Cerium oxide

[Fandyus]

If you read my previous post, you might have seen me talking about the fact that my ZWB1 has developed spots that won't go away even after I soaked it for days in hydrogen peroxide. I wanted to see if I could possibly fix it by scrubbing it with Cerium oxide instead, but I don't really know how it works.

I'm sorry if there is a tutorial on here somewhere, in that case can someone please just direct me to it?

I'd like to know about the toxicity of cerium Oxide and about the general risks of scrubbing the top layer of the exotic glass substrate. I'd like to know how to scrub the filter correctly, also if someone could tell me where one can generally buy Cerium oxide (links appreciated). Thanks.

[colinbm]

In that previous post I mentioned about using Phosphoric Acid to clean the worse of the gunk on the ZWB filters, then a final clean with Hydrogen Peroxide.
It just needs a soak for half an hour, in Phosphoric Acid in a shallow dish & should scrub off with an old tooth brush. A slight smear will remain that the Hydrogen Peroxide will clear.
Cerium Oxide is just a final polish if you want.
This has worked fine for me on troublesome Chinese ZWB.
It is used by labs to clean Transilluminators that have been stored too long.

[Fandyus]

2 hours ago, colinbm said:

In that previous post I mentioned about using Phosphoric Acid to clean the worse of the gunk on the ZWB filters, then a final clean with Hydrogen Peroxide.
It just needs a soak for half an hour, in Phosphoric Acid in a shallow dish & should scrub off with an old tooth brush. A slight smear will remain that the Hydrogen Peroxide will clear.
Cerium Oxide is just a final polish if you want.
This has worked fine for me on troublesome Chinese ZWB.
It is used by labs to clean Transilluminators that have been stored too long.

Thanks, any idea which stores could sell phosphoric acid?

[Andrea B.]

I just wrote on the other topic about being careful with phosphoric acid. It is quite corrosive in its usual strength. Also I would like to know how one disposes of used phosphoric acid? Wouldn't it be a pollutant if added to a community drainage system?

 

While writing that, it pinged into my head that you might try Coca-Cola which has some phosphoric acid??

 

Cerium oxide is safe. It is routinely used for glass polishing. You rub it around on the corrosion, then rinse it off. For a filter, you want to use a grade of cerium oxide which is made for glass polishing (very fine particles). You can buy the powder and mix it yourself or buy a prepared paste.

Here is a random link to show you what to look for:  LINK

Also ask Cadmium whether he still has any for sale.

[ulf]

It is used in many different fields from rust stripping and priming for metal plating to in food.

An American very sweet beverage that comes in curvy bottles with a red label contains phosphoric acid. 41 mg per 250ml. I do not know if that is strong enough, but I would prefer a more pure diluted solution.

Maybe Colin  know the strength of the liquid he used?

 

You might find it in a place selling paint, hardware or hobby stuff for plating etc.

It might also be interesting when renovating old rusty cars.

 

If you get concentrated acid it is diluted by pouring the acid into water, not the opposite way around. 

 

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In general it is good if people here note the concentration of different things. Please do so in the future.

The hydrogen peroxide in concentrated form is very dangerous i it can be bought at all.

For filters it is the 3% diluted that is the right one.

[Fandyus]

1 minute ago, Andrea B. said:

I just wrote on the other topic about being careful with phosphoric acid. It is quite corrosive in its usual strength. Also I would like to know how one disposes of used phosphoric acid? Wouldn't it be a pollutant if added to a community drainage system?

 

While writing that, it pinged into my head that you might try Coca-Cola which has some phosphoric acid??

 

Cerium oxide is safe. It is routinely used for glass polishing. You rub it around on the corrosion, then rinse it off. For a filter, you want to use a grade of cerium oxide which is made for glass polishing (very fine particles). You can buy the powder and mix it yourself or buy a prepared paste.

Here is a random link to show you what to look for:  LINK

Also ask Cadmium whether he still has any for sale.

The disposal and general toxicity/corrosiveness issues concern me about phosphoric acid too. I am not a trained chemist so I would rather refrain from handling dangerous chemicals if possible. Thank you for the link! I'll also ping cadmium. In case I order online I will probably have to find a different store though, since shipping through Amazon is very expensive here in the Czech republic.

[ulf]

Coca-Cola is very acidic, much more so that lemon juice or vinegar, but it is masked by heaps of sugar.

[ulf]

For polishing filters it is important that you get quality stuff.

Cadmium used to sell that. 

[ulf]

Phosphoric acid is easy and safe to dispose of.

Just dilute it with water and pour it out the drain.

The name make it sound bad for the nature, but it is not, at least in reasonable quantities.

For filter cleaning, I'd guess the remains would not need to be diluted at all.

 

[Fandyus]

Thanks a lot for the information, Ulf. Appreciate it. Thankfully I know the famed rule about diluting water with acid and not the other way around from chemistry class still

[colinbm]

Phosphoric Acid is considered mild, used gloves & it can be safely disposed in our small use down the drain.
It is sold in automotive stores as a rust converter, converting rust to phosphorous, which is water resistant & paintable.
Pure Phosphoric Acid is a gel like consistency, 85% is fairly liquid, but it will leave a slightly sticky surface, that is compatible with Hydrogen Peroxide.
Those who know me Know I have had trouble with filters in a humid environment & this works a treat.
As I said it is used by Labs to clean Transilluminators.
Nothing extra special is needed, just a little soak & a light rub down, followed by a wash in hydrogen peroxide.
Give it a try, success is guaranteed.

PS, Remove the ZWB glass filter from the metal filter ring.

[Fandyus]

7 minutes ago, colinbm said:

Phosphoric Acid is considered mild, used gloves & it can be safely disposed in our small use down the drain.
It is sold in automotive stores as a rust converter, converting rust to phosphorous, which is water resistant & paintable.
Pure Phosphoric Acid is a gel like consistency, 85% is fairly liquid, but it will leave a slightly sticky surface, that is compatible with Hydrogen Peroxide.
Those who know me Know I have had trouble with filters in a humid environment & this works a treat.
As I said it is used by Labs to clean Transilluminators.
Nothing extra special is needed, just a little soak & a light rub down, followed by a wash in hydrogen peroxide.
Give it a try, success is guaranteed.

PS, Remove the ZWB glass filter from the metal filter ring.

Honestly, the last line might be a showstopper, I don't know how. But thanks for the other information!

[Andy Perrin]

The filter ring unscrews. You need something that fits in the little notch on the edges (they make a tool for it) but a pen will work in a pinch. 

[Wayne Harridge]

3 hours ago, Andy Perrin said:

The filter ring unscrews. You need something that fits in the little notch on the edges (they make a tool for it) but a pen will work in a pinch. 

Yep, something pointy usually works ok, really depends on how tightly it was screwed in manufacture.

 

 

[ulf]

A simple caliper can be used too. The upper part for measuring inner diameters works well.

[Andy Perrin]

Just don't make the mistake I did one time and screw the filter ring back in upside-down, with the notch facing towards the filter! I had an interesting time getting the ring back out after that...

[ulf]

13 hours ago, ulf said:

Coca-Cola is very acidic, much more so that lemon juice or vinegar, but it is masked by heaps of sugar.

Phosphoric acid sounds toxic as it is some kind of chemical, but it is used as an ingredient in many types of processed food.

To avoid that bad impression there are additive declarations by E-numbers (in Europe only?).

Phosphoric acid is E338, found in normal Coca-cola and Coca-cola-Zero. I checked in the store today.

 

TBD if Coca-cola-Zero is strong enough to cure filter corrosion

[Wayne Harridge]

Here's a link to what you can clean with coca-cola: https://www.airtasker.com/blog/15-ways-clean-coca-cola/ - unfortunately oxidised glass filters wren't mentioned!  I've seen demonstrations of how well it cleans up copper, brass and other copper alloys (thinking coins here) and I used phosphoric acid years ago for preparing stainless steel prior to soldering.  I'd give it a try on those filters, just make sure to rinse it well with warm water then you can hit it with the hydrogen peroxide.  Is this oxidation of the filter itself or a coating applied to the filter?  I've heard of a few lenses that suffer from a deterioration of the coatings leaving a diffusing film on the lens which is difficult to remove except with cerium oxide. 

[GaryR]

Thanks for the info on Phosphoric acid Colin!

An inexpensive watch wrench works perfectly for disassembling filters.

[colinbm]

Wayne, the ZWB filters have phosphor in the mixture of the glass that reacts with the humidity in air.
 

[enricosavazzi]

On 8/6/2022 at 7:15 AM, Andy Perrin said:

Just don't make the mistake I did one time and screw the filter ring back in upside-down, with the notch facing towards the filter! I had an interesting time getting the ring back out after that...

For this type of work it is useful to have a collection of rubber corks/stoppers of different diameters. Press one of the right diameter to the ring while twisting it (usually counterclockwise to unscrew). Friction does the job. A firm but not excessive pressure is sufficient even for stuck rings that cannot be turned by hand. Unless I cannot find a rubber stopper of the right size, I prefer to use stoppers rather than the double-pronged metal tools. The latter can easily damage aluminium rings.

 

I have a set of about 20 stoppers (of different diameters top and bottom) and use them all the time for stuck filters and adapters. Sets of stoppers of silicone rubber of the right diameters are designed to work with photographic filters (these sets save space since you can nest the smaller stoppers into holes in the large ones). Often they also have concave top and bottom, so you can use them to unscrew the retaining rings of convex lenses. Ordinary rubber stoppers for chemistry labs also work, but the range of diameters may not be that great and their top and bottom are usually flat. A rubber mat to put on the tabletop also works, except when the ring to unscrew is recessed.

 

Tools designed to change air filters in cars can be used on the metal barrels of lenses and other optical equipment. They use a rubber strap and a plastic handle to apply friction, and do not scratch the equipment. A set of two or three is all that is needed, since the length of the rubber strap can be adjusted.

[Andrea B.]

This is a very good suggestion to use rubber corks or stoppers to unscrew filter retainer rings.

Thank you, Enrico !! 

 

I have some of those metal "calipers" for unscrewing lens parts or filter rings, but yes you can all too easily scratch with them.

[ulf]

These are made for lens and filter rings:

https://www.amazon.com/Sizes-Lens-Filter-Wrench-Rubber/dp/B00988D1BK

[Fandyus]

Alright, despite the phosphoric acid recommendation, I have decided to also try cerium oxide, since it's good to have options. I looked at eBay (since Amazon shipping is way too expensive here) and I found several listing such as this. Problem is that none of the sellers list the average particle size like they do on the Amazon link. I already asked two what the grade is but I'm wondering if 2.5 microns is the maximum recommended size for my uses or if the particles being a bit bigger is no issue.

I want to get the cerium oxide partially also because I have a ZWB3 that has oxidized to an extreme degree and I want to see if I can fix it, I figure mechanical agitation might be better at that than acid, but that's just my uneducated estimate.

[dabateman]

I think Cadmium also had some luck using a sonicating bath filled with hydrogen peroxide to clean up some filters. These are typically used to clean up jewelry. 

I am not sure if others tryed that though.

I have just used hydrogen peroxide and cesium oxide, purchased from Cadmium.  You gave to be careful polishing.  I polished my 1mm UG5 with too much force,  and cracked it in half. The two halfs still kind of work,  but I have to be carefull holding it.