How to remove anti-reflection coating?

[Ajemsa]

I have a small glass lens which has an anti-reflection coating that has deteriorated and is cloudy. I'm not wanting to put much effort into this lens but does anyone know how I can remove the anti-reflection coating without damaging the glass substrate? I'm guessing a solvent of sorts would do it.

[Satchmo]

The coating would need to be polished off I'm afraid. Not cost effective !

[el_draco]

I'd use dilute HCL. you can get 4mol stuff at Bunnings. Used for cleaning bricks. Watch your skin though.

Rom

[nebulosity.]

I cleaned the coatings off some binocular objectives using some mild aluminium cleaning acid.

Jo

[Ajemsa]

Co-inicidently, I was cleaning my paving with some HCL the other day - I have some left over. I will give this a go to start. Thanks Rom.

Jo, how would I go about getting aluminium cleaning acid? Is there a particular brand?

Mark, I was half contemplating getting some cerium oxide. You would probably know better than most, could you rub this on by hand without causing too much damage to the glass?

Thanks everyone.

[MortonH]

Only a semi-serious response here:

In researching the Baader and Lunt solar wedges recently I came across a post from someone who put a filter in FRONT of the solar wedge and, in his words, "baked the coatings clear".

I'll leave it to those with more technical & optical knowledge than me to say if this was just stupidity or has any validity to your situation.

[el_draco]

I reckon you would be using HCl to clean Al as well.... Anything else is a bit dangerous.

[ZeroID]

Any idea what the metallic content of the coating actually is ?
Al (Aluminium) is removed by NaOH ( Caustic Soda or Drain Cleaner). A very very diluted solution might be an option although I think you would be advised to dissassemble the EP so it didn't migrate back into the body.
Sulphuric Acid (H2SO4) could be available from an old car battery, a couple of drops would be more than enough. Copper, Zinc and other metals are susceptible to that one. Again dilute well and dissassemble.
HCl you have already covered.

Wash well and rinse a few times after if you go down any of these paths. None of them will attack normal glass elements but I can't vouch for more exotic lens.

[Ajemsa]

Unfortunately, I do not know anything about the lens but I will definitely be removing it out of the cell.

I had a go with HCL on a different lens I had but it seems like it had almost no effect on that coating and probably made the exposed glass worse. I'll try again soon enough.

[5ash]

Found this post on cloudy nights, Not sure of the chemistry involved looks like a bit of serendipity . Anyway here it is:

"This is what I did for the corrector on an old 10" Meade LX3 our club got to remove the coating.

1) I cleaned it good with Dawn dish washing liquid and a soft cloth. Rinsed with distilled water and dried it.
2) I then soaked it several days in Ferric Chloride (This is printed circuit board etching solution you can buy it at Radio Shack). I would go and agitate it every few hours. I replaced the Ferric Chloride after the first day.
3) Rinsed well with distilled water.
4) I then soaked it in muriatic acid (purchased at Home Depot) for about 15-20 minutes and kept agitating it. I took it out several times and rinsed it to check the progress.
5) Rinsed well with distilled water.
6) Let it soak in a solution of baking soda and water to neutralize any remaining acid.
7) I cleaned it again with Dawn dish washing liquid and cotton balls. Rinsed with distilled water and dried it.

I used a shallow plastic tub with a snap on lid, some rubber gloves and a plastic funnel.

I did not get it recoated, I just installed it as is and it works well. I believe the cost for recoating was around $125 per side."


Hope this helps philip * *

[Ajemsa]

Thanks Philip.

I had some luck with the lens that I was trying to repair. In preparation of doing some acid cleaning, I opened the lens cell and found that one of the internal surfaces had an almost oil-like coating on it. This cleaned off fairly easily returning the lens to a very usable state. I was initially convinced that it was one of the outer surfaces.

Prior to this, I used the the hydrochloric acid on a different lens and over a period of 24 hours it was practically destroyed. That lens won't see the light of day let alone the light of a star. The acid had no affect on the glass dish it was in though.

I suppose it is difficult to know the best approach unless you really know what glass you have to start with.

[blink138]

i worked at hoya lens australia as their optical technician for many years in the 80's and 90's and at this time there were still a lot of glass opthalmics, mainly their hi-index 1.7 and 1.8 indices
occasionally a multicoat was stripped for whatever reason and i know it was an acid bath, however the composition of the liquid i never enquired about
i do think however that a soft rotary buff could take the coating off as it being glass it will not "wave" the surface
the glass multicoatings are a magnesium fluoride if i recollect (mgf2)
pat