The S8612 is a "Class 3 Glass" which corrodes in the short term when not protected. The Data Sheet states that it should be used in a sandwich with Class 1 glass, such as BG38, to protect it from the environment. BG55 is a class 2 glass- " Long-term changes in the polished surface are possible under some circumstances."
NOW for real confusion: the individual Jan 2014 Data Sheet (STATUS: 01.12.2014) for S8612 lists it as a Class 2 glass, and it is clearly stated as a Class 3 glass in all other data sheets and the Schott catalogs. I Emailed Schott a long time ago about this. A revised Data Sheet shows it back as a Class 3.
The 1/2014 Data Sheet that disagrees with all the other data sheets.
It even refers you to the 2013 catalog, which clearly indicates it is Class 3. I've learned to download data sheets, look for revised data sheets, and keep all of them.
This is from the Schott optical catalog:
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).
SO- The difference between class 2 and class 3 is substantial. ONSEMI/SCHOTT/LEICA probably believe the coatings used on the BG55 filter are good enough to protect a class 2 glass, even if it did not work on a class 3 glass. The latter- my speculation. AND if they are wrong, and my BG55 filters ends up corroding, I'll send to you to make it full-spectrum.
If anyone wants this catalog-
NOW for real confusion: the individual Jan 2014 Data Sheet (STATUS: 01.12.2014) for S8612 lists it as a Class 2 glass, and it is clearly stated as a Class 3 glass in all other data sheets and the Schott catalogs. I Emailed Schott a long time ago about this. A revised Data Sheet shows it back as a Class 3.
The 1/2014 Data Sheet that disagrees with all the other data sheets.
It even refers you to the 2013 catalog, which clearly indicates it is Class 3. I've learned to download data sheets, look for revised data sheets, and keep all of them.
This is from the Schott optical catalog:
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).
SO- The difference between class 2 and class 3 is substantial. ONSEMI/SCHOTT/LEICA probably believe the coatings used on the BG55 filter are good enough to protect a class 2 glass, even if it did not work on a class 3 glass. The latter- my speculation. AND if they are wrong, and my BG55 filters ends up corroding, I'll send to you to make it full-spectrum.
If anyone wants this catalog-
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