biginovero
Established
I tried to strip a front lens of a yashinon 50mm 1.4 from the sixties of its coating.
A telescope maker who was ready to remake it in its telescope making facility advised me to do so.
he told me that a weak solution of nitric acid (a 65% solution dulited 1:9, i.e 10 cc to 90 cc of water) would take more than a week to strip the lens of its coating.
well in about eight minutes of imemrsion i had frosted glass, with deep furrows especially in the front face.
Glass appears perfectly white.
A professional chemist told me it shouldn't have been so, glass is insensitive to acids.
A telescope maker who was ready to remake it in its telescope making facility advised me to do so.
he told me that a weak solution of nitric acid (a 65% solution dulited 1:9, i.e 10 cc to 90 cc of water) would take more than a week to strip the lens of its coating.
well in about eight minutes of imemrsion i had frosted glass, with deep furrows especially in the front face.
Glass appears perfectly white.
A professional chemist told me it shouldn't have been so, glass is insensitive to acids.
Dante_Stella
Rex canum cattorumque
Laboratory glass might be insensitive to acids, but lenses are made with different materials (usually rare earth elements) that change the refractive index and are sensitive to a lot of things.
Mackinaw
Think Different
Dante’s got it. Focal Point (John Van Stelton), who does lens repair, will polish off old lens coatings rather than using chemicals, just for this reason.
Jim B.
Jim B.
biginovero
Established
I must conclude that telescope lenses are a different thing.
That old telescope maker that advised me is a professional, so he must have been sincere.
Pity, in any case I may already have found some replacement parts from a broken one.
JoeV
Thin Air, Bright Sun
Are you certain the old telescope maker wasn't talking about stripping silver or aluminum off front surfaced mirrors?
x-ray
Veteran
I have a degree in chemistry and nitric acid should not damage glass. It sounds like you had hydrofluoric acid which will frost glass and even the vapor will.
x-ray
Veteran
Thinking about it Id say it probably was a reaction of the dilute nitric acid with the coating material itself not the glass. Depending on the actual material used to coat the lens there certainly could have been a reaction. Some of the early coatings were a permanganate vapor coating which could react.
Most coatings are only a molecule or so thick so polishing the lens should fix the problem. Even if the acid reacted with the glass it would only occur on the surface unless it was allowed to remain in contact for some time.
Ive worked with quite a lot of concentrated nitric acid and it was always stored in glass bottles and I've never seen glass etched by it.
Most coatings are only a molecule or so thick so polishing the lens should fix the problem. Even if the acid reacted with the glass it would only occur on the surface unless it was allowed to remain in contact for some time.
Ive worked with quite a lot of concentrated nitric acid and it was always stored in glass bottles and I've never seen glass etched by it.
biginovero
Established
Exactly what a professional chemist (40 years of experience with acids and a restorer of old weaponry cleaned with depotentiated acids) told me.
The only think I remember having done previously was cleanng the front surface thoroughly with isopropyl.
Ah, coming home I found the lens almost totally dissolved.
I could put my hands within the solutions with only a faint hint of sting..
biginovero
Established
I feel I will never try this cleaning in the future. We cannot have datas concerning such treatments, I think only a few retired engineers in Japan or Germany might have some useful info, go figure.
I was advised also to use cerium oxide, I didn't perform it being afraid of altering the lens surface's shape, I just don't remember wether this happens or not.
many years ago i had access to old issues of sky and telescope and I saw many examples of homemaking of telescope lenses, cerium oxide was the final polishing stage, if somebody might assure me it is not altering the shape I will gladly get it next time.
In any case for a real heavenly intervention I have just bought the front group for this same lens from ebay, it even has a close serial number.
sevo
Fokutorendaburando
Optical glass will differ considerably from lab or household glass in its chemical properties. Down to actually water soluble elements (though these often are technically not glass but crystal), which sometimes are used inside cemented or tightly sealed groups.
Hydrofluoric acid is quite unusually hazardous and poisonous - I'd be surprised if you could somehow "accidentally" get hold of that nowadays, when even plain old nitric acid is a controlled substance...
Hydrofluoric acid is quite unusually hazardous and poisonous - I'd be surprised if you could somehow "accidentally" get hold of that nowadays, when even plain old nitric acid is a controlled substance...
Alpsman
Well-known
You can ruin ordinary silikatglass with Hydrogenfluorid acid.
ChrisLivsey
Veteran
We are sure that lens element is glass are we and not an optical resin element which would react as you describe?
It is not easy to etch glass with nitric acid, the conditions you used were more benign than this:
boiling the glass in a 70% nitric acid solution for 30 min is more effective in the reduction of sodium,calcium, and aluminum atoms at the surface of the glass than other etching methods with nitric acid.http://scitation.aip.org/content/avs/journal/jvsta/19/1/10.1116/1.1333087
and you had that result leads me to conclude the element was not glass and it was extremely unlikely you had hydrofluoric acid which is hard to obtain and liberally labelled with dire warnings when you have it, I have had occasion to dispose of the stuff and can attest to its nature first hand.
It is not easy to etch glass with nitric acid, the conditions you used were more benign than this:
boiling the glass in a 70% nitric acid solution for 30 min is more effective in the reduction of sodium,calcium, and aluminum atoms at the surface of the glass than other etching methods with nitric acid.http://scitation.aip.org/content/avs/journal/jvsta/19/1/10.1116/1.1333087
and you had that result leads me to conclude the element was not glass and it was extremely unlikely you had hydrofluoric acid which is hard to obtain and liberally labelled with dire warnings when you have it, I have had occasion to dispose of the stuff and can attest to its nature first hand.
x-ray
Veteran
After reading that he cleaned the lens with alcohol that was my thought too.
To the op, a word about safety, don't stick your hand or any part of your body in even dilute nitric acid. You're obviously not trained in the safety aspects of strong acids and can seriously injure yourself if not handled correctly. Seriously, you put your finger or hand in the acid and made a judgement on strength by how much sting it caused. This is extremely dangerous!
David Hughes
David Hughes
Hi,
If/when you get the replacement parts I'd wonder, in your shoes, if they were glass or plastic. The old trick is to feel the lens on your cheek; glass is cold but plastic isn't.
Regards, David
PS Is there some simple test for the acid; meaning to show what type it is?
If/when you get the replacement parts I'd wonder, in your shoes, if they were glass or plastic. The old trick is to feel the lens on your cheek; glass is cold but plastic isn't.
Regards, David
PS Is there some simple test for the acid; meaning to show what type it is?
ChrisLivsey
Veteran
The brown ring test is specific for nitric acid but you are going to need Ferrous Sulphate and Conc Sulphuric acid which probably rules it out as simple for a darkroom set of chemical availability.
Easier to test the lens than the acid
JoeV
Thin Air, Bright Sun
Not only is HF dangerous to handle (skin contact can result in fluorosis of the bones, as it has an affinity for minerals), but you shouldn't mix nitric acid with alcohol, they call that rocket fuel.
biginovero
Established
Chemistry lessons were a pro forma at my school, we were more concentrated on linguistic and logic abilities.
To be sure, I ever consult my chemist friend before doing anything (I actually have two). The elder one told me that such weak acid is not so dangerous for a very, very quick dip.
As for the lens being plastic, well, in effect it wasn't so cold in my hands.
It was also feather like in weight.
I also have a fungused beyond repair doublet in my cellar (infected lens storage area ...)
I will dip in the same solution to see the effect on both the lenses and the cement.
x-ray
Veteran
I'm not trying to be rude but I'm always concerned about people messing with dangerous mayerials they have no clue about. You obviously haven't the foggiest clue.
Are you mixing the 1:9 solution from the concentrate?
Do you realize that dilution is strong enough to damage your corneas almost instantly.
Are you wearing goggles or even better a face shield. How about rubber or nitrile gloves.
If you're mixing are you adding water to the concntrated acid or acid to the water?
Are you labeling it and keeping it locked away from children?
biginovero
Established
hm, my friend told me differently. In any case i'm not interested in playing with chemicals, if not strictly necessary.
I know that my friends who make damascus knives regularly use this acid to etch blades and it seems they use no special care.
i had bought it for the same purpose.
But we are in Lombardy where people build stuff in factories with a lack of precautions that might scandalize other populations.
Must be the legacy of our gallic ancestors .....
Bill Clark
Veteran
I don't understand why the coating should be removed. The lens on a camera would make a pretty small refractor telescope. The other use could be the monocular device which provides a wider angle view than the main telescope lens, that's used to get into the vicinity what you're after to view with the telescope.
And, to me, I can learn alot, explore, have fun, whatever on the internet from the easy chair I'm sitting in with my iPad. Check out NASA, JPL, Hubble just to mention a few. Hubble is a pretty nice telescope.
I made several reflector (Newtonian) telescopes in the 1960's from kits I bought from Edmund Scientific. They put together a kit of the various grits and two glass pieces, one used for grinding, the other, made from Pyrex, that would be the final mirror. I used an empty 55 gallon drum placed on end to serve as a work place to grind the lens and I made a template to fit on the lid of the drum to hold the glass and walk around while grinding. I had a firm in St. Paul that would, in a vacuum, coat the mirror and, as I remember, used aluminum. No acids were ever used to make a reflector telescope, at least I never used them.
Here is some info:
http://www.skyandtelescope.com/astronomy-resources/four-infamous-telescope-myths/
https://spectrumscientifics.wordpre...ngs-why-they-are-important-and-what-to-avoid/
Please read the first sentence.
At any rate, acids can be a problem, many problems. Here in Minnesota I'm sure the folks at the EPA would not be too happy using this acid stuff.
And, to me, I can learn alot, explore, have fun, whatever on the internet from the easy chair I'm sitting in with my iPad. Check out NASA, JPL, Hubble just to mention a few. Hubble is a pretty nice telescope.
I made several reflector (Newtonian) telescopes in the 1960's from kits I bought from Edmund Scientific. They put together a kit of the various grits and two glass pieces, one used for grinding, the other, made from Pyrex, that would be the final mirror. I used an empty 55 gallon drum placed on end to serve as a work place to grind the lens and I made a template to fit on the lid of the drum to hold the glass and walk around while grinding. I had a firm in St. Paul that would, in a vacuum, coat the mirror and, as I remember, used aluminum. No acids were ever used to make a reflector telescope, at least I never used them.
Here is some info:
http://www.skyandtelescope.com/astronomy-resources/four-infamous-telescope-myths/
https://spectrumscientifics.wordpre...ngs-why-they-are-important-and-what-to-avoid/
Please read the first sentence.
At any rate, acids can be a problem, many problems. Here in Minnesota I'm sure the folks at the EPA would not be too happy using this acid stuff.