Holmium oxide glass?

[Andrea B.]

Look in its MSDS for the composition of a particular filter glass.

Example PDF: Technical Safety Information BG39 - Schott AG

Then you can figure out which alkalis might be part of the corrosion and

try to determine whether they are toxic or not.

---

Here is a brief description of how the glass oxidation occurs.

(Originally posted elsewhere in 2020.)

• 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.
  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.
  (That is magnesium hydroxide, a harmless compound used as an antacid.)
  

---

Referring to the BG39 MSDS above, you can see that one ingredient in BG39 is arsenic trioxide. Arsenic is not an alkali so I don't think it is leachable from glass during a simple water induced oxidation process. However, that phrase about "new chemical reactions" which can be induced after the glass has been weakened by oxidation gives me some concern that toxic, non-alkali ingredients like arsenic might eventually "escape" the original mix over time?

 

Yah, for sure, do not lick corroded filter glass.

But like yuck, who would do that???

[Andrea B.]

P.S. I found it a bit strange that the MSDS for Schott UG5 made no reference at all to water induced oxidation of that blue-green glass. In section 9.1 listing some physical and chemical properties of BG39, the item "oxidizing characteristics" equates to "none". Really? Maybe they are talking about something else besides the corrosion we see on our blue-green filters?

 

In Section 7 about handling and storage of BG39, the "conditions for safe storage" are

• Store in dry environment.
  
• Avoid excessive humidity.
  

So there is that.

But it would have been nice if we were told why we should do that.

Oh well.

[Fandyus]

Thank you all for the information. I see I have done well to always wash my hands after touching the filters, but now I am also glad to know that it should be enough.

[ultrainfra]

I have one. It's nothing to write home about. It gives a bit of a warmth to images. It looks very much like an old lens that had thoriated glass which yellowed over time. Nothing really interesting for IR photos that I've seen so far but I haven't had much time to play around with it (I just got it recently)

[Fandyus]

On 9/14/2022 at 8:03 AM, ultrainfra said:

I have one. It's nothing to write home about. It gives a bit of a warmth to images. It looks very much like an old lens that had thoriated glass which yellowed over time. Nothing really interesting for IR photos that I've seen so far but I haven't had much time to play around with it (I just got it recently)

One year and one day later, I see this comment. Kind of funny. Found anything out since then?