First attempts at Acid Etching

[Luke March]

So I decided to give etching a try.

The goal here was to etch a design into a plain piece of steel. The particular piece of steel was a belt-end for a costume my brother is working on. I am using Beeswax as a resist, melted onto the piece of steel; I then use a scribe to scratch in the design.

For the acid I am using Muratic/Hydrochloric acid from Lowe's. (I think it says something around ~30% concentration)

For the first test, I tried the acid diluted, about as much water added as acid. After an hour, nothing appeared to be happening, so I added some Hydrogen peroxide (the diluted stuff in the brown bottle). After about another hour, we removed it from the acid, rinsed it off, and removed the beeswax; the design was visible, but was so shallow it could easily be sanded off.

For the second test, we tried to let the acid be more concentrated, and let it set overnight. In the morning, after several dreams in which strong acids and their corrosive effects figured strongly, I rushed outside to check the progress. I could not really tell much of a difference from the night before. Dissapointed, I let it set out for a couple hours.

A few hours later I came back to do the third test. The lines were all rusted. Some of the wax had flaked off when I sprayed it with the hose to get the acid off, so I took it back to my toaster oven and let the wax re-melt and flow. Then I re-scratched the lines, being sure to actually scratch the steel itself, so I knew the lines were there. For this test, I only used enough water to cover the piece, then added more acid than there was water. I then added peroxide, since that seemed to help before. I had also read that adding table salt (NaCl) to such a mix could speed the process, so I added that until it stopped dissolving.

After four hours in this bath, on a warm day in a black plastic container in full sunlight, this is what I got:



After some cleanup with fine sandpaper:


Now, I am not totally dissatisfied with the result, but I was really looking for a deeper effect, such as can be seen about 2/3 of the way through this video: http://www.wetanz.com/assets/videos/swords/LOTRSwordVideo.mov

So I've been thinking about what I could do differently to get a deeper effect. Obviously I could try to leave it in longer next time, but one of the resources I read indicated that an etching should never be left in longer than four hours.

I also considered that maybe for the particular steel I'm using, a different acid would work better, perhaps Nitric Acid as in the video above, or Ferric Chloride as gets used for etching circuit boards.


So, does anyone have any thoughts on how to get a deeper etching?

[ThomasPowers]

Ferric chloride; fairly safe on flesh compared to the strong mineral acids; but eats almost every metal (save Ti as I recall)

[Woody]

What makes you think that adding hydrogen peroxide to the hydrochloric acid will give you a better etch? You need to think long and hard before mixing chemicals or you may end up with an unpleasant reaction you didn't expect. Here is a procedure that works well for etching using salt water and electricity. Remember that running an electrical current through salt water produces chlorine gas. Not a big concern with the small amount of salt water here but keep your nose up wind.

Salt water etching

The etching requires three things: a little salt water, 6 volts of good D.C current and some way to mask the surface you want to etch.

I get my 6 volts from a power supply I scrounged out of the back of an old computer at work. Typically these supplies provide +/- 12, +/-5 volts and ususally have a sticker saying which color wires are what. They plug nicely into IIOV line current and supply a good quality DC, at least to the 5 volt lines. I found that they only deliver power when one is drawing at least 300 mA or so, so to make sure it was delivering, I put a few power resistors on a couple of the lines so that when I turn it on, it is delivering power.

I got some cheap (10 for @2.59) alligator clip at Radio Shack and rigged up a little armature on a board to hold the negative clip at an adjustable position.
I place the piece on the board and adjust the negative clip so it is just above the area to be etched, and I clip the positive lead to the piece somewhere else, I put a few drops of sayt water on the spot to be etched and then with a q-tip dipped in the saltwater, clip the q-tip in the negative alligator clip so that it is soaked wtith saline and just resting on the etch spot. Turn on the power and let it sit about 5 minutes.

The salt water is just a pinch of salt in half an orange juice cup (2 oz.) I now this sounds-very unscientific but that is what I have tried. Too much salt makes a very rapid etch. Too little and you won't get an etch. You will have to experiment to find out what you like. I have tried several different masks, including waxes of various ilks, nothing professional, but have found that
scotch tape works great. I use a sharp knife to cut out the areas I want to
etch. Make sure the surface to be etched is smooth and clean. Any grease (from your hands or nose) can make the etch uneven. If anyone out there has some good suggestions for etching masks, feel free to chime in. one of these days I will get around to getting the right material for the mask, but for what I am doing, it is not necessary at this time. The cleaner the DC voltage the better. A 6
volt battery would probably be great, if you could get a used motorcycle battery and then just charge it when you need to. Battery chargers themselves work, but leave a much more ragged looking etch. Experiment some and you will get the hang of it. Its clet , quiet, etc. I do ition the kitchen table and no one cares or worries. One of the best things is that because you do not have to dip the whole piece in the etcliant the mask can be very local. About 1/2 inch around the area to be etched works fine. The saline kind of beads up on the mask and makes it easy to contain and work with.

[Luke March]

Thomas,

Thanks for the tip, I'll have to try that sometime. Perhaps it will work better than what I have done so far.

Do you think my shallow etching was the result of the metal being incompatible with the acid? Or should I have left it in longer? Or, perhaps there was something else I failed to do?

Woody,

I learned the H202 + HCl trick when learning to etch my own circuit boards. It was one of the recommended formulas I found when researching the subject; rest assured I did not simply say "hmmm, maybe if I add this chemical." I am aware that combining chemicals together when you don't know their effects is a pretty bad idea (for example, mixing ammonia and bleach can produce vapors causing death.) Just a side note, the peroxide really does help, at least on copper; none of my circuit boards have turned out correctly without it (in an HCl mix).

Thanks for the description of electro etching; I had thought about electro etching, but figured that (at least to begin with) I would do acid etching because I already had the right materials. (Or so I thought, anyway).

[Woody]

Acids react differently with different metals. Usually HCL is pretty agressive to steel, but that can be effected by the alloy of the steel. Heating the acid solution will increase the corrosion rate also. I etch my damascus blades in ferric chloride that I warm up a bit (around 160 F) however if the steel has nickel in it, the ferric chloride won't etch it very well. That is why we use a steel with a nickel alloy in it inconjunction with just a plain carbon steel, the Ferric Chloride attacks the plain carbon steel and leaves the nickel steel virtually untouched so you get a high degree of contrast. You never did say what type of steel you were trying to etch. That will make a bit of difference on what you choose to etch it with.

[Luke March]

That's exactly what is puzzling to me. By all accounts, the etchant was strongly corrosive. I don't know what the exact alloy was; it was part of a 4'x8' sheet of 16g steel I bought from the local steelyard. I didn't think to ask what it was when I bought it, but they only had one type of steel sheet. By the way its finish looks and by the way it work hardens, I would guess it's hot roll - I don't know if that means A36 or some other alloy. It's certainly not stainless.

To test my acid I took another scrap piece of the same material and stirred the acid with it; the surface oxidation was dissolved to show bare metal in under a minute. I also took a bar of layers of this same steel forge welded in a stack with a different steel (sort of a damascus-prototype-test-piece), polished the end, and dipped it in the acid. The layers showed up immediately - though that may have been due more to the other steel.

Bubbles showed up on the workpiece constantly, though I knocked them off occasionally (every 1/2 to 1 hour). They always reformed after just a few minutes though. I'm beginning to wonder if the presence of the bubbles prevented the acid from etching properly.

[Woody]

You got me stumped. Sheet steel from your local supplier should be just plain mild steel. Mild steel is made to a tensile strength specification and the contents of the steel may vary. It is sort of like trying to trace the ancestry of your local alley cat. Give the ferric chloride a try and see what happens. Or perhaps see what acid straight from the bottle does to a small piece. Also is all the wax cleaned off, even minute traces left on the surface could impare the etch.