First sign of oxidation on my ionic filter glass!

[Andrea B.]

The possibility of a sticky sugar coating from Coca-Cola turns me off the idea of using that! And I can't think what anti-oxidant Coca-Cola might have which would work like H₂0₂?

 

The hydrogen peroxide I just bought has a 3% concentration. In the US we can buy a brown opaque bottle of H₂0₂ in a grocery store or drug store (pharmacy) in the area where antiseptics are displayed. The solution is diluted with purified water.

 

Baking soda, baking powder? Never tried those. I'll look into it.

 

I also like cerium oxide. But it most certainly will remove a coating on a lens or filter. I know because I experimented! As Cadmium warns, use CeO₂ only on uncoated glass and be sure not to get an adulterated version. Look for optical grade from a reputable supplier.

 

Toothpaste? NO!! Most toothpastes contain silica which can scratch glass.

[Andrea B.]

I had to go review the following because I've forgotten a lot of basic Chemistry 101 from 40 years ago.

 

Baking soda is NaHC0₃, sodium bicarbonate. When mixed with water, it produces (eventually) NaOH, sodium hydroxide, and CO₂, carbon dioxide, in the form of bubbles. At first glance that sodium hydroxide, a.k.a. "lye", is a bit scarey. We know to avoid lye as a very caustic substance. But in dilute amounts it seems to be harmless? We all have used or at least heard of using a spoonful of baking soda in water for relief of an upset stomach, and none of us have gotten lye-poisoned from that.

 

As to what might be cleaning an oxidized glass filter when it is soaked in baking soda and water, I don't know. The lye? The bubbles? The temporary presence of the unstable intermediate carbonic acid, H₂CO₃?

 

Baking powder contains baking soda. (I had completely forgotten that!) Baking powder also contains potassium bitartrate, KC₄H₅O₆ (thank you Wikipee) which is the salt of tartaric acid. Eventually CO₂ bubbles are produced by this combo when heated. So I have the same question: what is actually cleaning the oxidation off the glass? I'm not sure. Any ideas welcomed on this.

 

I have not personally tried either baking soda or baking powder.

 

If the cleaner is somehow the CO2 bubbles, then perhaps plain seltzer water would be useful for oxidation?

[Andy Perrin]

Lye is used for making bagels and pretzels too. It’s not bad if not too concentrated.

[Cadmium]

I would stick with the hydrogen peroxide and/or white optical grade cerium oxide (real stuff, not from China).

[Andrea B.]

agreed!

 

But I'm still curious about what actual chemical cleans the oxidation if baking soda works. Next time I see that one of my blue-greens has oxidized, I will try it.

[dabateman]

According to the internet, which is nevee wrong. Sodium bicarbonate is a gental abrasive cleaner that will remove rust and oxidation. So may work the same way as cerium oxide, just cheaper.

I will have to test it out on my Ug5 filters.

[Andrea B.]

Yes, agreed, it is probably just the abrasiveness which is at work. But it wasn't clear above from those who had tried baking soda/powder as to whether they were dipping the filter in the bubbles or rubbing the soda/powder directly on the glass. "-)

[bvf]

Nope - I just soaked the filter overnight in a glass with some baking powder and water.

[Andy Perrin]

Nope - I just soaked the filter overnight in a glass with some baking powder and water.

Baking POWDER may work differently than baking soda? Just because the former also contains the latter doesn't mean they have the same mechanism for cleaning.

[bvf]

Quick update on this - my old U340 was developing a coating again. The baking soda approach cleaned it up a treat. A few teaspoons of baking soda stirred into a small glass of water, and lest the filter in it over night.

 

Baking powder (as opposed to baking soda) seemed to work OK as well when I tried it some time ago.

[Andy Perrin]

Haha, interesting. I still want to see someone try Coca Cola. Not me.

[ulf]

One way to reduce or avoid these problems are to always store the filters in a dry place when not in use.

From https://www.schott.c...on-2015-eng.pdf:

 

"After a certain amount of time, the surface of highly sensitive glasses exhibits a

slightly cloudy residue. Initially, this residue can be removed using glass polishing

compounds. More severe attacks ruin the surface polish quality, however. This

effect is caused by humidity. With respect to this behavior, the color filter glasses

can be classified into three groups:

 

Group 1

No substantial surface change occurs in most of the optical filter glass types.

These types are not identified specially in the “Properties” brochure.

A change in the surface is only possible under extreme conditions, if subjected

to a continuous spray of sea water, or if used in rain or water.

 

Group 2 Symbol:

For the optical filter glass types BG18, BG40, BG50, BG55 and all KG glass types,

there is virtually no long-term change when used and stored in moderate climates

or in closed work and store rooms (constant temperature below 35°C, relative

humidity less than 80%). A desiccant should be used if the possibility of wetting

exists. For use and storage in open air and tropical climates, it is advisable to apply

a protective coating which SCHOTT can provide upon request.

 

Group 3 Symbol:

For the optical filter glass types BG42, UG5, UG11, BG39, S8612, S8022 and S8023

a change in the glass surface is possible after a few months of normal storage.

For this reason, applying a protective coating or lamination is recommended for

durable optical filter glass from Group 1 (SCHOTT can provide both)."

---

I keep my filters in air-tight boxes with a bag of silica gel, when they are not used:

 

 

I prefer the blue type of indicating silica gel, like this:

https://www.ebay.co....y4AAOSwRS9d4fIy

The container-pouch in the filter storage box is a re-sealable tea-bag.

Then the box's dimensions and volume can be minimised as the pouch's shape is flexible.

That is nice both for carrying around many filters and to get a small volume of humid air to dry out after I have used the filters.

 

The oxidation is accelerated by humidity and temperature and I try to not have the boxed filters in a too hot environment for long periods.

[Andy Perrin]

Where did you get that filter holder? I love that.

[SteveE]

I keep my filters in air-tight boxes ...

 

I worry about long term storage of lenses and filters in plastic containers. In cars, after awhile you get a cloudy film on the inside of the windshield. This is from outgassing of the plasticizers and other compounds from the plastic inside the car. This would not be good for a lens, especially if it got to the inner lens elements.

[ulf]

Where did you get that filter holder? I love that.

I designed and 3D-printed it.

It is built by sections, one for each filter and also thicker end walls.

There are also three internal M3-threaded spacers.

 

The spacing between the walls is tailored to match my filters with the Xume rings attached.

It is not very difficult to change the spacing and create new .stl files.

[ulf]

I worry about long term storage of lenses and filters in plastic containers. In cars, after awhile you get a cloudy film on the inside of the windshield. This is from outgassing of the plasticizers and other compounds from the plastic inside the car. This would not be good for a lens, especially if it got to the inner lens elements.

That is a good point, especially when things get hot like inside a car in the sun.

I'll keep my filters in their airtight boxes during this off season to see if there is a problem with these boxes. If so, next year's hibernation-place will be in glass jars instead.

[Andy Perrin]

I haven't got access to a 3D printer or I would give it a try.

[dabateman]

I tried the baking soda in water trick to clear the oxidation on my 1mm Ug5, 3mm ug5 and 2.2mm BG39. The oxidation on my Bg39 filter was fresh and it removed it. However, I bought my Ug5 filters with oxidation on them almost 2 years ago and it removed some, but not all.

I will have to try hydrogen peroxide on them to see if that works.

[Andrea B.]

Leave it in the H₂O₂ overnight. I usually try for 24 hours when using H₂O_2.

I use a little glass bowl and cover it with a larger inverted bowl.

[Cadmium]

Yep, that is what you do.

1) take the glass filter out of the filter ring.

2) put it in hydrogen peroxide (household strength, usually 3%, easy to find in any drug store, might have to ask for it in some countries).

3) let it soak for days if you want in covered container. I use a jar with a screw on sealed lid.

4) take it out, clean it with PEC pad or microfiber cloth.

5) clean it with alcohol.

6) look for any remaining crud.

7) polish with cerium oxide if need be.

8) return to filter ring.

[Andrea B.]

I am sooooo lazy. I've never taken the filter out of the ring to do this.

 

Thank you for reminding everyone about this! It is good practice.

[Cadmium]

I would take them out of the ring, especially if the labels are adhered. Hydrogen peroxide might loosen the label, and cerium can get into the smallest places.

Best to remove the glass, clean it all up good before you reassemble it.

Filters are valuable, and some are rare and hard to replace.

 

I had a couple Schott BG24A filters, 2mm and 3mm, and they are no longer made, hard to find (similar to BG3 and BG25, but not exactly), fairly discontinued, out of production.

They had crud built up on them, very cloudy, would not come off with cloth.

Took them out of the rings, soaked them in my jar with Hydrogen Peroxide for a few days,

took them out, scrubbed them with PEC pad, they were clean as a whistle, look brand new.

 

That was all I did, but they could use a nice polishing with cerium also.

 

 

BG24A 5mm + S8612 1mm

[dabateman]

Additional update on my oxidized UG5 filter.

Well I left the 1mm one in baking soda for almost a week. It got some oxidation off, but not completely and not on both sides. I had it in a small plastic sealled container. I wasn't careful when removing it, so I don't know if the side it did clean was down in the extra baking soda or the top side.

So whipped it off and placed it into a plastic container with 3% hydrogen peroxide.

After 24hrs there was some removal of oxidation on the other side.

So left in for additional 24hrs and looked today.

That line about only wipping off the baking soda solution maybe critical here.

But today noticed that no additional oxidation has been removed.

What I did see were many new glass etching marks over the surface.

 

I think I may have generated sodium hydroxide in the switch, which will eat glass.

So if anyone plans to use hydrogen peroxide, make sure to fully rinse a filter off with water (ideally distilled water), prior to placing it into hydrogen peroxide.

 

Interesting on the web it says one of the best ways to remove small glass etching, which I now have. Is to make a paste of baking soda and rub the glass. I might try that to see if that works or just polish with cerium oxide as I have that too. The latter is optical grade so should be better.