cerium oxide for haze removal?

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Dan Daniel

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Thought I'd see what people think about using cerium oxide to remove heavy film or haze on lens elements.

I was working on a Mamiyaflex that had a haze on the front of the rear element. Looks almost like soap film on a bathroom mirror? A little mottling, etc. I tried: xylene; acetone; naphtha; Eclipse lens and sensor cleaner' ROR lens cleaner. Each one tested for maybe a couple of minutes rubbing with a cotton swab. The element is in a brass mount so I can't just soak an isolated glass element. Nothing changed.

I then put some ROR on a cotton swab, dipped the swab in some cerium oxide powder, and hand-"polished" the surface. After a minute or so the haze was reduced. With about 5 minutes of polishing, the glass was clean. No obvious coating loss. Haze gone.

All light polishing, not scrubbing. Just swirling the swab around with the oxide slurry.

Part of my thinking is that with such a light, slow swabbing, the chances of me changing the shape of the glass itself is pretty minor. Especially with a 65 year old lens, probably polished on machines with less than perfect tolerances.

Haven't shot with the lens yet, which is the real test.

Any thoughts? Mistake? Thanks.
 
If you could change the lens shape with a cotton swab and anything short of iron filings I'd be impressed :) . Nice job , did you perchance take any before and after pics ? Peter
 
Did something similar with a Mamiya 55mm TLR lens. Nasty haze that wouldn't come off and killed contrast. I was worried about changing the element shape so I made a mould of the surface using epoxy. Cerium oxide did the trick although it left lots of micro scratches (likely from the mould). Contrast was restored.
 
Before you start delaminateing lens coatings and pitting soft glass, contact DAG or another noted repairers since they may use proprietary solutions to dissipate haze.
 
I've brought back a bunch of lenses from the hazy dead using cerium oxide. I use either a cotton swab or a rubber glove and my finger, depending upon how large a surface I'm polishing. For those of us who take our time and know what we're doing, this is more expedient and far less costly than sending a lens off to a technician, who will probably be doing the same thing. For haze that can't be removed, it could actually be lens blooming, which can only be removed with cerium oxide. There is no worry about changing the profile of the surface unless you intentionally set out to do so; and that takes a very long time. Just rubbing a little bit of paste around in a swirl, evenly, until the paste seems to clear itself off, will not change the lens surface shape. We're talking about an abrasive that can slowly remove coating, which is incredibly thin, so there's little worry about changing your lens unless you set out to do so.

Phil Forrest
 
I did a few experiments with polishing. They were lenses that would otherwise disappear in the ashtray. My experience is that polishing is very labor intensive. And after polishing the lens parts can become very clean and neat. But now the disappointment. There has been some optical changes due to thinning of the lens and it has become completely useless for photography. So still put in the ashtray.
 
It will almost certainly be fine. I polished the front element of a Summar that looked like someone had used it to grind gravel into sand - it was damn near opaque. It's fine now, but then I have no interest in taking diagnostic photos of brick walls or measuring ultimate resolving power, so take that assessment as you will.
 
Thanks for the varied responses.

I have a lens that I will be working on soon and will try to get photos of the kind of 'soap scum' I am talking about.

I am not trying to remove coating scratches or glass scratches. And I am not talking about the kind of fog/haze that I have seen on, say, some Leica lenses. I just cleaned up an old Zeiss biotar that had fungus and haze, but solvents and lens cleaner handled that smoothly. This really is more like soap scum, a mottled whitish coating on surfaces. I've done a lot of polishing of acrylic, and even taken scratches out of plate glass, so I have some idea of what kind of pressure and time it takes to truly reshape materials. That's not how I see what I am doing, but it could happening anyway.

Well, more later. Thanks again.
 
I think that since you were able to tell there was no coating damage, that ought to guarantee there was no change to the shape of the lens or its formula. I didn't know Cerium Oxide was something you can buy! Where does one get it?
 
I managed to revive a Mamiya 65mm TLR lens that was totally opaque on the rear element by rubbing it with a cotton swab dipped in toothpaste. The lens is usable now though it is still lower contrast than the unaffected lens. I assume toothpaste to be less abrasive than Cerium Oxide, so it could be a good place to start if you are hesitant about damaging a lens.
 
Toothpaste is much more abrasive than cerium oxide, only because the grit is much more coarse. I use a cerium oxide paste that is for polishing telescope mirrors. To the fingers it feels like a lubricant, but it definitely cuts glass.

Phil Forrest
 
Phil_F_NM said:
Toothpaste is much more abrasive than cerium oxide, only because the grit is much more coarse. I use a cerium oxide paste that is for polishing telescope mirrors. To the fingers it feels like a lubricant, but it definitely cuts glass.

Phil Forrest
Click to expand...

Interesting, I assumed because toothpaste companies claim not to polish your enamel. I may need to order some of this stuff to give it a try.
 
Rob-F said:
I think that since you were able to tell there was no coating damage, that ought to guarantee there was no change to the shape of the lens or its formula. I didn't know Cerium Oxide was something you can buy! Where does one get it?
Click to expand...

It's used in rock and gemstone polishing. I ordered a small amount on eBay.

I forgot to photograph it, but just took some 'sludge' off of a an Autocord lens element. Again it wouldn't come off with any liquid that I have. And again, the lens coating doesn't show obvious signs of having been removed.

For 'fun,' I took some of the cerium oxide to a lens element with obvious coating marks- 'cleaning marks' as people call them. After twice as long of polishing as I have done on any 'sludge,' I saw no improvement in the coating mark and no sign of it changing. So I am heading to the cerium oxide maybe being good for sludge, dried oil deposits and such. And not for removing coating marks. Beyond that, I doubt that I will ever get into trying to reshape a lens, remove a real scratch in the glass, etc.

I'll try to remember to take photos when I do a Yashicamat lens element in the near future.
 
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