doubt you'd get them free. The brass nuts would be a much better option due to size, and probably less costly to be honest. I simply used brass cases because I happen to have them in a box.

mbeachboy16 (author)2015-10-29

this feels like a dull question but can u use this etch solution over paint? like a factory black tenacious blade? will it just eat it away? or must i remove it first

brokerolla (author)mbeachboy162015-11-09

Not sure what Spyderco uses for a finish on their black blades. If it's anything like a Boker or CRKT knife or some pistols, it's probably an electrofinish or baked on. In that case, I doubt it will work since the finish will act as a resist.

43totheN (author)2015-04-24

Very interesting. Do you notice a difference between using stones vs shell casings for tumbling media?

brokerolla (author)43totheN2015-04-24

They actually result in a completely different look. The stones result in a gray/black blade, whereas the brass is a black/gold. I prefer the shells, as the finish seems much more even and can get in closer to the choil and other smaller areas the rocks miss. Also, significantly easier cleanup. The Kershaw had to be cleaned three times before all the grit was out. I can't seem to load a photo here to the comments, so I'll add one to Step 12 showing side-by-side the difference in the two finishes.

mbeachboy16 (author)brokerolla2015-10-26

great read:) thanks alot. what specific resist did u use? and did u use .22 casings? thanks for your time

brokerolla (author)mbeachboy162015-10-26

I used black nail polish I robbed from my stepdaughter as a resist, works great. As for the casings, I actually used 9mm because it was what I had on hand. .22 would work great as well. I will say, if you use the knife a lot, the brass will wear off fairly quickly. I tend to be pretty roughon my knife, and the brassing wore off after about three months. I enjoy the look of the plain acid wash just as much though.

mbeachboy16 (author)brokerolla2015-10-26

thats easy n cheap! great news. so it just looked like an acid wash after it wore off?

brokerolla (author)mbeachboy162015-10-26

Yep, just regular acid wash.

LeviV1 made it! (author)2015-09-10

my first acid stonewash. My Kershaw had seen better days, she was scratched to hell from learning to sharpen with shapton whetstones. Now has a beautiful even coating. The coatings I've seen were uneven and a little ugly, so the thing I did differently was with the stone part. In the dryer I had the package taped down to the drum so the contents only moved, not the whole package. And along with thumb sized stones I added a handful of small pinky nail sized stones. It resulted in a great even coating that I think is better.

LeviV1 made it! (author)LeviV12015-09-10

she isn't sharp yet, but tomorrow morning she'll be ready to shave some faces.

rkutchinsky (author)2015-06-25

i really liked this instructable, i do however have a safety note.
instead of using baking powder or another alkaline substance to neutralise the acid, simply wash the knives in clean water for a minute or two, this will cause a much less violent reaction, and is thus safer. Also, you will be able to reuse the acid :-)

keep up the great work!

tkalko made it! (author)2015-06-15

Excellent ible, very easy to follow and well written

I also used protective coating on the edge itself, in order to preserve as much cutting edge as possible for the edge loss during resharpening to be as small as possible.

Jthooghouse.aia (author)2015-04-25

This is an excellent instructible! I'm on it! Taking my tinkering to another level! Thank you! Any luck with positive or negative logo stencil application? Assume what they are made of would be important!

I have not personal done any logos, however, many guys (and gals!) in the custom knife scene have. They're as simple as making your stencil, applying it, and filling in the parts you don't want etched with a resist (nail polish again!). I would think a printer and some type of sticker paper might work, cutting them individually with an X-acto or scalpel? Might be worth the time saved and precision of having custom stencils done at a sign shop if you're doing a lot of logos. Many will even draw designs or splatters on the blades before etching for a unique look. Basically anything you don't want etched can be covered with the resist, be it a design or logo. As always, the better your prep, the better the final result.
The photo isn't mine, but just an example of the possibilities.

GrfxGawd (author)brokerolla2015-05-02

For easy breezy stencils cuts invest in a Silhouette Portrait or (as I own) Cameo. You can cut vector art into vinyl and apply directly, or use frisket to mask and apply your resist. You can use the vector cutters for everything from custom apparel and hand craft to making circuit boards or designs/logos/SN's on anything that will etch via chemicals or with abrasives. I made a custom vinyl decal for my mother's Sorentos back window, she loves it! She's the only one in the world with one on their car. The potential uses for vector cutting materials is so diverse it's staggering... And they market these things to housewives for making doilies, scrapbooking, and personalized greeting cards - such a waste.

Jake_Makes (author)2015-04-24

Awesome project, could you do the same kind of thing with vinegar instead of the chemicals?

hlamer26 (author)Jake_Makes2015-04-28

Could you let me know what you find out if you do find any info? Thanks.

brokerolla (author)hlamer262015-04-28

Few different methods after a search on a few custom knife sites.
1. Boil and reduce four gallons of white vinegar down to one gallon, and allow to cool to room temp. Immerse the items in the reduced vinegar (supposedly now has a higher acid percentage, don't know how accurate this is) and remove the oxides every six hours or so until you reach desired darkness. This works best on carbon tool steels like 1095, and can take 36-48 hours.
2. Boil white vinegar and immerse the items in the vinegar bath, preferably in a glass container. Place the item in an oven on warm setting, check every couple minutes. I've read everything from five minutes to 24 hours on this method, but some very big names in the custom knife world say hot vinegar works as fast as HCl (the method in this Instructable).
3. Room temp vinegar, ~24 hours.
All of these will require you to neutralize the acids with baking soda or Windex (ammonia), and clean off the oxides with 0000 steel wool before oiling.

Jake_Makes (author)brokerolla2015-04-29


Jake_Makes (author)hlamer262015-04-29

Sure, as soon as i get around to it. The reason i thought it would do something like this is because I have soaked metal in vinegar before, to be able to clean off some stuff on it. (old saw blades mainly) And it always came out with a darker, grayish finish, the longer the darker. I always wondered if i could get a poor man's stonewashed finish with it.

I would use chemicals, but I don't have them handy and I try to do all my projects for free. :)

brokerolla (author)Jake_Makes2015-04-24

You can, although I have no experience with it. I believe you need to boil the item in vinegar for an extended period, but a quick internet search might turn up more detailed instructions.

Zaphod Beetlebrox (author)2015-04-24

Will pitting the surface like that not lead to significantly increased rust/tarnish? How long until the (oxides?) darkened colour wears off?

As long as the steel was in good condition before, it should not pit and you'll still have a smooth surface. The rocks and brass used are both softer than the steel, and also do not pit it, rather they leave only a surface treatment. I'm sure some type of solvent could easily remove the brass, but the dark acid color is there to stay.
As I understand it, the darkened color is not just a surface treatment, it is actually identical to the acid etch used for adding logos (not electroetching), and sits "deeper" in the metal. This process was originally used to treat gun parts long before modern hot salt bluing. Many blackpowder rifles from the 1700-1800s (and earlier) were blued using this method, and still remain in immaculate shape today. From my previous research, the boiling water dip chemically changes the oxidized surface. I don't remember the exact molecular change, but this is how it was done for hundreds of years. The basics of rust bluing are: steel is coated with an acidic pickling solution, allow to rust for 24 hours, dip in near boiling water for a minute or so. The red iron oxide will then turn black and can be carded off with 0000 steel wool. You repeat the process five to seven times, and you have a traditional bluing. This is still the only way to blue vintage shotgun barrels with lead soldered ribs, as modern hot salt methods will melt the solder. I have restored multiple shotgun barrels this way, and all came out wonderful.
With the knife, we are just speeding up the process by using the hydrogen peroxide. You could theoretically mix the HCl 50:50 with isopropyl alcohol and apply it to the knife, allow to rust overnight, dip in boiling water, and get a similiar result. I have not tried this with a knife, but it should work beautifully on carbon steels like o1 or 10xx. This is similiar (actually almost identical...) to the method used to etch Damascus, as the different steels will react in their own way, resulting in the patterns seen in Damascus steels.
Anyways, completely off topic way of saying the finish should last a lot longer than most people will keep a knife. If anyone understands it differently, or my recollection is wrong, please let me know!

brokerolla (author)brokerolla2015-04-24

Totally left out the rust question... The resistance to rust is a property of the steel itself, and is not changed by this process. If you begin with a stainless steel, you still have stainless, and vice versa with carbon like o1 and the 10xx steels. I always recommend keeping a blade lightly oiled no matter the steel composition, using food grade mineral oil (especially if knives will be used to cut food).

Ok so if I am understanding this correctly it does help the knives(gun barrels) resist rust, but not much. The primary purpose is to stop iron oxide (red rust) from forming and continuing to eat away at the steel until it flakes off. Instead you get this blue rust which sticks to the steal but doesn't continue to react with it.

Is it still food safe?

Is tetnis still an issue?

Also thank you for publishing this, and your excellent comments. If the above is true I will do this to my knives.

Bluing really applies to any steel, but especially carbon steel knives. The magnetite formed is an oxide, but rather than eating away at the steel like red rust, it converts any red rust simply to more blue-black magnetite. This helps carbon steels resist rust well, but it certainly won't put it on the same level as stainless. I have yet to make any of my own knives, but I am building a gas forge and plan to in the next few months, and will be experimenting with bluing my knives using this method.
If you apply a food grade mineral oil, like one would when caring for any high end carbon kitchen knife, it will be perfectly fine for food. It's also great for wood handles.
As for tetanus, I honestly don't know. Maybe someone with a medical background will chime in?

plantprof (author)brokerolla2015-04-27

Tetanus is caused by an anaerobic, spore-forming bacterium that is found in soil and some animal feces, particularly horse manure. The spores can resume growth ['germinate'] in conditions ideal for the survival and growth of the living bacterial cells, such as puncture wounds that exclude oxygen [anaerobic]. The common idea that rusty nails cause tetanus is true only if the nail is contaminated; the spores, not the rust, cause the disease. A brand-new nail [or anything that can puncture skin] is just as dangerous if contaminated. Rusty nails have probably been exposed longer in dirty environments and have a greater chance of being contaminated with tetanus [Clostridium tetani].

Thanks, thought it grew in rust. So they should be food safe then.

Wow thanks for the excellent response. What is the purpose of the blueing, or is it purley cosmetic?
The boiling water is neat and explains why sometimes my carbon steel knives are more difficult to clean. I'll be sure to only wash them in cold now :)

So I pulled out a few older books and did some more research today so I could better understand the chemical reactions. Of all the bluing methods, including hot, salts, cold, caustic, etc.; the consensus is that rust bluing provides the best rust and corrosion resistance as the process continually converts any metal that is capable of rusting into magnetite (Fe3O4), the black oxide of iron. The step of boiling converts the outer layer of red rust Fe2O3 to magnetite, creating a permanent outer layer of corrosion resistance. It still needs to be treated with a water-displacing oil for maximum protection.

brokerolla (author)brokerolla2015-04-24

Just an example of the finish possible with rust bluing. The photos here show a barrel that has been sanded to 400 grit, followed by cleaning with acetone to remove oils and fingerprints. A rust blue solution (50:50 HCl and isopropyl alcohol, with enough steel wool dissolved into the solution the acid won't dissolve anymore) was then applied and allowed to sit overnight, followed by a boiling water bath. This procedure was done five times on this barrel, between each rust blue application the barrel was carded off with 0000 steel wool. The resulting finish is shown last.

ksoem (author)2015-04-27

Looks nice.

It could be mistaken for Damascus blade from a long distance.

samalert (author)2015-04-27

A very innovative way of doing stone wash. I have seen stone washing in factories "How its made" but this was one of the very "JUGAD" (Hindi-Urdu Indian LINK) way of accomplishing task.

BeachsideHank (author)2015-04-26

Don't try this with the "Boowie" read "Bowie", Katana, or the "Highlander" blades you buy from "The Knife Show" at 2:00 a.m., unless you like chemical soup. ;-)

Really though, a great dissertation on this secretive process.

brokerolla (author)BeachsideHank2015-04-26

Agreed, you would definitely want to start with a knife of decent quality to begin with. The Tenacious is perfect for this process, although it is made in China (not a bad thing, even though others would say it is), it is made to Spyderco's quality control specs from 8Cr13MoV, the Chinese equivalent of Aus-8 (a fairly respectable steel). You can pick them up online for ~$35, so don't think you need to spend a lot for a quality blade.

Odie Sr.O (author)2015-04-26

Instead of using special hangers for the acid bath, try monofilament plastic fish line. . . Works like a charm. . . Nice project. . .

brokerolla (author)Odie Sr.O2015-04-26

Awesome tip, thanks!

aebe (author)2015-04-26

Looks to be a very nice finish , I will be giving it a try .

Tetanus , or any other disease organism , are easily dealt with just by keeping your fixins clean . :)

nliwilson (author)2015-04-26

very nice instructable, thanks. :)

raptor_demon (author)2015-04-24

Very cool, never knew how this was done!

Jobar007 (author)2015-04-24

That's a really neat look that you've created there. Easily repeatable and well documented. Thanks!

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