Oxidation of UV ZWB2 filters?

Flashlight Modding and DIY Parts
1

I recently ordered and received some Chinese ZWB2 UV filters to use with my 365nm 3W LEDs from Epistar to get rid of the stray white light they put out and they seems to work very well.

However, I have seen some mentions of UV filters (in general) oxidizing over at ultravioletphotography.com. Supposedly you can easily clean the oxidized layer from the filter but I have some question about this:

  1. Does the oxidizing occur whenever the glass is exposed to oxygene, or only (or more so) if also exposed to UV light?
  2. Can you infinitely continue cleaning the glass to get rid of the exodized top layer?
  3. Do I understand correctly that the whole glass is permeated with the filtering material, ie. the filter is not just a coating that could eventually wear off by repeated cleaning?
  4. Can or should I take any precautions to protect the filters against oxidizing? Coating them with something perhaps (of course the coating should not contain UV blocking filters)?

My application is for use in a Halloween setup with a skeleton spray painted in fluorescent (not phosphorescent) clear transparent paint (it fluoresces in white).

I would have asked over at ultravioletphotography.com but they are very restrictive when it comes to applying for membership. Basically they won’t let you in unless you promise to be an active contributing member with a keen interest in UV photography.

2

I found little on the forum you linked and next to nothing when Googling.

Am I missing something?

You’d assume it would be common knowledge, especially here.

What I did gather is that you treat them as you treat pretty much everything you want to last, and unless they are poorly made, they’ll be fine.

Too high or low humidity seems to be able to cause delamination in poorly-made filters, but that’s all I’ve got.

3

I’ve seen crazy deposits on Hoya filters for shortwave lights but never on ZWB2. I don’t think it’s an issue. Long wave won’t solarize the filters either.

4

It’s discussed here for example:

Here as well:

Filter Care

Clean your filters carefully after use and before storage. Blow off any dust and particles with a bulb blower. Use a cleaning fluid that is made for use on coated filters. Clean and dry with a microfiber cloth or lens tissue because some coatings or special glasses are easily scratched

Dust, pollen, perspiration and contact with stronger acids or alkalines can damage filters. Some filters may deteriorate over time from solarization effects due to overexposure to Ultraviolet light. Chemical changes such as oxidation of the glass or of the coatings can also occur. And fungus can attack filter glass or filter coatings just as it attacks lenses.

If a filter becomes filmy or sticky or develops small crystals, clean it immediately to preserve it for future use. Oxidation on uncoated or unclad filters can be delayed by storing filters with dessicant packs. Using hydrogen peroxide or a fine-grade cerium oxide glass polish can remove light oxidation. Regular cleaning will prolong the life of all filters. Store filters as you would store your lenses - in a warm, dry place.

See more about filter care in the later section Filter Stacks: UV-Pass + IR-Block.

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Chemical changes such as oxidation can occur on uncoated glass. Oxidation can be delayed or prevented by storing stacked filters with dessicant packs. An overnight hydrogen peroxide bath or a cerium oxide glass polish can remove light oxidation. Regular cleaning will prolong the life of stacked filters.

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Remember that chemical changes such as oxidation can occur on uncoated, unclad glass used in filter stacks. Oxidation can be delayed by storing stacked filters with dessicant packs. Using hydrogen peroxide or a fine-grained cerium oxide glass polish can remove light oxidation. Regular cleaning will prolong the life of stacked filters.

Not sure how much of an issue this is, in particular for my application which does not involve shooting a photo through a UV pass filter but rather filtering the light from a 365nm LED for a Halloween prop. But I’d hate for my filters to go bad and become unusable within a couple of years due to lack of care and maintenance.

5

Offhand I’d say that comparing photography filters to flashlight filters is apples to oranges. Even if your filters get a few spots on them, you’re probably not going to notice, but those guys are using very specific wavelength high-quality filters, and the pictures will show every little flaw. You arent going to see that with your ZWB2 stuff on your led lights.

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6

My ZWB2 filters are years old now, and they do not show any oxidation. But I must say that they only get occasional use. I have broken a few and the black colour is throughout the glass, it seems not a coating, so rubbing it regularly should not be an issue. Only thing I noticed is that the glass is fairly brittle and it scratches easily.

7

Offhand I’d say that comparing photography filters to flashlight filters is apples to oranges

The filters as such are no different, at least they also use the ZWB2 filters for photography in addition to other, much more expensive, UV and other filters.

Obviously for my application a few minor blemishes are no problem. But if these filters do oxidize what starts out as a small spot will eventually cover the entire surface.

8

My ZWB2 filters are years old now, and they do not show any oxidation.

That is very encouraging. Mine will only be used one day per year, on Halloween. The rest of the year they will be stored in the attic. Looks like this is not something to worry about.