How do you clean the surface of objective

[osterport]

One annoying thing for us is, some old objective metal surface is being corroded like this. I tried to use alcohol cloth to clean it, not working.

[apochronaut]

One annoying thing for us is, some old objective metal surface is being corroded like this. I tried to use alcohol cloth to clean it, not working.

That one has lead a rough life!
Unfortunately , the paint used on those is susceptible to many solvents and rubs off easily, so cleaning has to be done carefully but fortunately those optics will still be in perfect shape. I bought a Reichert 40X 1.0 planapo oil w./iris for 75.00 in the last year that looked like it had been stored in a salt mine and it cleaned up well. Perfect stellar optics. I've had about 30 examples of Reichert Austria infinity 45mm objectives. All were at least 25 years old. Not a single one had bad optics or oil invasion

You can use a fine metal polish. In North America there are a couple of fine abrasive products sold for polishing silver. Two I know of are Cameo and Silvo. There are also products sold for polishing chrome in car shops. Similar products are likely around everywhere. The abrasives are very fine, for polishing.
First, mask off the top and bottom lenses, with tape or plug if you prefer.i
Put the polishing product on a cotton swab to carefully polish around the remaining painted areas. You can even use a toothpick. The broader unpainted barrel can be done with a small wad of cloth or tissue, or the swabs, or a toothbrush. Then buff with the cloth or swabs, being careful not to buff over the paint because you may remove more of it. You can do a final light cleaning over the paint with ipa. Those little corrosion pustules can be reduced by 80-90% and the satin chrome, brightened up quite a bit.
To stop further deterioration of the painted letters once everything is cleaned and brightened up, you can either put a precision cut cover of matte, clear tape over the entire side wall of the objective, or mask off the top, bottom, and threads, then spray a coating of clear matte lacquer.
Both work well. The taping is finicky because you need to get the circumference exact and cut the tape perfectly so the butt edges meet exactly. If it is done well, you cannot tell it is there unless you look really closely. The taping needs to be executed exactly before you put it over the paint because if you try to remove it, it will likely remove the paint with it. Place the seam AFTER a painted area, line it up and slowly wrap it until you come to paint, then assess for alignment because at this point you can still remove it if is cockeyed. Never try to remove it if it is over paint.

[osterport]

One annoying thing for us is, some old objective metal surface is being corroded like this. I tried to use alcohol cloth to clean it, not working.

You can use a fine metal polish. In North America there are a couple of fine abrasive products sold for polishing silver. Two I know of are Cameo and Silvo. There are also products sold for polishing chrome in car shops. Similar products are likely around everywhere. The abrasives are very fine, for polishing.
First, mask off the top and bottom lenses, with tape or plug if you prefer.i

Thanks apochronaut ! Reichert objective is covered by chrome and it's brass inside, right? My concern is, when we polish it, the fine particle may get into lense even if it's covered by tap of something else. Liquid metal cleanser can be easily wiped off, will it be better?

[apochronaut]

Yes, it is brushed chrome on brass. In my experience, liquid metal cleaners I have tried have limited ability to remove the staining on the chrome caused by whatever type of corrosion has taken place. They just brighten up the relatively clean metal that is corrosion free.The process that I described is the way I do it in order to clean corroded areas.

[PeteM]

If you happen to have access to a lathe, another option is to mount the objective in an RMS extension, hold that extension in a collet (or chuck if you're super careful and have a long RMS extension), and then use very fine (600 grit or so) silicon carbide paper. It's easily controllable, quick, and will take off the blistered spots of chrome.

Of course, then you have shiny brass spots left where the chrome is gone, regardless of which polishing method is handy for you. If you don't like that look -- and have always wanted to own a labeler, Brother makes P-touch labelers with up to 1" wide tapes, including silver color with black print. You could sort of restore the look and the identification of your objective that way. The tape is pretty durable, about as good as the original paint.

[thomasfrank]

I understand the frustration of dealing with corrosion on the objective lens of a microscope. While alcohol wipes can be effective in removing some stains, they are not the best solution for corrosion protection.
bitlife

[osterport]

Yes, it is brushed chrome on brass. In my experience, liquid metal cleaners I have tried have limited ability to remove the staining on the chrome caused by whatever type of corrosion has taken place. They just brighten up the relatively clean metal that is corrosion free.The process that I described is the way I do it in order to clean corroded areas.

I tried this one "metal polish", it can polish some stains off the surface, the paint real requires caution! I would need a small tool to clean the stain around the paint.

[apochronaut]

It already looks 80% improved. Quite deftly done. I have used a flat sided toothpick ( not the round pointed ones) around the paint to apply a bit of metal polish here and there, and a clean one to buff it. Lightly wipe any residue with ipa.
Bic and probably others make a " Sharpie Pen" with a very fine tip. Not the same as a "Sharpie Marker" You can reconstruct many of the letters and numbers with one of those reasonably well, or someone skilled with a fine (00 or 000) brush can use paint. Once done and thoroughly dry, wrap it in matte tape as mentioned earlier, keeping the butted seam off of the painted characters and always, one wrap only, once the tape is over the characters.
I considered using clear shrink wrap but never tried it, mainly because the tape works well enough.

I don't have that exact objective but I have a 2.5X. That would show the exact markings to copy except for the mag. and N.A. values. It looks like some of yours are missing entirely. I will see if I can get a photo of that posted a.s.a.p. or perhaps you can find an image on the web. I took a brief look but could not find one. A lot are still in daily use.

[osterport]

It already looks 80% improved. Quite deftly done. I have used a flat sided toothpick ( not the round pointed ones) around the paint to apply a bit of metal polish here and there, and a clean one to buff it. Lightly wipe any residue with ipa.
Bic and probably others make a " Sharpie Pen" with a very fine tip. Not the same as a "Sharpie Marker" You can reconstruct many of the letters and numbers with one of those reasonably well, or someone skilled with a fine (00 or 000) brush can use paint. Once done and thoroughly dry, wrap it in matte tape as mentioned earlier, keeping the butted seam off of the painted characters and always, one wrap only, once the tape is over the characters.
I considered using clear shrink wrap but never tried it, mainly because the tape works well enough.

I don't have that exact objective but I have a 2.5X. That would show the exact markings to copy except for the mag. and N.A. values. It looks like some of yours are missing entirely. I will see if I can get a photo of that posted a.s.a.p. or perhaps you can find an image on the web. I took a brief look but could not find one. A lot are still in daily use.

With this small wool felt brush, I further clean it up, looks quite ok, even though it's not yet perfect. I dare not clean it around the paint.

By the way, do you have a picture of the fine brush to reconstruct the letters?