[Mark Proulx]

I’m trying to cut and macro etch some MIG-welded carbon steel T-joints to assess penetration. I have watched numerous videos on this subject on the “Welding Tips and Tricks” channel and have tried to replicate the process using Naval Jelly as an etchant. For the life of me, I can’t get results that look anything like those shown in the videos. The weld beads darken as expected, but the base metal pieces tend to remain shiny and impervious to attack by the etchant. Heating the piece helps a bit, but doesn’t come close to giving me the results I’m looking for.

Any suggestions as to how I can improve this would be greatly appreciated.

[LtBadd]

Hey Mark. let us know your procedure
you cut, grind, then finish with a polish? The higher the polish the better the etch
How long do you leave the solution on the test piece?

[Mark Proulx]

Sorry for the tardy reply. I wanted to include photos, so I had to wait to get out to the shop. The uploaded photos show what I’ve been doing. (I know that one of the beads exhibits porosity; no need to flag that.)

I’ve tried letting the jelly sit overnight; this didn’t help. I have tried heating the sample with a propane torch; this helps darken the beads but has little effect on the base pieces themselves.

When the jelly has had a chance to work, I’ll post the result.

Update at 1708 PDT. This etch worked much better than previous attempts, but it is still evident that the base pieces were still much more resistant to attack than the welds. Note the shiny spot on the leg - not etched at all. In previous specimens, this shiny finish was virtually everywhere on the T pieces. Weird.

[Oscar]

IMO, you went too far with the paste polish. I would have stopped at 120grit/ red abrasive pad.

It's pretty easy. Using naval jelly:

[LtBadd]

Oscar not sure why your pics on this forum are sometimes truncated. Maybe too high of resolution.

[tweake]

Oscar not sure why your pics on this forum are sometimes truncated. Maybe too high of resolution.

its the forum limiting the display size. open the pic in a new tab and you will get the full pic.

[LtBadd]

Yes that works, but it is the resolution

[Oscar]

Yes this forum sucks for pics, I'm done with having two copies of my pics (one regular, and one small for this forum). A lot of other forums automatically resize. From this day forward, everybody must open my pics in a separate tab!

[BillE.Dee]

Oscar, the navy jelly works on steel, what do you use on aluminum? I've tried all kinds of wheel cleaners and oven cleaner from wally world...fail.

[Oscar]

I've actually never tried to etch aluminum, but why wouldn't the oven cleaners work? I mean, it's been shown in videos.

[BillE.Dee]

don't know Oscar. I've tried al wheel brighteners and maybe the oven cleaner from wallyworld has something missing or different than E Z off brand. OR, more than likely I'm not patient enough for the stuff to work.

[weldin mike 27]

Jody uses draino on aluminium.

[Mark Proulx]

@Oscar:

Big time thanks for the suggestion. I backed off on the shine and obtained a much better result.

[Oscar]

There ya go. What was the last grit/surface prep that you settled on before you etched?

[Mark Proulx]

Here’s another. Same parameters:

[weldin mike 27]

Funny, I read that the shinier the better. Maybe that was for professional strength etchants.

[Coldman]

Maybe the polishing paste left a wax coating.

[Mark Proulx]

@weldin mike 27:

That’s what I thought, too. I suspect that you’re correct regarding the use of “real” etchants.

[Mark Proulx]

@Coldman:

I thought so too. That’s why I wiped the surface with isopropyl alcohol after polishing. It did not seem to matter.

[Arno]

Funny, I read that the shinier the better. Maybe that was for professional strength etchants.

Quite likely. By polishing it to a high shine you are reducing the total surface area of the base material to (close to) it's bare minimum.

To get an acid to etch a surface like that well it needs to be high strength (or more agressive type) to work on/into the smaller surface or you will need to leave it much longer and refresh the acid often.

A somewhat more coarse surface exposes a lot more base material to the acid so a less agressive one will be able to work on the surface faster and show results/discolorations. (a bit like rust starting slow on polished steel but accelerating rapidly once it manages to start some pitting..)

A high polish and etch should be able to show up smaller (grain) differences in the metal though (and then under a magnifier/microscope), but probably be overkill for an individual just wanting to check some of his welds and not some metallurgic lab..

Bye, Arno.

[weldin mike 27]

Thanks Arno. Yep, the difference being the controlled stuff that scientists and professionals use compared to home gamer stuff that happens to etch.