29 replies to this topic

[ultrainfra]

Hello everyone,

I came across something that works similarly to a desiccant packet, except it absorbs oxygen instead. You can find them on amazon here.

I didn't see anything when searching for oxygen absorber here on UVP, so many might not be aware these exist. When combined with a desiccant, I hope that these will help preserve the longevity of my recently purchased U-360 & S8612 filters (once the endless rain stops and there's sunlight, I hope to take some pics to share!).

I hope this is useful!

Edited by ultrainfra, 13 November 2020 - 05:30.

[Cadmium]

I am no chemist or expert about what happens with filter surface 'oxidation', but I think it may be a bit more complicated than the word we use, "oxidation", or oxygen...
Perhaps it has more to do with water than oxygen. Who was it here a while back that posted about the material formula for some of the filters that are most prone to surface corrosion,
but the inference was that a certain elements in the glass melt are prone to chemical reaction to water. I think it was phosphorous, wasn't it.
Yes, here is the material safety data sheet for S8612, scroll down to 16.1, see the high percent of phosphorous in the glass melt?
The same high percent of phosphorous is also present in all the other easily corroded filters, some U filters, etc..
By the way, U-360 isn't one of the filters that is particularly prone to surface corrosion. UG11 and U-340 are prone though.
https://www.schott.c...?tenant=ao-cert

I have some of that AR coated S8612 now, you know, but it was a 'small' batch and costs twice the price of of uncoated.
Additionally, the AR is centered at 365nm (unlike a usual AR centered in the visual range at 550nm),
so it should potentially optimize any U glass UV-only (UV pass) stack transmission, like for example U-360 2mm + S8162-AR 2mm.
However, the non-coated can be easily cleaned every so often and kept in good condition for less money.

Edited by Cadmium, 13 November 2020 - 05:51.

[ultrainfra]

Cadmium, on 13 November 2020 - 05:12, said:

I am no chemist or expert about what happens with filter surface 'oxidation', but I think it may be a bit more complicated than the word we use, "oxidation", or oxygen...
Perhaps it has more to do with water than oxygen. Who was it here a while back that posted about the material formula for some of the filters that are most prone to surface corrosion,
but the inference was that a certain elements in the glass melt are prone to chemical reaction to water. I think it was phosphorous, wasn't it.
Yes, here is the material safety data sheet for S8612, scroll down to 16.1, see the high percent of phosphorous in the glass melt?
The same high percent of phosphorous is also present in all the other easily corroded filters, some U filters, etc..
By the way, U-360 isn't one of the filters that is particularly prone to surface corrosion. UG11 and U-340 are prone though.
https://www.schott.c...?tenant=ao-cert

I was wondering what it was that made some glass prone to oxidation, interesting. Curious though that in section 9 it says no oxidizing characteristics. Also, the phosphorous is already an oxidized state according to that sheet. I looked up the CAS number on the data sheet. The form of Phosphorous oxide used is phosphorous pentaoxide, a powerful desiccant. The reaction it forms with H20 produces phosphoric acid, which can be rather sticky. See here. So, I suppose what we are calling oxidation is more properly called hydrolysis (just like you suspected).

Thanks for the info, now I was able to narrow down exactly what makes some of these glass materials degrade. I'm no chemist either, know just enough to comprehend what I am reading due to it being part of a grad school course.

Edited by ultrainfra, 13 November 2020 - 06:06.

[Cadmium]

I don't know the aspects of phosphorous myself, but it is true that all of the filters I can think of that have such surface problems over time have high amounts of phosphorous in the material mix.
I think it was David that come up with that idea.
You sounds smarter than me about the chemistry pertaining here.
The AR coating should be interesting to observe over time. No idea yet how well it will work for maintaining the surface,
but it will increase UV transmission, some anyway.
Looking straight through it, to the eye, it looks the same as the non-coated version. It has a slightly different light reflection to it when viewed at a certain angle under the right lighting.

I also got some Schott D263, the stuff I got is very thin, like thick paper, 0.15mm, and can be glued on the surface for protection. It is very inexpensive.
Interesting stuff, I have not used it for an thing yet.

However, even without any kind of surface protection, such glass can be cleaned up with common household 3% hydrogen peroxide by soaking and scrubbing.
I have had very good results with that, even with some filters that were unattested to for years. Cerium Oxide polish is also good.
I have some special equipment for that, but it can be easily done with your finger.

Edited by Cadmium, 14 November 2020 - 05:41.

[Cadmium]

Wowa! Changed your pic!
When you get a flower (preferably yellow) with a pattern, I would be interested in that U-360 2mm + S8612 1mm example, Landscape would be good too, but might not illustrate 700nm leak as well as a flower.

[dabateman]

That profile picture reminds me of Speed Grapher, an Anime series.

Cadmium,
I saw the S8612 coated. Boy that did get pricey. I think I have blown my budget with recent purchases.

[Cadmium]

A nice big bottle of %3 hydrogen peroxide costs less than $2...

[Andrea B.]

All glass is subject to oxidation over time.

Glass is hygroscopic. It attracts and holds water due to ingredients such as sodium oxide or other soluble oxides.

The water on the glass surface causes oxidation by leaching alkali ions out of the glass. (Some alkali ions are more easily leached out of glass than others.)

Chemically, hydrogen in the water replaces an alkali ion in an oxide to form a hydroxide. The surface of the glass is weakened by this leaching and the corrosion can spread and new chemical reactions can be induced.

The chemical equation would look like this if magnesium were being leached from glass: MgO + H₂O → Mg(OH)₂
[Please note that I myself do not know if magnesium, per se, is easily leachable from glass by water. I simply wanted to remind everyone of what the oxidation process looks like in chemical equation format. The end product here is a nice antacid, magnesium hydroxide. ]

---

REFERENCE: https://en.wikipedia/wiki/Glass_disease
This reference is interesting because it mentions later stages of glass deterioration. For what we typically encounter with some of our color filters, please see State One under the heading States of Deterioration. I note in passing that the writers of this particular Wikipedia entry do not mention hydrogen peroxide baths for State One deterioration. But then, they are writing primarily from a museum conservator point of view.

REFERENCE: See also https://en.wikipedia/wiki/Corrosion#Corrosion_of_glass
Link from Alaun.

REFERENCE: Optical Filter Glass - Schott AG
This downloadable PDF is just full of info about glass and glass filters. I'm sure we have referenced it in the past, but there's the link again.
I will specifically call your attention to the following: Section 5.5, page 24. The bolding is mine.

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
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
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).

---

Let me remind everyone that the recommended lamination (or cladding) with other glass has certain drawbacks. And protective coatings are not perfect either.

Keep your uncoated, unclad filters clean and dry. Inspect them often. Clean them the very second you observe any deterioration.

---

I've been trying to think through whether or not using an oxygen absorbing packet would help with the moisture problem when storing filters. I don't really know.

[Andrea B.]

woops, lost a link above to the Schott reference. Will fix it.


Fixed.

[ultrainfra]

Andrea B., on 15 November 2020 - 01:16, said:

woops, lost a link above to the Schott reference. Will fix it.


Fixed.

That is some good information. Thank you. Seems like there's more than one thing going on (potentially, depending on the particular glass).

[Cadmium]

Other than these few filters below, you need not concern yourself with oxidation.
Here is a simple list of filter glass types to keep an eye on and maintain:
Schott UG5 (Hoya U-330)
Schott UG11 (Hoya U-340)
Schott S8612
BG39 (BG39 is a poor choice for UV stacking, it suppresses IR the same as S8612, but does not transmit UV as well as S8612, so get S8612 instead of BG39)
also S8022, S8023 (neither of which would you be likely to use).
So that is 3 types you need to think about, the rest are not really used, unless you use BG39, in which case you are reducing your UV transmission. If you use BG39, then 3+1 types.
Personally, I can't think of any reason to own BG39 or use it for anything, it is simply an inefficient second compared to S8612.

As you can read below,
Schott BG40
Schott KG types
However, these are not as prone, "...virtually no long term change...moderate climates...".

So that is a total of 5 filter glass types that you might be likely to use, and would want to keep an eye on.
Get some hydrogen peroxide, or cerium oxide, and clean these filters above when you see any small cloudy spot that will not come off with a cloth, and you will be fine.

Note is says, "caused by humidity".

Edited by Cadmium, 15 November 2020 - 12:58.

[Cadmium]

There are dehumidifying chambers, adjustable humidity and temperate, I imagine they could get expensive.
They would hold a lot of stuff, a lot of equipment if you want. I don't think desiccant in a filter box is going to prevent deterioration, it may slow it down, and how long will the desiccant last, some humidity will still get to the filter.
Some dehumidifying chambers don't use desiccant.
OK, crazy idea, just saying.

Edited by Cadmium, 15 November 2020 - 08:22.

[Alaun]

The better terminus to describe the deterioration of glass might be corrosion. If you look up corrosion in the english wikipedia, you find some nice explanation of glass corrosion

[Cadmium]

Alaun, Thanks!
https://en.wikipedia...rosion_of_glass

[Andrea B.]

Cadmium, you repeated what I copied from the Schott PDF !!
*****

Alaun, thanks for that link to add to the others!! I'm going to put it into my comment above also.
*****

Something else I learned from reading about "glass disease" or "glass corrosion" is that museum conservators have discovered that glass can be kept too dry, which can also be harmful to old glass which has already developed aging problems. So they try to maintain a stable humidity and temperature.

We, of course, will probably not attempt stable humidities for our filter glasses. Too expensive!!
*****

BTW, it is not just uncoated, unclad filters which are prone to clouding - although as Cadmium points out those are most likely to develop preliminary corrosion. I wanted to remind everyone that my Kolari filter has needed a hydrogen peroxide bath also.

[Cadmium]

Andrea B., on 15 November 2020 - 19:26, said:

Cadmium, you repeated what I copied from the Schott PDF !!

Sorry, I wanted a hard copy in my post to illustrate the list I made, which is the point of my post, that the list of filters prone to surface deterioration is quite limited.
A list of about 5 filters that anyone here is ever likely to use, and only really about 3 of those are going to be more important to watch more closely,
basically UG11 (U-340), UG5 (U-330), and S8612. Those are the three that will be most prone.

Just trying to show how uncomplicated this is, it is simple, and a small list.
I have a lot of various uncoated and coated filters, many date back to who knows how many decades even,
and personally, I have never seen any surface deterioration on any filters, other than dirt, grime, and slug slime... (that rhymes!), coated or uncoated, except those mentioned above
(and a few of the old used eBay purchased adjustable filters, those are weird, and some of those show a lot of age acquired color anomalies).

Edited by Cadmium, 16 November 2020 - 01:16.

[Andrea B.]

Added: My BaaderU blue filters are notoriously bad for clouding up.

[Cadmium]

Andrea, I was wondering if that Krylon spray on Slug Slime would actually seal filters and prevent deterioration?

Disclaimer: OK people, that was a joke, perhaps an inside joke, but ask Andrea for the full story if you want. I was not being serious.

[dabateman]

That story is proof that Andrea was abducted by aliens. Simply not being able to account for a long period of time is strange.
Now we accept aliens. But don't call them UFOs in the sky. Those are for crazy people. The correct term is UAP, unidentified aerial phenomenon.

"The U.S. Department of Defense (DoD) announced the creation of a task force to analyze and understand the "nature and origins" of UAPs. The Department of the Navy, under the cognizance of the Office of the Under Secretary of Defense for Intelligence and Security, will lead the Unidentified Aerial Phenomena Task Force (UAPTF).

The mission of the UAPTF "is to detect, analyze and catalog UAPs that could potentially pose a threat to U.S. national security," DoD officials said in a brief statement released on Friday (Aug. 14)."

[Cadmium]

David, It isn't recommended that you put the Slug Slime Spray in your coffee.