Oxidation on front assembly / retraction stopper

[shutterbug]

Hello!

Today I received a Zeiss GF Planachromat 12,5x 0.25 with really nice optics.
It was very dirty and I knew the front assembly has some noticeably oxidation - the dirt came of quite well but the oxidation remains:



Is there anything I can do to remove that layer of oxidation? I've tried isopropyl alcohol and ethanol, firefighter fluid, so far no success.

[apochronaut]

The alloys in those front bezels are usually unknown but are designed to be corrosion resistant. They have been variously alloys with anything from iridium through gold to nickel. The nickel alloys obviously weren't great but they were never intended to get wet with anything but did. One front bezel on a very old 19th century objective appears to be pure rhodium or possibly iridium. There was no use for those metals at the time and chrome plating had not been invented.
Modern ones on cheaper objectives are more likely plated. Titanium nitride, which is actually a ceramic is a good candidate, so the corrosion may be coming from the substrate. The titanium nitride is very thin, similar in thickness to chromium plating. It is applied in a similar fashion to that of lens coatings.
Be careful using ethanol around lens coatings. It can damage some of them.
If you feel you must brighten that up, carefully plug the lens port and lightly buff it with a fine abrasive paste.

[shutterbug]

Thank you for your advice!
I was hoping there would be some miracle magic solution but it's probably best to either leave it alone in that case. No reason to endanger that lens (unless it becomes a visible problem later down the road).

As for ethanol - so far it's always worked really well with modern and old coatings or just about every type of optical device. It's acetone that I never use because that one can really do a number on your coatings.

[apochronaut]

I once had ethanol damage a costing that was on an objective made in Germany.

[shutterbug]

Are you sure that was ethanol (ethyl alcohol)? not methanol or isopropyl alcohol or denatured alcohol?
Most (if not all) dedicated optical cleaning solutions use ethanol, even Olympus Hyperclean 3310 (which is for cleaning microscope lenses) mainly consists of ethyl alcohol:

http://file.yizimg.com/2700/2012060515452948.pdf

I would strongly suspect that the coatings you had issues with were already damaged and would have shown degradation even when using non-volatile cleaning solutions.

[apochronaut]

Anhydrous Ethyl Alcohol. U.S.P. + 432526. and yes, the coatings may have been imperfectly deposited but who would suspect that at the outset. Previously I.P.A. was probably the strongest solvent I had used on them with no effect. Ethanol speckled them immediately. Henceforward I use nothing stronger in a pure form than N-Heptane to clean microscope stuff. I used to consider ethanol safe and in a diluted state in most cases may be but I prefer not to risk it anymore. It also will dissolve balsam, where IPA won't, so I use it sparingly.

[shutterbug]

Anhydrous Ethyl Alcohol. U.S.P. + 432526. and yes, the coatings may have been imperfectly deposited but who would suspect that at the outset. Previously I.P.A. was probably the strongest solvent I had used on them with no effect. Ethanol speckled them immediately. Henceforward I use nothing stronger in a pure form than N-Heptane to clean microscope stuff. I used to consider ethanol safe and in a diluted state in most cases may be but I prefer not to risk it anymore. It also will dissolve balsam, where IPA won't, so I use it sparingly.

Understandable, after such an experience I would stay clear from ethanol too!
Though I've also had coatings getting damaged simply by using water and soft cloth and there have been any cases where improperly adhered coatings got "damaged" by mild cleaning solutions (I think Canon had a few really bad cases with some camera lenses - and let's not forget the issues many people had with MacBook display coatings).

As I said, I've never had an issue with modern coatings unless there was an underlying issue - though I am careful, only using Q-tips, no pressure and occasionally pointy paper roll tips for very difficult to reach spots. But I'll keep that in mind, especially for older lenses or ones where the coating is known have failed.

[PeteM]

Oxidized metal (rust, tarnish, etc.) won't clean up with typical solvents. And, as noted above, the most volatile ones can affect cements and coatings.

Since your glass is good and the damage is cosmetic, you might best consider it a sign of revered older age.

If it really bugs you (and occasionally it does me - either on a cheap microscope or one you hope to restore to some former glory), then very careful mechanical abrasion or cutting will be needed. If the end is plated brass, you also risk stripping what's left of the plating.

All that said, I've had success in mounting an objective on a parfocal extender > clamping the extender in a lathe collet > and VERY precisely cleaning up the metal. Sometimes by using a stiff folded corner of silicon carbide paper, sometimes with a fine diamond stone, sometimes with extremely light cuts. You need to be sure you can't inadvertently slip into the glass and also that no grit or chips come in contact with it. If you're left with bare brass, you might want (again, VERY precisely) brush on a thin clear coat.