Trying to Prevent Filter Glass Oxidation #1

[ulf]

In a confined volume purged with a suitable quality gas there will not be very much water left to react with the glass and when bound into the material there will not be any left for further reactions.

It is all about what you want to reach. You can not completely remove all the water by purging with a dry gas, but if you can reduce the amount enough to stop the deteriorating process it will be enough.

 

Remember that the alternative of free storage has an almost infinite source of water that eventually will eat your filters completely.

[colinbm]

I am trying some things out & including the gas, but it will take perhaps 6 to 12 months to get results.

A coating still seems the simplest & least intrusive.

[colinbm]

Manfrotto has shown they can put a water & dirt repellent on glass for $22, where some of the others want $200-400 to do the same.

[ulf]

I am trying some things out & including the gas, but it will take perhaps 6 to 12 months to get results.

A coating still seems the simplest & least intrusive.

Good luck finding something like that to a reasonable cost.

You might get an used lab sputtering setup for a couple of thousand dollars, but you have to find a suitable material to sputter and learn to do that without affecting the optical properties.

[colinbm]

The Chinese BG glass is 1/10th the price & is lasting better, it will be included in the test.

[Andrea B.]

Hey, everybody!! You all are still over here talking about gases, but I started a new topic about my rediscovery of the First Contact red polymer film.

 

You "paint" it onto a clean filter, it forms a film which can be easily peeled off. This might be the way to go for filter storage. Please go look for the link to red polymer film in this Topic: The AHA! Moment #2 about Preventing Filter Deterioration

[Andrea B.]

I also want to mention the following.

 

Simple filter coatings do not last forever either. So while a coated filter may have more longevity, it is not guaranteed. The dichroic filters which have "coatings" made by electronic sputtering are probably less prone to chemical deterioration.

 

However....(isn't there always a "however"??)....every coated filter I've ever had is prone to scratches & dings in the coatings. That of course may lead to eventual deterioration in the substrate.

 

Because I work outdoors a lot, my filter set always shows new scratches at the end of a season. I'm not careless, I'm not clumsy, but stuff happens!

 

I also want to report to you that filters can also deteriorate in dry climates. Where I live the humidity is routinely below 15-20% and often lower than that in the summer. Inside the house it sometimes gets to 5% humidity. And guess what? My filters *still* oxidize.

 

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I want everyone to walk away with the thought firmly in mind that there is no Magic Answer to this problem of filter glass degredation. The Best Practice is simply Routine Inspection and Maintenance.

[Andrea B.]

And remember also that my Kolari UV-Pass filter oxidized.

 

And my ZBW1 oxidized.

 

And one of my B+W blue-green filters oxidized.

(Sorry I don't remember its number right now.)

 

And ALL my blue and blue-green BaaderU color bandpass filters oxidized. The blue one also got the slimy pox thing.

 

ALL FILTERS DETERIORATE OVER TIME WHETHER COATED OR NOT.

 

I'm getting upset with the tenor of some posts in this topic.

 

If there is even one more tiny little bit of snark, then there will be a lock. And that upsets us all.

I've cleaned up some of it.

[colinbm]

Thanks Andrea, yes the problem is wide spread, but please remember that the major camera companies use a similar BG for their UR / IR blocking filters & they last the lifetime of the camera without oxidising.

[dabateman]

Thanks Andrea, yes the problem is wide spread, but please remember that the major camera companies use a similar BG for their UR / IR blocking filters & they last the lifetime of the camera without oxidising.

 

Not fully true. Look up problem with Kodak and Leica sensors.

My Kodak SLR/n had 0.8mm S8612 on the sensor. Just imagine the problem after a couple of years. People did need to do full disassembly cleaning.

Leica also well known to have issues.

 

Not to say its a rampid problem, but does happen.

 

Since I want that light at 300nm or even less, I make the decision to buy uncoated glass. If you only want UV-A, thats very easy with more durable BG39. Or medical grade coated filters.

[dabateman]

There are other glass types.

But S8612 is 60% transmission at 350nm

BG39 is 40% transmission at 350nm

BG61 is 20% transmission at 350nm.

[SteveE]

Why doesn't the substantial amount of water in the hydrogen peroxide that we have access to react with the phosphorous pentoxide and make things worse when soaking the filter, instead of cleaning it?

[colinbm]

Thanks SteveE, I would like to know this too.

I do know that the H2O2 is converted back to H2O on exposure to UV, that is why it is in a brown bottle, to block the UV.

I think that the liquid H2O molecules are too big for a reaction with the BG glass & that they need to be smaller in a vaopur, before a reaction takes place, BUT I am not a Chemist.

[dabateman]

Why doesn't the substantial amount of water in the hydrogen peroxide that we have access to react with the phosphorous pentoxide and make things worse when soaking the filter, instead of cleaning it?

 

I don't know, but have some ideas now after reading a bunch of papers that have studied liquid water versus humidity on storage canisters for nuclear waste.

In these studies liquid water increased the local mass, but humidity decreased it.

 

There is a surprising about of gasses and solid stuff dissolved in humid air.

 

But for us what I am guessing is that reaction time and mixing are the major players. We soak a filter for a week in water. It sits there, the hydrogen peroxide works on the deposit and we wipe it off. Not much stirring, and no rapid changes.

 

I will not clean a filter for 6 months, a year or a decade. That is many days exposed to water that is cycling. Water vapor deposits, causes damage and evaporates off. Then cycles again over many months.

What's in that humid air one day is different than an other as disolved organic matter changes and that too offers a variable to the corrosion and oxidation of the filter.

[Stefano]

Thanks SteveE, I would like to know this too.

I do know that the H2O2 is converted back to H2O on exposure to UV, that is why it is in a brown bottle, to block the UV.

I think that the liquid H2O molecules are too big for a reaction with the BG glass & that they need to be smaller in a vaopur, before a reaction takes place, BUT I am not a Chemist.

Molecule size is the same (I don't think there are quantum effects or something else).

 

Regarding H₂O₂, I think the problem is not the decomposition of it to form water, but rather the fact that it is almost never pure, and often diluted in water.

[ulf]

Molecule size is the same (I don't think there are quantum effects or something else).

 

Regarding H₂O₂, I think the problem is not the decomposition of it to form water, but rather the fact that it is almost never pure, and often diluted in water.

Liquid water do not behave as expected from it's molecule size H₂O. That is a rather small molecule size and low mass, compared to some organic liquids like many of the alcohols...

The water molecule is a dipole and as a liquid it combines in longer chains by the charge acting as a heavier substance.

 

Maybe the dipole property and smaller gas molecule size can be related to the filter problems and why exposure to liquid water is not harmful in shorter periods?

[colinbm]

Molecule size is the same (I don't think there are quantum effects or something else).

 

Regarding H₂O₂, I think the problem is not the decomposition of it to form water, but rather the fact that it is almost never pure, and often diluted in water.

 

Stefano, The H2O2 we are using is a domestic grade of 3%.

 

 

[Stefano]

Exactly, so it is basically water (97%) with a bit of hydrogen peroxide (3%).

[Bill De Jager]

You wouldn't want to use stronger H2O2 because it rapidly becomes dangerously reactive at higher concentrations.

[OlDoinyo]

I would say that Wood's-glass (including UG-type) and BG-type filters are definitely prone to this problem. But I would not go so far as to say that all filters are. I have had black-IR filters, B&W colored filters, polarizers and haze and skylight filters which have lasted years or decades with no trace of surface deterioration, even when stored in sub-ideal conditions. I wonder if it is a problem with metal content--UG glasses contain nanoparticulate nickel, if I recall corectly.

[dabateman]

No I think its a phosphorus based glass issue versus silica based glass issue.

All glass types which indicate more than 60 to 70% phosphorus seem to show oxidation within a couple months to a month depending on your humidity.

 

I have some silica based filters I have never cleaned, owned for 15 years and still look good.

My U330WB80 improved filter has some nasty oxidation on the back UG11 glass, but I have been nearly afraid to clean it. As its irreplaceable.

[ulf]

Manfrotto has shown they can put a water & dirt repellent on glass for $22, where some of the others want $200-400 to do the same.

Is that a one a piece service to be had?

Where to send in our filters for coating?

No offence, just joking.

 

I assume they have a mass-production set up for a batch process of big volumes of filters.

Then it is easy to cover the investment and research costs to do this.

[colinbm]

Thanks Ulf

I am aware that there are scales of economy here & filter companies are charging up to $200 for this type of treatment on plain glass UV cut filters, so why can Manfrotto do it so much cheaper ?

[dabateman]

If you want a safe coated filter like S8612. Just get a BG61. That stuff is coated and humidity resistant.

 

For all in UVA just get a Baader venus U filter. Mine has been excellent for nearly 12 years.

[JMC]

Given all this talk within the thread, it's prompted me to get my filters out again and check them all. A few observations;

 

My s8612 filters had some surface 'oxidation'. A quick clean with 3% peroxide and cotton buds got most if not all of it.

My Chinese 'BG39' one of those also was showing some surface 'oxidation'. Cleaning with peroxide solution removed some of it, but was not as successful as with the s8612.

Filter access was the biggest issue. Some filters I could remove the ring, but others, no chance without damaging them. And yes I was using the right tool. For those I couldn't removed I cleaned the best I could insitu, and that got me to within about 1-2mm of the edge. Not a huge problem for the single stack filters, but I have one which is 2 filters together, and I couldn't open that so could only clean the external surfaces.

 

All my filters are store in individual plastic cases, and usually with a small silica pouch too.

 

I shall certainly keep a more regular eye on them in future.