Thanks for the response.

I am ready to jump into this, using a variety of resists generated with a printer and something like Press-n-Peel. I would use a Ferric Chloride etch.

The thing I can't find on line is anything about how to prep the steel before applying the resist. The metal I want to use comes from a construction steel warehouse. It’s battleship gray. Most people etching are starting with copper, zinc, or steel in rolls which needs minimal cleaning.

Suggestions?

sandblast it. that will get you through the mill scale and te acid would not have to absorb the scale before eating into the steel. or at the very least clean it so there are no oils acting as a resist as well....

As with any metal prior to a process cleaning is advisable, but in the case of steel, which might have some kind of oil or wax residue on it to prevent corrosion, that should be cleaned off prior to applying any kind of etch resist and that based upon the fact that lubricants stop anything that is designed to adhere, sticking. An etch resist that is not adhering well could be the difference between a pleasing result and another item in the scrap bin along with the dissapointment and waste of time and resources.

There are many methods of preparing steel for further processes, but at least one might want to remove suspected grease, wax and oils with a suitable solvent, wood alcohol or similar, for even finger grease can be a problem.

Etch resists I have used include parcel tape, nail varnish, masking tape, bitumin and even indian ink based permanent marker. One has to consider based upon the process at hand what that process might do to the etch resist. With nitric acid bitumin appears to be the best, electro etching; nail varnish works well and ferric chloride on copper, parcel tape did a good job. One can also go the traditional route and use bees wax for a etch resist.

As to mordants for etching, ferric chloride is one, although I have only to date used that rather successfully on copper,( it came in a PCB etch kit), and nitric acid on silver. I have also had much success with a home made electro etch on steel, a process involving nothing more than a 9v battery, a bit of wire, several cotton ear buds and salt water, the cheap way of doing things although one has to watch the by product of the process, CHLORINE GAS, so a well ventilated area and don't work over the process, but the same applies with both nitric acid and ferric chloride, the processing vapours are definately not good for one's health.

So whatever you use, before you use, check out what hazards to health exist and take proper precautions to ensure your and those around you's continued health.

I am sorry, I failed to identify myself in my first response due to failure to log in :-)

My steel pieces are all machined first and then sanded to 400 grit. I find that even small machine marks interfere with the pattern transfer.

I usually clean the surface with acetone to remove as much oily residue as possible and then move to second stage of cleaning with Home Depot Zep Heavy Duty cleaner. With steel this is tricky as you get almost immediate rusting if you are not careful. I do all the rinses with distilled water. With tap water the rust appears almost before you remove it from the rinse.

Do this just before the pattern transfer with Press-n-Peel or resist application else if you leave it for any legth of time you will get rust.

You will get better results with Ferric Chloride if you warm it up: I have my bath (Pyrex dish) on a table top plate which in its past life was meant to keep dinner warm. I usually try to keep the temperature around 35 degrees C.

Depending on how deep you want the etch to be you may have to keep the workpiece in the bath for quite some time (1 hour give or take for 2-3 mils). Many of the resists mentioned will simply dissolve or peel off well before this. For the same reason you need to pay attention to stopping the etching on the reverse side of the plate.

To my knowledge there are no fumes produced by Ferric Chloride etching.

I have done electro-etching with stainless steel cathode in a weak saline solution. There is no chlorine gas produced in this set up but a fair bit of hydrogen which has its own potential risks.

crquack

I would appreciate any troubleshooting suggestions. I'm etching on soft steel. I am using a 3 cm by 10 cm (4 ml thick) piece as a test. I have pickled off the mill scale. I transferred a pattern using photosensitive film. The etchant is the “Edinburgh Etch” ferric chloride and citric acid, recipe from nontoxicprint.com. The tank is a vertical capped piece of PVC with aeration. The temperature is 32 C. I'm getting very little bite even after three hours, even on the bottom unprotected surface.

Edinburgh etch is going to be pretty slow on steel, I would think. I use ferric chloride to etch pattern-welded steel to reveal the pattern, but we're only talking a few microns bite to do that. That takes anywhere from 20 minutes to a couple hours depending on how fresh the FeCl is and the temp. Even with citric acid added I doubt it would be much faster than that, though I've never personally tried the Edinburgh etch.

For a more aggressive etch on steel I think most people use nitric acid. Metallographers use Nital, a mixture of nitric acid and alcohol, to reveal grain structure and they are generally using a very dilute solution like 2% or something.

If you plan to use Nital or any acid/alcohol mixture you need to know exactly what you are doing or you can form compounds that are highly unstable - think explosive.

The only steel etching I've done other than using FeCl on damascus steel was with a dilute nitric acid solution in water. It has been decades since I did that so I have no recollection of what strength I used.

I would suggest you check with your local college chemistry department (or metallurgy department if they have one) to see if they can offer some guidance. All etching compounds have some greater or lesser degree of danger involved with their use - you need professional guidance.

I cannot fault you on your set up.

I have used both straight FeCl3 and Edinburgh Etch on steel. Neither is great. In fact I have all but abandoned etching steel with FeCl3. As you noticed even after 2 hours you get less than 0.001" depth. If there is any cleaning to be done afterwards you almost certainly remove the etching as well. This is no good.

I am reluctant to use noxious substances such as strong acids but that is just me and my circumstances.

I have made quite a bit of progress using electro-etching. It is a whole different animal and has its foibles. However, when done right the depth of etch is marvelous after only 15-20 minutes. The main hazard is production of hydrogen gas. According to my calculations for a piece of your size the total volume is quite small.

Here is an early example:

http://www.flickr.com/photos/27683124@N07/5317810623/in/set-72157605638700703

If you want to get into it let me know.

crquack

Thanks crquack. I'd appreciate it if you could point me in the right direction on the web or give me a few notes that would make it possible to cut quick to the chase.

Three feet is about the longest piece of steel I want to etch
Hopefully I can example of steel I want to etchattach an image of metal I want to work with, etching it before it's bent of course.

I was under the impression that electro etching would work for small pieces like stamping a tool, but that I might not be able to use it for larger stuff.

Crquack,

I'd like to hear how you do the electro etching myself. I've done okay in the past using nitric acid, but I can't get it down here without paying through the nose for Haz-Mat shipping. I have what I need to build a power supply for electro-etching so that would be a dandy way for me to go.

I know that one of the issues with any electrolytic process is anode/cathode density and distance - I've dealt with that on electrolytic de-rusting and figured out ways to get what I need on some irregular shapes. I suppose the same thing will apply on the etching?

OK, I just PMd Mark with some links but you have already gone one step further.

This is my most recent set up:

1) Regulated power supply 30V/3A - new about $150, mine was $6 in a garage sale so I should not be too smug. My experience on pieces up to 5.5" diameter has been that I have no difficulty getting up to 2A with low voltages. So car battery with a rheostat or something similar would do.

2) Electrolyte - "weak" NaCl solution (1 teaspoon per litre) with half a cup of white vinegar. I know I sound like a cook but what I am stressing is that accurate quantities do not seem essential. The vinegar is important because the by-product is a horrible green/orange precipitate of ferric and ferrous hydroxide if you don't use it. As far as I can tell with vinegar the iron stays in the solution as a ferrous acetate

3) Stainless steel cathode. I etch flat pieces so the cathode is flat. To get an even etch you want the electrodes equidistant over the whole etching area otherwise the current density will vary as will the etch depth. If you etch steel balls or something like that you may have to adapt the cathode.

4) Recently I have discovered a phenomenon which is somewhat controversial but I chose to believe it as true because it behaves consistently with my theoretical explanation: The hydrogen bubbles cause cavitation damage to the resist and consequently foul biting. It took me several different set ups to come to that conclusion. I was always running the set up with the anode on top, suspended in the electrolyte and the cathode on the bottom. The hydrogen bubbles passed by the anode and many of them collapsed there. When I reversed the position and made a new stainless steel cathode (perforated to let the bubbles out) there was a marked improvement in the qualty of etching. However, I have several more of these lined up to confim that this is indeed the case. That there is significant energy stored in these bubbles was demonstrated by their collapse on the surface which causes little geysers up to 2 in high and the noise when some of them burst under the cathode.

5) For resist I use Duplicolor black primer, four coats. They go on fairly quickly with hair dryer in between. After I scratched the pattern into it I have taken to baking it for 35 min at 300F. It might make it more resistant - I cannot confirm this without doing a double blind study :-)
I will be using Press-n-Peel again but right now all the pieces are manual.

I think that's about it in a nutshell. Let me know if there are questions.

crquack

http://www.nontoxicprint.com/electroetching.htm

The above link is where I started. It outlines the basics and has some decent pictures. Title: "electro etching made easy."

It recommends (for steel) an electrolyte solution of 200 g ferrous sulfate to one liter of water, so reading on electrolyte recipes is in order.

I'm off to find a power supply and will keep you posted.

I'm trying to etch a pattern on a strip of metal about the dimensions of a thin yard stick, or 25 inches of a yardstick. Transferring the pattern using a photo sensitive film has worked smoothly.

I've just started reading about electro etching and haven't tried it, so asking questions at this point seems a bit lazy, but one question I is have is about the position of the electrodes. The PVC I set up to etch chemically, barely contains the steel. The steel width is 3 cm. The diameter of the PVC is 4 cm. It only takes 1.5 liters of etchant to surround and cover the steel.

I gather by crquack's #4 paragraph that his anode and cathode are lined up horizontally. I'm planning on lining up mine vertically at this point, and have yet to get a clue as to how far apart they will have to be which determines how big the diameter of the PVC will be which determines how many liters of electrolyte I will need.

Thanks for any comments

That's great, thanks! That gives me a starting point and some valuable insights about the binding of the iron in the solution. Now I have to make the time to try a few experiments and see what I can do with it. I have two old Dc arc welders that should supply about all the current I woud need to etch Volkswagen. (grin) Probably need to use a current limiting resistor or two. Or just drop a light bulb in series as I do with other things - us poor folks gots poor ways!

Given that I have a 55 gallon stainless steel drum sitting around doing nothing and those welders for power, I'm thinking that the drum would make a dual-purpose cathode and reservoir. The distance from the work to the wall of the drum is greater, but the available power is pretty great so maintaining sufficient current density shouldn't be a problem.

Have you ever tried periodic current-reversal to ensure a smooth etch? Back when I did some plating and electro-forming, I would do this to get a more even deposition. I'm wondering if this might help to get a smoother etch by dislodging bubbles as they first form, rather than waiting until they get big enough to break loose and take some of the resist with it. Any thoughts on that?

Rich

I have not tried that. I have only recently identified the hydrogen bubbles as a source of a problem. I just could not understand or believe that bubbles forming on the *cathode* would cause a problem on the *anode*. I read a lot about cavitation before I sort of convinced myself that that was the nature of the problem.

Stainless steel drum sounds interesting. You will have to visualize the current paths. There will be a tendency for the current to "get around the back". With the flat electrodes I find that there is remarkably little effect on the reverse side of the piece but occasionally there is a surprise. I was using a rare earth magnet to hold a connective strip of thin brass to the back of the piece (in those days the anode was on top). When the electrolyte with salt only and no vinegar foamed so much (due to the FeOH precipitate) that it brought the electrolyte layer over the top of the anode. It reached the magnet and started chewing it up with a strange black deposit forming on the cathode. I haven't got a clue about the chemistry involved.

Anyway, Mark, I read and answered your e-mail before I read this thread, so some of the questions have been answered.

It is a nice link you posted. I have them bookmarked for the Bordeaux etch and have not been there a while. I see this comprehensive treatise has been added in 2010.

Just beware: He seems to work mainly with copper. A different beast altogether.

Another thing: he makes a big issue out voltage applied to his setup and then compares the results achieved with different concentrations of electrolyte. This I think is an error. The important variable you want to know is the *current*. I contend that he would have achieved all the different etches if he kept the electrolyte constant and varied the current. If you keep the voltage constant and vary the concentration of the electrolyte the current will also vary.

I think it is helpful to measure both, the voltage and the current but of the two the current is more important. That is what does the work.

crquack

I'm etching the first strips today. They are 12 inches long, 1.5 inches wide, and about an eighth of an inch thick. To get to 2 amps, I have to use 10 volts. Is this reasonable?
Some sites dealing with copper are etching at 1 volt and warning about hydrogen build up at higher voltages.

craquack, when you are getting two amps, what voltage are you using? From your photos on Flickr, it seems your sundials contain approximately the same metal I am testing.

Two hours later. First etch was good. Using repositional glue, I stuck a stencil on steel, then sprayed the exposed steel with positiv 20 (photo sentive spray) It developed and turned navy blue and hardened. Etch was deep.

Second try is not working. Same size metal, same resist, but the power source is overloading. If I put the two plates in an inch or two of electrolyte, instant action on the anode and cathode... 20 v, 2 amps. But back in the vertical tank, overload.

Mark,

The current density is a factor of distance between cathode and anode, electrical potential of electrolyte, surface area of anode and cathode, temperature, etc. If the distance between the anode and cathode are the same in both situations, and the exposed area of metal the same, then the next thing is probably the potential of the electrolyte itself. Is this the same electrolyte you already used once? If so, it may have dissolved metal suspended in it that is increasing its electrical potential. That's my best guess, anyway. Hopefully, crquack will have additional/better guidance to offer.

Rich

What Rick said. And given that 10V is not unreasonable. My plates tend to be closer than yours so I was running around 5V.

Questions:

1) Is it the same pattern you are doing second time round?
2) Is it the same electrolyte? If so what are you using?
3) If you are using mild steel for both electrodes I cannot vouch for the cathode behaviour with ongoing use, i.e are there any surface changes?
4) Any chance you are getting accidental shorts in (or outside of) the tank? What happens if you reduce the voltage?
5) I am still puzzled about your pattern transfer: Your pattern is on a stencil, then you spray over the stencil with the photosensitive paint which is allowed to harden in the sun. Why? Would not ordinary paint do? Like I am using here in a process which is essentially a "reverse stencil":

http://www.flickr.com/photos/27683124@N07/4189322282/in/set-72157605638700703/

How do you get the pattern on the stencil? Manually? Computer?

Finally, I do not recall hydrogen problem with copper cathode, brass anode and copper sulphate (acidified) electrolyte. It should be straight copper in off the anode and deposited on the cathode. However, I haven't done any brass that way recently.

Keep us posted, this is interesting.

crquack

Yes it was same electrolyte, 1 t. salt, ½ c. vinegar, 1 liter water. I just assumed the electrolyte could be used for several etchings. Possibly, I was led astray by this clip?...

http://www.youtube.com/watch?v=xl-IG5zNVeM&feature=related

The pattern was the same.

With the voltage reduced all the way, it was still overloaded which immediately made me think there was a short, but placing the the anode and cathode in a very shallow bath always got things going, no overload.

I was intending to use a photosensitive film, but I am confused about how to pull this steel out of a vinegar bath, dry it off, and get the film on before the metal is covered with rust.

I decided to dry the metal off, slap on the stencil, and spray resist. I used the resist instead of paint thinking it would dry faster and be harder.

Today...same electrolyte recipe (new batch), same size steel, same pattern, but I switched to spray paint. I got immediate overload until I moved the cathode and anode about five inches or 12-13 cm apart. With voltage turned down all the way, the readings were amps = 2.5, volts = 15– 20. I etched for about an hour. The power supply overloaded twice. I switched it off, waited half a minute and switched it back on. It ran for 20 minutes again at the same voltage and amperage.

I only let the paint dry an hour, two coats. Obviously the surface under the resist is pitted, but I can work on better resists later.
mark
To boil it down:

1.) I'm surprised the anode and cathode had to be so far apart and am thinking of less salt in the electrolyte.
2.) How am I going to get a film on a steel plate when it is rusting before my eyes?

Marketched and cleanedresist

Mark,

As I think I mentioned in an earlier post, the electrical potential of the electrolyte is one factor in current density and the distance between anode and cathode is another. Those two factors are 75%of the issue, with surface area being the next biggest factor. Since the surface area didn't change, that factor can be ignored for now.

As for the strength, or electrical potential, of the electrolyte, the salt has the main effect on that. Cutting the salt by half should show a significant change in the current density. I'd start with that. If it seems a bit slow you can decrease the distance between electrodes.

I would suggest that after you pull the steel from the acid (vinegar), you then drop it in a solution of bicarbonate of soda (baking soda) and water and swish it around for a half minute. That neutralizes the acid. Follow that by a rinse in fresh water, preferably either distilled water or rainwater, but deionized (purified) water will work okay. When you take it out of the water, immediately force dry it with a heat gun or hair dryer.

You can, if you have it, rinse it with acetone after the water - acetone is miscible with water in any concentration and it is extremely volatile so it takes away any traces of water. I've found, however, that simply neutralizing the acid then rinsing and force drying works fine and you should then have plenty of open time to apply the resist. You will also have a surface that is prepped to receive the resist so it adheres much better. I use a 10% solution of hydrochloric acid in water, rather than the vinegar, because it removes mill scale quicker and etches the surface of the steel a bit more, giving a better "tooth" for paint or resist.

OK, a few points:
1) The area to be etched is quite large, at least compared to what I do. With high voltage high current is to be expected.
2) You are using 15-20 Volts. That is clearly too high. Reduce it. Down to 1V if necessary.
3) What are you doing about the back of the plate? Is it covered with resist? Did you get any etching there? I.e. does it contribute to the current drain?
4)You say the area under the resist is pitted. This is not obvious from the pictures (I think they are opposite orientation but one can work out which is the etched and which is the covered area I think). Does that mean that you removed the pitting by cleaning/abrasion? If ther *is* significant pitting that means that the current is getting through the resist and the effective etched area is larger than you think - hence the higher current.
5) The clip you linked is a fine example of what happens if you do not add vinegar to the electrolyte. The gunk is not iron oxide, it is iron hydroxide. Vinegar neutralizes it.
6) By all means make the electrolyte more dilute. This will increase the effective resistance and lower the current. However, it seems to me that you need to work on the voltage regulation. Do you mean that your power source overloads if you run it higher than 2.5A? Maybe cosider a different power source - a car battery should do the job, but you still need to be able to adjust the voltage.
7) The surface prep prior to resist. I am not sure where the vinegar comes in. I tend to do a good mechanical clean with abrasives (oddly enough even just an 80 grit was OK with the Duplicolor primer, however, avoid leaving any machine marks, even a slight trace caused foul biting). Then I clean with acetone and spray with resist. I found that this works both with Ferric Chloride and electro-etching. I have never felt the need to get the steel clean enough to pass the water-break test (in which case it starts rusting very very quickly).
8) I do not share the enthusiasm of the metal arts community for acetone as a desiccant agent, at least not in the manner it is often used (e.g. just spraying it on and allowing it to evaporate as if it magically pulled water with it). However, wiping the abraded surface with it vigorously removes any residual garbage left over from the abrasion and probably does remove whatever moisture there was. There is, however, another issue: The commercially available acetone has some oily impurities in it which stay on the surface (if you do not believe it try the waterbreak test after you have wiped the surface with acetone). This does not seem to matter in this application though, but can screw up patinas and certainly electroplating.
9) Just as an afterthought: 20V x 2.5 amps is 50W. This could cause appreciable heating in the bath. Does any part of your circuit get hot? Does the electrolyte?

Keep it up, I am fascinated.

crquack

Okay, this is starting to blow my mind which is good.

Amps (Current) = Volts (Potential) divided by Ohms (Resistance).

Resistance is increased by reducing the salt in the electrolyte. (Or by moving the plates further apart, forget about that for now.)

2.5 Ohms = 20 Volts / electrolyte resistance.

When I cut the salt in half and then in half again, doubling the resistance, the voltage stayed the same. Amperage fell.

This makes perfect sense, but it leads to the question of how to lower the voltage if the voltage is already regulated as low as it can go.

(Your suggestion is noted: “Try another power source.”)

Shooting in the dark, I sprayed resist on the back of the plate being etched…no change in Amps or Volts.

I reduced the size of the cathode plate by half…no change.

Then I switched to a new tank which allowed the plates to be further apart.

I am getting 2.5 amps with the plates about 30 cm apart,voltage slightly lower 13 or so, but these are test plates and are about 1/3 the surface of what I’m hoping to eventually etch.

This makes me imagine a tank three of four feet long.

I’m going to make some different leads from the + and -, using a lower gauge wire.

Last, why is 15 volts too high?

Many thanks for this tutorial.

Higher voltage means higher electromotive force (EMF). That means you get a "faster" bite, which is not always good by any means.

Crquack is right about the acetone - if you're going to use it you have to get the "reagent grade" not the stuff they sell at the hardware store. As he noted, that shouldn't matter in this case. For the record, I agree with him on the use of it as a dessicant rinse - you're mostly wasting acetone doing that if there is appreciable water to be removed. That's why I recommend the heat gun.

1) "2.5 Ohms = 20 Volts / electrolyte resistance."

No. Did you mean 2.5 *Amps* ?

2) "When I cut the salt in half and then in half again, doubling the resistance, the voltage stayed the same. Amperage fell. "

As would be expected.

3) "This makes perfect sense, but it leads to the question of how to lower the voltage if the voltage is already regulated as low as it can go."

Why? What is stopping you from putting a resistor/ lightbulb/another electrolyte tank/graphite pencil in the circuit in series with the etching tank? A resistor of a value equal to the resistance of your etching tank will drop the voltage across the tank by half. It will of course also drop the current in the circuit by half.

4) "Shooting in the dark, I sprayed resist on the back of the plate being etched…no change in Amps or Volts."

OK, so not much current going off the back of the plate. That tends to be my experience too. It takes "the path of least resistance" :-)

5) "I am getting 2.5 amps with the plates about 30 cm apart,voltage slightly lower 13 or so, but these are test plates and are about 1/3 the surface of what I’m hoping to eventually etch.

This makes me imagine a tank three of four feet long."

Again, you need to drop the voltage.

6) "I’m going to make some different leads from the + and -, using a lower gauge wire."

What you will be doing is essentially what I suggested in (3) but rather ineffectively and in an uncontrolled fashion. Your wires will get warm.

7) "Last, why is 15 volts too high?"

It' s too high only because your power source cannot cope with the current generated by it through the low resistance of your etching tank. Note the guy in the video link you posted was running his set up at *10 Amps*.

---------------

My power source is a luxury, the predecessor of this:

http://www.bkprecision.com/products/model/1730A/analog-dc-power-supply-0-30v-0-3a.html

I can set the current and keep it constant at whatever level I choose up to 3A. Today I did a plate slightly smaller than yours but with less metal exposed. I had the electrodes about 15 mm apart, the same electrolyte. I run it at 2 Amps for half an hour. Because of this thread I took particular note of the voltage: I started at 8V and, interestingly, as the process progressed over half an hour the voltage dropped to 6V. The electrolyte resistance must, therefore, be dropping as a result of the process. Presumably something to do with continuously adding Fe++ ions which stay in solution and do not precipitate out (although at the end the electrolyte was beginning to show a brown tinge suggesting that the acetate was used up.

Given the large area of exposed metal in your case and a comparable electrolyte I would expect the necessary voltage to be even lower.

crquack

"2.5 Ohms = 20 Volts / electrolyte resistance."

Yes, scratch out ohms, replace with amps.

A variable resistor wired in series worked just fine, but I'm surprised I had to do this. The voltage knob on the power source is another variable resistor, and I would have thought doing what I'm doing, I could have used it to reduce the voltage to at least 5 volts.

But what do I know? A little bit more than yesterday.

ive loaded two pics for you to see the result

Nice results, though the process to obtain them sounds a bit exciting, to say the least.

1) I am not seeing the pictures.
2) Try aluminum with Ferric Chloride. Similar excitement on a smaller scale. Interesting result, too:

http://www.flickr.com/photos/27683124@N07/5225357650/in/set-72157622484352534

crquack

the photos are uploaded to recent images