mazdaro Posted October 8, 2023 Share #1 Posted October 8, 2023 (edited) Advertisement (gone after registration) Basically, there are three ways for a successful removal: a) Purely physical treatment b) Chemical treatment followed by physical treatment c) Purely chemical treatment (US Patent) ad a) Usage of a polish (Ceroxid, Nigrin for Glass, Ajona and even cigarette ashes have been proposed). This treatment method may fail if the radius of the lens will be changed (Uneven abrasion)!! The great advantage of the purely physical method lies in the additional removal of fine scratches! ad b) Usage of a mixture of Isopropanol and salt water (Concentration?) followed by scraping with a synthetic scraper: https://www.koalaeye.com/blogs/our-stories/how-to-remove-coating-from-glasses ad c) Short treatment with NaOH conc. (Saturared solution) followed by rising with water and another short treatment with HNO3 conc. Of course, you have to wear safty googles and you have to work under a hood or in fresh air: Always pay attention: When solving NaOH (s) in water, a hudge amount of heat is generated, and HNO3 has a toxic pungent smell! And don't mix these reagents!!!😉☠️ https://patents.google.com/patent/US2536075A/en Normally, such aggressive compounds (strong acids and base solutions) are stored in glass bottles and even heated in glass flasks. Except for HF, bases are more aggressive to glass. That's why plastic bottles are preferred. I don't know to what extend optical glass is also largely inert to concentrated acids and bases (Short application time). In any case it should be inert to Acetone. According to Wikipedia the solubility of MgF2 is as follows: Soluble in nitric acid Slightly soluble in acetone Insoluble in ethanol Does anybody have experience with this topic? Regards, Roland Edited October 8, 2023 by mazdaro Link to post Share on other sites More sharing options...
Advertisement Posted October 8, 2023 Posted October 8, 2023 Hi mazdaro, Take a look here How to remove an inhomogeneous coating (MgF2) from a frontlens (e.g. Summicron). I'm sure you'll find what you were looking for!
mazdaro Posted October 9, 2023 Author Share #2 Posted October 9, 2023 I've got the chemicals now. I will report...😀 Link to post Share on other sites More sharing options...
mazdaro Posted October 9, 2023 Author Share #3 Posted October 9, 2023 Acetone and Ethyl acetate are ineffective. Tomorrow I will try the base/acid method. Link to post Share on other sites More sharing options...
AndreasG Posted October 9, 2023 Share #4 Posted October 9, 2023 vor einer Stunde schrieb mazdaro: Acetone and Ethyl acetate are ineffective. This was to expect. Such organic solvents cannot dissolve the inorganic coatings under discussion. Link to post Share on other sites More sharing options...
mazdaro Posted October 9, 2023 Author Share #5 Posted October 9, 2023 (edited) Yes. I tried these organic solvents, because it was mentioned in Wikipedia that MgF2 would be slightly soluble in Acetone. I certainly won't try a treatment with H2O2/NH4OH, which is the perfect means of destroying fungus in less than a minute: Mg++ cannot be oxydized and F- doesn't want. 😀 With that said, there is no need to be afraid that the oxydative removal of fungus leads to a further removal of the coating. Edited October 9, 2023 by mazdaro Link to post Share on other sites More sharing options...
Anbaric Posted October 9, 2023 Share #6 Posted October 9, 2023 I would suggest that nobody should attempt anything like this unless they are already very experienced with handling hazardous chemicals like concentrated nitric acid and NaOH, and are absolutely sure they fully understand the risks and appopriate protective measures. The patent says KOH, incidentally, which is even nastier at the same concentration than NaOH. When the HNO3 reacts with the MgF2, it will produce HF, which is very dangerous stuff. If the damaged coating is only a cosmetic defect and doesn't visibly affect image quality I would leave well alone. Link to post Share on other sites More sharing options...
mazdaro Posted October 9, 2023 Author Share #7 Posted October 9, 2023 (edited) Advertisement (gone after registration) You are surely reight. As far as I' m concerned, I have the appropriate experience. The formation of HF might be a KO criterium - for the glass. Edited October 9, 2023 by mazdaro Link to post Share on other sites More sharing options...
mazdaro Posted October 11, 2023 Author Share #8 Posted October 11, 2023 The crux of the matter is the relatively long exposure time of NaOH (The reaction between MgF2 and NaOH is purely based on thermodynamics. According to Wikipedia, Mg (OH)2 (Ksp = 5.61×10−12 ) shows an even lower Ksp than MgF2 (Ksp = 5.16⋅10−11 ) ! The formation of HF is pypassed! Fortunately, Mg(OH)2 has the great advantage that it is soluble in strong acids (F- ist a relatively weak base). Most of the MgF2(s) has already reacted to Mg(OH)2(s), when the next step will be an ultra short treatment with HNO3. In this case, the main reaction is a simple neutralisation and there is practically no formation of HF! I ordered some plastic scrabbers now and I placed the front lens in the "Voodoo mixture" Isopropanol/ Saltwater* (in order to "loosen" the layer). Let's see, whether this method works... * It was to expect that a part of the salt ions precipitated by adding Isopropanol. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/382794-how-to-remove-an-inhomogeneous-coating-mgf2-from-a-frontlens-eg-summicron/?do=findComment&comment=4873749'>More sharing options...
mazdaro Posted October 16, 2023 Author Share #9 Posted October 16, 2023 The U.S. Patent is not recommended: the glass is etched (probably by NaOH conc.)!!! The result is a dull lens! The dullness could be removed with Nigrin - that's it -, but the surface is not yet exactly flat. The lens requires further polishing. The "Voodoo" method Isopropanol/Salt-Water and plastic scraper is ridiculous (How should F- be exchanged with Cl-?) Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/382794-how-to-remove-an-inhomogeneous-coating-mgf2-from-a-frontlens-eg-summicron/?do=findComment&comment=4875983'>More sharing options...
mazdaro Posted October 17, 2023 Author Share #10 Posted October 17, 2023 To be fair, it must be said that it is very unlikely that the uneven surface structure - not the dullness! - is the result of the acid-base treatment: the base (NaOH) was approximately only 10 % at room temperature, and concentrated nitric acid can be stored in a glass bottle for a long time. The surface must have been already damaged, as can be seen in the Pic. of the Summicron. From the very beginning, Jerzy recommended https://www.optik-labor.com/ Link to post Share on other sites More sharing options...
pgk Posted October 18, 2023 Share #11 Posted October 18, 2023 19 hours ago, mazdaro said: The surface must have been already damaged, as can be seen in the Pic. of the Summicron. I've seen a few lenses with this sort of damage. Not sure of the root cause but something seems to have been able to physically or chemically alter the glass surface itself. I know that mineral glasses can be subject to 'oxidation' (chemical damage anyway) if left in contact with things like seawater for a long time, because optical ports used underwater can develop a dull 'patina' whivch has to be polished off by a specialist (usually the manufacturer). Polishing large things like ports is risky because of thermal stress as one area heats up whilst the rest remains cool - I have lost a port which shattered whilst being polished. I was made very clearl that it was at 'my risk' because of this when I got it done by the glass polisher who knew what was likely to happen, but the scratch showed in photos so it was worth trying. Link to post Share on other sites More sharing options...
mazdaro Posted November 12, 2023 Author Share #12 Posted November 12, 2023 (edited) https://www.l-camera-forum.com/topic/295398-do-it-yourself-schrauber-thread/page/74/#comments #1467 Edited November 12, 2023 by mazdaro Link to post Share on other sites More sharing options...
jaapv Posted November 12, 2023 Share #13 Posted November 12, 2023 Will van Manen told me that he prefers to use household vinegar to remove coatings. FWIIW. Link to post Share on other sites More sharing options...
mazdaro Posted November 13, 2023 Author Share #14 Posted November 13, 2023 Concentration, time? I've read about it, but didn' believe it. Link to post Share on other sites More sharing options...
250swb Posted November 13, 2023 Share #15 Posted November 13, 2023 (edited) 10 hours ago, mazdaro said: Concentration, time? I've read about it, but didn' believe it. I suppose you think a professional will give away a lifetimes experience to answer your question? Edited November 13, 2023 by 250swb Link to post Share on other sites More sharing options...
mazdaro Posted November 13, 2023 Author Share #16 Posted November 13, 2023 Perhaps Aceto Balsamico Tradizionale (12 Years Old) for 12 years.🤐 MgF2 → Mg(OAc)2 ? There is no reason why this reaction should take place. Link to post Share on other sites More sharing options...
jaapv Posted November 14, 2023 Share #17 Posted November 14, 2023 12 hours ago, 250swb said: I suppose you think a professional will give away a lifetimes experience to answer your question? Actually he. said. that he preferred rosemary vinegar for the smell 1 Link to post Share on other sites More sharing options...
mazdaro Posted November 14, 2023 Author Share #18 Posted November 14, 2023 🙂 I've recently heard that NH4OH is also possible for early Leitz coatings. Link to post Share on other sites More sharing options...
mazdaro Posted November 15, 2023 Author Share #19 Posted November 15, 2023 (edited) The lens looks good now, but it's out of focus.🙁 Unfortunately, I took no picture before polishing. That's why I can't say with certainty that the blurred pictures are a consequence of said treatment. The uneven surface, respectively, the fine scratches were by no means deep. Otherwise I wouldn't have polished the surface. In summary, I'm afraid that even professional polishing is a wasted effort. My recommendation: Don't buy such Ienses! Edited November 15, 2023 by mazdaro 1 Link to post Share on other sites More sharing options...
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