The Fungus Among Us

[smieglitz]

I recently acquired a couple old Darlot lenses that have a bloom as well as dendritic fungus growing on them. I'm sure the glass has been etched a bit by this growth.

I'm thinking I might be able to polish them a little and perhaps improve the optical quality. I'm thinking of using whiting which is powdered calcium carbonate (much softer than glass) to do so. I have heard a similar compound in a cleanser (Bon Ami or was it Barkeeper's Friend?) used to be used to polish automobile windshields. Anyone else recall something like that?

Would there be a better alternative? The glass is pretty trashed so I figure I don't have much to lose trying this, but any tips would be appreciated.

Joe

 

[JG Motamedi]

Joe,

I used rottenstone, pretty much the same abrasiveness as whiting to clean a very stubborn haze off an uncoated lens. It worked where Alcohol, MEC, and other nasty solvents did nothing. No scratches I noticed. Obviously this would be for non-coated lenses like your Darlots only, as I am sure this would really demolish the coating.

 

[johnnywalker]

How about some of the abrasives that rockhounds use to polish their stones? I believe the ones they use on the final polish are very fine. Not sure what they all are or if it would work - aluminium oxide is one I think, another is a very fine diamond grit - but it may be worth talking to a gemologist or a shop catering to rockhounds about.

 

[df cardwell]

rottenstone is great for a quick polish on the glass before you put it into the frame. Probably be good for trying to salvage the old lens.

Stay away from the Celors..

 

[ggriffi]

You might something like this...

I recently acquired a couple old Darlot lenses that have a bloom as well as dendritic fungus growing on them. I'm sure the glass has been etched a bit by this growth.

I'm thinking I might be able to polish them a little and perhaps improve the optical quality. I'm thinking of using whiting which is powdered calcium carbonate (much softer than glass) to do so. I have heard a similar compound in a cleanser (Bon Ami or was it Barkeeper's Friend?) used to be used to polish automobile windshields. Anyone else recall something like that?

Would there be a better alternative? The glass is pretty trashed so I figure I don't have much to lose trying this, but any tips would be appreciated.

Joe

Joe,

Many years ago astronomy was one of passions, so I built an 8 inch reflector telescope. You might try using one of the finer polishing compounds. here is a link to a general astronomy page for kits.

Astronomy Kits

Hope this helps.

g

 

[fparnold]

Just a quick note: if you go the telescope polishing materials route, my old book on the subject mentions that cerium oxide polishes much more quickly than jeweler's rouge. This also means that it will de-optimize your optics rather quickly if you get aggressive with it.

Let us know how it turns out.