Metal etchant acting weird

[MillenniumFalsehood]

So I bought some ferric chloride on eBay thinking it was a solution. But when I got it in the mail, it turned out to be the powdered form. Luckily all you need to do is mix it in warm water, so I did that. But it turned out I used too much water and so the solution was weaker than I needed. No problem, I'll just leave the metal in the basin longer.

Well, now it's green with a brown film on it. What gives? What did I do wrong?

[jpolacchi]

I think it is AK that has a metal etching prep made "just for" photo etch brass and I suppose other metal parts if it worked on them too?

[MillenniumFalsehood]

I already have a bottle of PCB etchant on its way here, I just wanted to know what could have caused the reaction I got. It's so weird.

[seam-filler]

Ferric chloride solution can turn green when contaminated with phenols. A lot of anti-bacterial cleaners and washes contain phenols so it looks like you've got a bit of contamination from cleaning. The brownish film is likely to be contamination from fats or fatty acids (also sometimes used in cleaning solutions).

Such contamination is unlikely to affect the etching capabilities of the solution.

[starseeker]

I don't know exactly what you're describing there, but if you're saying that you're leaving the metal for a longer time in a weaker solution, you don't want to do that. When I etch, the weaker the solution gets, the longer it takes to etch through, and the resulting etch itself isn't of the crispest quality.

Starting with fresh ferric chlorite (you should be able to get the solutions at any large electronics supplier, if you have any locally), the etching goes quickly and you can get some very fine results indeed. But the more you use the solution, the longer it takes, and the fineness you can achieve starts to drop off quickly as the solution becomes more and more saturated with brass. FeCl works best and fastest when its hot, so a good heater (NOT an aquarium heater, no matter what David Merriman recommends - they don't get hot enough, they're more fragile and eventually get eaten, too. Get one from the electronics supplier while you're shopping. And a pump to circulate the solution is a necessity, too). Draft your etch so that you have the smallest possible amount of brass that isn't a part being etched. All that excess dissolved brass will do it dilute your solution needlessly.

A four liter container of solution will etch about six 8x10" sheets of brass before you notice the change. It'll do maybe 4 or 6 more before it's really not worth using anymore. The first sheets to come out of the bath will be beautiful and shiny, just like aftermarket. By the fourth sheet, they're looking slightly tarnished or brown and the solution is getting opaque. And at the end of the solutions potency, they take much longer to etch and they come out looking really brown and grungy, indeed. They can be polished with fine steel wool or wet and dry, but you have to weigh that against the risk of damaging the parts.

Here in Canada, MG Chemicals sells everything you need from chemicals to equipment to sets. There has to be good sources for this stuff somewhere near you, too.

And standard Norm Abrams type preface: don't even think about etching indoors, or even in an enclosed space like a garage with the doors open. The fumes will lightly etch everything in the garage, from hanging hand tools to table saw tables to cars, and especially any ventilation hood you might think of using. And eye and lung protection is absolutely essential. I end up dressing myself in what must look like a peasant's version of a hazmat suit. Very colourful for the neighbours, I'm sure.

[MillenniumFalsehood]

I don't know exactly what you're describing there, but if you're saying that you're leaving the metal for a longer time in a weaker solution, you don't want to do that. When I etch, the weaker the solution gets, the longer it takes to etch through, and the resulting etch itself isn't of the crispest quality.

Starting with fresh ferric chlorite (you should be able to get the solutions at any large electronics supplier, if you have any locally), the etching goes quickly and you can get some very fine results indeed. But the more you use the solution, the longer it takes, and the fineness you can achieve starts to drop off quickly as the solution becomes more and more saturated with brass. FeCl works best and fastest when its hot, so a good heater (NOT an aquarium heater, no matter what David Merriman recommends - they don't get hot enough, they're more fragile and eventually get eaten, too. Get one from the electronics supplier while you're shopping. And a pump to circulate the solution is a necessity, too). Draft your etch so that you have the smallest possible amount of brass that isn't a part being etched. All that excess dissolved brass will do it dilute your solution needlessly.

A four liter container of solution will etch about six 8x10" sheets of brass before you notice the change. It'll do maybe 4 or 6 more before it's really not worth using anymore. The first sheets to come out of the bath will be beautiful and shiny, just like aftermarket. By the fourth sheet, they're looking slightly tarnished or brown and the solution is getting opaque. And at the end of the solutions potency, they take much longer to etch and they come out looking really brown and grungy, indeed. They can be polished with fine steel wool or wet and dry, but you have to weigh that against the risk of damaging the parts.

Here in Canada, MG Chemicals sells everything you need from chemicals to equipment to sets. There has to be good sources for this stuff somewhere near you, too.

And standard Norm Abrams type preface: don't even think about etching indoors, or even in an enclosed space like a garage with the doors open. The fumes will lightly etch everything in the garage, from hanging hand tools to table saw tables to cars, and especially any ventilation hood you might think of using. And eye and lung protection is absolutely essential. I end up dressing myself in what must look like a peasant's version of a hazmat suit. Very colourful for the neighbours, I'm sure.

Oh god, thank you so much! This answers so many questions!

I'll be using FeCl in the future, but the next set of parts I make will be etched with a solution of NaOH and H2O2. It was demonstrated on Plasmo and it seemed much quicker so I think it would work better on the 0.010" sheet I was etching.

Another couple questions I had were in regard to the parts that were successfully etched. First, they ended up with a coppery finish on the etched side. Should I take this to mean that the FeCl leeched the zinc from the brass, leaving a copper matrix? Second, the parts seemed to want to curl up, and this made them etch unevenly, with the outer edges etching faster than the center. What could I do to prevent this from happening (I'm guessing using smaller sheets?)?

[starseeker]

You've got me stumped on the coppery finish on the etched side. Both sides of my etch looks pretty much the same, anything ranging from brilliant brass to blackish tarnish. Ah! - I'm going to guess that it's because one side was close to the side or bottom of the etching container. The two sides of the sheet are getting different circulation of etchant. ?? I drill a hole in the sheet I'm going to etch and suspend it via thick insulated Solid Core wire wrapped around a stick that holds it in the etch bath. That allows free circulation on all sides. The closer the part is to the pump's bubbles, the faster and cleaner the part will etch. My larger (+6") pieces of etch will always curl somewhat. Check the wires periodically. The insulation protects them from the etchant. For a while.

I can't remember ever etching anything as thick as .010. I've tried various KS sheets, and the one I like best is .006. Thicker seems to take exponentially longer. I also use Lee Valley's roll of .003 brass shim, tho' the parts will be very thin and fragile. Remember, the smallest through cut you can do is the thickness of the brass you're using. The thinnest partial etch you can do is half the thickness of the stock. An .010 sheet will allow you a through cut of .010" and a line half way through of .005"wide, at minimum. That's if everything works properly, from the etchant freshness to how long it takes, which is helped by hot, circulating acid.

The more sheets you do, you start to lose the fineness as the solution dilutes. So do the parts with the finest etch first. Larger sheets seem to take longer to finish. Probably less concentrated circulation. I like to cut large sheets into smaller ones no more than 4 or 6" square. It may be just an illusion that they seem to etch faster, but on the plus side, if something goes wrong, you only lose a small piece of work, rather than a whole sheet. And on the smallest parts, make extras. It never fails that I forget to attach some of the finest parts to the surrounding sheet in my artwork, and end up with them floating free and dissolving in the etchant, adding needless dilution as a bonus. With big parts, it's easy to add a lot of attachment points. With little ones, there might be just two, and it's easy to miss two here and there. I almost always have to do an extra sheet with every batch to replace lost or over etched or half etched bits.

It doesn't take much to over-etch as the solution dilutes and you end up waiting longer and longer for it to finish. Neutralize the etchant on the part quickly when the part is done. And thoroughly. The neutralizing solution will dilute, too, and it's very disappointing to come back to something that's half gone in the morning that was perfect the previous afternoon.

Stay safe out there! In general, and with etching in particular. Good luck!!

[starseeker]

A couple of photos, mostly old from an old Photobucket album I'd made about etching. This is what my artwork looks like:
https://imgur.com/0ZyTTdp
I always do two sided artwork, which is why I want the parts to etch evenly from both sides. To register the parts, I drill as small holes as I can from register points on one side of the artwork through the brass, and match them to register holes on the artwork for the other side. You can match the sides awfully closely. I always put some lettering (usually just initials and a date) mirror imaged on one side so I always know which side is the front (detailed, hence mirror imaged) side of what I'm drawing.

My etch setup:
https://imgur.com/VH6FWCs
As you can tell by the color, this ferric chloride has been used well. Hidden in there is the pump, and of course that's the heater poking out of the top of the Rubbermaid container. Small footprint and tall container works best for thorough circulation. Have to admit, you can lose considerable weight, etching, mostly via sweat (ie: fear). The "clear" tubing comes up from the aerator pump and feed the aerator at the bottom of the tank.

Checking the progress of a sheet:
https://imgur.com/Ak4oiJj
This one is not quite done. There's the insulated wire that suspends it in the acid bath. Other end is tied to a stick bridging the top of the bath. I do several pieces at a time in the bath, switching their positions as I check them, to try to give them even exposure to the bubbles, which are stronger at the side near the air source.

Finished 1/48 X-15 controls, held up to the sky, to show what fine details you can capture:
https://imgur.com/cNDVAZK

More finished parts, in need of a careful scouring, from the artwork above:
https://imgur.com/quUYIls

And at least 6 month's worth of drafting over the last winter, followed by the anti-climax of an afternoon in the driveway. After spending all that time researching and drafting, to switch gears and suddenly have it all finished so quickly... you've spent so much time getting ready, it's kind of a let-down. At least for me. I really love the researching and drafting part. But:
https://imgur.com/LWRPXg2
Because I cram the parts so tightly together to avoid wasting brass, if I'm doing different subjects, they often end up mixed together, or even surround each other. So these are most of this year's batch, cut apart and sorted.
The 3 sheets of paper at the bottom are 8"x10", to give you some idea of scale. This years batch of etching included, from the top: a lot of Trek, some 1/350 Seaview and FS bits, UNCLE car details (including 1/24 UNCLE guns to push the limits and see just how finely I could etch), some aircraft, spacecraft, X plane, and space shuttle details details, and ribs for a scratch built Aliens Dropship hangar for the Halcyon kit. Parts for 18 different subjects, some for multiples like the shuttles, so for 38 different builds in total. Probably take me 4 years to get all of this put together, given my modelling backlog and the speed at which I build.

Etch's biggest limitation is its thinness. To get around that, you can build up layers of etch. The 1/24th UNCLE gun was drafted to be 4 layers of etch in total. The core two layers are the silhouette of the completely assembled gun, sandwiched by details like the grips and the off-centre scope. Layering is your friend.

How many hundreds of hours of work, all that? Never again. He says. Well, at least for a while...

[MillenniumFalsehood]

I going to copy all that down into a Word document! That's brilliant!

[MillenniumFalsehood]

*snip*
How many hundreds of hours of work, all that? Never again. He says. Well, at least for a while...

Had a question pop into my mind. I was wondering what method you use to transfer the pattern to the brass? I've been using PCB etching paper, the kind that you print the pattern on with a laser printer and then pass over the brass with a laminator. I'd like a better, more home-friendly solution (I have to outsource the printing because I don't own a laser printer and the laminator is in another castle, Mario).