Remove coating from lens.

[Blord]

Does anybody know how to remove the coating of a G lens ? I have several lenses with a bad coating like stratches and burned surface. These lenses give a bad looking dots, flares and speckles around the dot. The coating need to be remove so that I can determine if it is the coating or the shape of the lens is damaged.

I have found that Hydrofluoric acid will dissolve the coating. You know that acid they used in Breaking Bad.
But this acid is not available anywhere here. Maybe there is a common household product that does the job.

Thanks
Kot

 

[Leodahsan]

Re: Remove the coating from a lens.

What is the coating made of?

If its MgF2, its soluble in nitric acid.
I don't know if it will dissolve, though. Its just an idea...

 

[steve001]

Re: Remove the coating from a lens.

Buy a new lens. It's safer.

 

[shokkunlasers]

Re: Remove the coating from a lens.

Leodahsan is right if it's MgF2 which is used for 300-600nm coating I would try it

Maybe somebody here knows which coating exactly is used that would help a lot.


You don't need hydroflouric acid it's hard to get and BTW I love Breaking Bad but
it really hurt how they showed it.
It ain't some super powerful acid it's weaker than concentrated sulfuric acid for example because Flour doesn't "let" H+ or better HO3+ ions "go" as easy.
They would have needed some rare experimental acid to dissolve things so fast
Other than that I was suprised how accurate Breaking Bad was.


I guess nitric acid hard to get in Belgium too
I know a way to make at home but it's difficult and dangerous
You could first try H2O2 c=30% with concentrated sulfulric acid.
That works also very good for dissolving strong bondings.
Anyway whatever way you chose play safe! Do it outside with safety glasses and gloves!

Vinz

 

[Leodahsan]

Re: Remove the coating from a lens.

Yeah if you're really up to a challenge, you can get red fuming nitric acid at home, you just need some sulfuric acid (boiling car battery acid, bought at automotive parts stores), some nitrate (NaNO3 is cheaper and easy to source, at least here) and chemistry glassware. :beer:

But, would a G lens without the coating be of any use? I mean, I think its the coating that makes a big difference... without it, its just an uncoated glass lens...

 

[NKO29]

Re: Remove the coating from a lens.

Yeah if you're really up to a challenge, you can get red fuming nitric acid at home, you just need some sulfuric acid (boiling car battery acid, bought at automotive parts stores), some nitrate (NaNO3 is cheaper and easy to source, at least here) and chemistry glassware. :beer:

But, would a G lens without the coating be of any use? I mean, I think its the coating that makes a big difference... without it, its just an uncoated glass lens...

AFAIK G9 lenses have NO coating, and they seem to have the BEST light transfer If they do have a coating then disregard this :beer:

 

[Blord]

Re: Remove the coating from a lens.

I have some G9 lenses harvested and they were a little damaged during the handling.
The local shop sells only Hydrochloric acid. It is a pretty common acid and it does nothing to the coating.
Well I could put the lens under the microscope and see exactly what causes the lens anomalies. I haven't done that.

I don't know if the G9 lens has a coating at all. If it does it looks very clear and transparent.

 

[shokkunlasers]

Re: Remove the coating from a lens.

Yeah if you're really up to a challenge, you can get red fuming nitric acid at home, you just need some sulfuric acid (boiling car battery acid, bought at automotive parts stores), some nitrate (NaNO3 is cheaper and easy to source, at least here) and chemistry glassware. :beer:

But, would a G lens without the coating be of any use? I mean, I think its the coating that makes a big difference... without it, its just an uncoated glass lens...

Yes that would be a possibility but nitrates are hard to get at least in gernamy because they always think you are going to make explosives with it

sulfuric acid with H2O2 could work and it's avaiable in some stores

I make HNO3 with NO2 gas and water

 

[grainde]

@ Blord if you want to try some HNO3 you can buy some "pickling paste" it is used to prevent stainless steel welds from corroding. You can buy it online, or from most places where they do welding. Often pickling pastes also contain a very small % of HF which probably wouldnt be a good idea on a lens, as it etches glass...So you could leave it outside for a few days for the HF to evaporate.

Edit @ Shokkunlasers HF might have a lower dissociation constant and therefore higher pKa than some of the "strong acids", but it does not mean that it isnt highly corrosive. If you get HF (aq) on your skin it will get absorbed into the tissue (skin) and destroy bone. It is apparently rather painless on the skin and doesnt leave many visible signs, it just removes calcium from the bones... Even small exposures can be fatal!
In most labs people are not allowed to work with it, unless they have had special training.

 

[shokkunlasers]

@ Blord if you want to try some HNO3 you can buy some "pickling paste" it is used to prevent stainless steel welds from corroding. You can buy it online, or from most places where they do welding. Often pickling pastes also contain a very small % of HF which probably wouldnt be a good idea on a lens, as it etches glass...So you could leave it outside for a few days for the HF to evaporate.

Edit @ Shokkunlasers HF might have a lower dissociation constant and therefore higher pKa than some of the "strong acids", but it does not mean that it isnt highly corrosive. If you get HF (aq) on your skin it will get absorbed into the tissue (skin) and destroy bone. It is apparently rather painless on the skin and doesnt leave many visible signs, it just removes calcium from the bones... Even small exposures can be fatal!
In most labs people are not allowed to work with it, unless they have had special training.

Indeed it is very dangerous and therefor not easy to get (which is good to protect unexperienced people like me) but it's not able to dessolve a whole human body within minutes like shown in breaking bad
and for this particular application sulfuric acid or other "strong" acids would have been better.

Sorry for being a bit off topic and confusing there. Blord mentioned Breaking Bad and HF

For removing a coating it's just unnessasary with nitric acid or sulfuric acid it's possibly IMO

 

[steve001]

Anti-Reflex Coating Stripper
Anti-Reflex Coating stripper,(AR Stripper)

 

[Blord]

Thanks for the link. The shop sells only in large quantities and I need just a few droplets.

 

[The Lightning Stalker]

Yes, hydrofluoric acid is used for glass etching. That would be absolutely the wrong thing to use. That coating stripper site says they use an "acid mix", so it might be something as simple as aqua regia. Wikipedia's acid article has a good list of different acids.

 

[Leodahsan]

Yes, hydrofluoric acid is used for glass etching. That would be absolutely the wrong thing to use. That coating stripper site says they use an "acid mix", so it might be something as simple as aqua regia. Wikipedia's acid article has a good list of different acids.

It have some information about safety regarding hydrofluoric acid. Maybe its on the composition of this "acid mix"?

 

[The Lightning Stalker]

They do say it is a weak mix. Etching depends quite a bit on the concentration of the acid, so maybe it's
weak enough that the glass dissolves evenly instead of etching. I'm sure they have done many
experiments to determine the optimum concentration which would not alter the optical properties of the
glass. It's also possible that it works by dissolving a thin layer of glass under the coating and not the
coating itself, similar to rust removal by electrolysis where some metal underneath the rust is removed,
loosening the rust.