Silvering mirror - any experience?

[Michele Scotti]

I posted on the specific thread for the 800mm mirror but I guess it went unnoticed. Also I've searched for similar topic on this forum and found out only something from 2013.

Anyway - I'd like to go with Silvering (+anti-tarnishing agent). There is a big piece of work that has been done by a group in the US.  https://sites.google.com/site/spraysilveringtelescopemirrors/home

This is the quite interesting spraying process:: https://youtu.be/2noVRDWppII?t=312

I've contacted the company that sells the kit of chemicals (in the USA) -and that collaborated with the ATM team- but the very interesting price of ca. 130$ for a complete set was brutally met with a 250$ shipping cost mainly due to Hazardous Fees.

I wonder if anybody on this side of the pond have ever had some experience with that - looking for some advice.

Silver Nitrate in a pretty pure form doesn't break the bank by the look of it. 

[billhinge]

Something I wanted to try from when I  made a 8.5" mirror  in the  70's.  My concern  is about getting the chemicals (through customs). A few years ago I  bought some distilled water and acetone from local chemists. Boots  refused to  sell acetone and gave me a  hard time over distilled water! Next local chemist  made me sign the poison register for  small bottle  of acetone.   (I  know you  can get them by the gallon on ebay now). They used to have instructions  in  the old ATM vol 1 to 3

I believe you  also  need nitric acid, I'd  be worried about it getting stopped at customs but in principle it sounds cool.  I guess not many folk have tried it given its easy enough to aluminise 

Don't you have to burnish it as well? Potential downside risk sounds high in relation to  any upside benefit unless you are after the 'experience' of having done it in which case the cost shouldn't matter

 

[Astrobits]

Yes. I have silvered a few small mirrors many years ago. I am fortunate to be an industrial research chemist so had all the chemicals needed readily available. It is fairly easy to do but can go spectacularly wrong if you are not careful and don't follow the rules. There are ( if they haven't been taken down) some recipes on the web. The main hazard is that the recipes can also produce silver fulminate which is explosive and incredibly sensitive and can detonate by itself (so no good for the usual uses of explosives). The ATM books have instructions and recipes and Stellafane.org has a page with some links.

Nigel

[fozzybear]

you could try these guys

https://www.kingsviewoptical.com/precision-optics-services/optical-vacuum-coating-uk/

[tomato]

Personally, in this day and age, I wouldn’t attempt this. You will probably get added to some terrorist watch list when you try to source the chemicals.

Also, based on my 42 years of experience working in the chemical industry, you don’t want to be handling nitric acid in your shed.

[johninderby]

An interesting read on handling nitric acid. Not something for amateurs.. 🙀🙀🙀

https://www.ehs.washington.edu/about/latest-news/nitric-acid-incidents-how-reduce-your-risk

Edited June 28, 2021 by johninderby

[Michele Scotti]

14 hours ago, fozzybear said:

you could try these guys

https://www.kingsviewoptical.com/precision-optics-services/optical-vacuum-coating-uk/

I'm talking about Silvering -as an alternative to Aluminizing-. Specifically spraying Silvering

1 hour ago, johninderby said:

An interesting read on handling nitric acid. Not something for amateurs.. 🙀🙀🙀

https://www.ehs.washington.edu/about/latest-news/nitric-acid-incidents-how-reduce-your-risk

Can't see the use of Nitric Acid in this process

[Michele Scotti]

22 hours ago, Astrobits said:

Yes. I have silvered a few small mirrors many years ago. I am fortunate to be an industrial research chemist so had all the chemicals needed readily available. It is fairly easy to do but can go spectacularly wrong if you are not careful and don't follow the rules. There are ( if they haven't been taken down) some recipes on the web. The main hazard is that the recipes can also produce silver fulminate which is explosive and incredibly sensitive and can detonate by itself (so no good for the usual uses of explosives). The ATM books have instructions and recipes and Stellafane.org has a page with some links.

Nigel

Hi Nigel, is the process you're familiar with an 'immersion' type?

Also, out of curiosity, where the fulminate can generate from?

Btw, I need to fetch the list of chemicals involved in this process and post it here

[Astrobits]

Yes, immersion procedure. This was way back in the late 60's/early 70's and spray silvering hadn't been developed. I don't remember using Nitric acid in the procedure and don't think it is necessary. I suspect that it was used as it was readily available then ( as a teenager I used to buy concentrated acids, Sulphuric, Nitric and Hydrochloric, from my local chemists!!! ).

The Fulminate normally appears when the mixed solutions are left standing for a period of time. I'm not sure of the exact chemical reactions that generate it. See this link: 

https://www.compoundchem.com/2017/09/06/silver-mirror/

Nigel

 

[Michele Scotti]

3 hours ago, Astrobits said:

Yes, immersion procedure. This was way back in the late 60's/early 70's and spray silvering hadn't been developed. I don't remember using Nitric acid in the procedure and don't think it is necessary. I suspect that it was used as it was readily available then ( as a teenager I used to buy concentrated acids, Sulphuric, Nitric and Hydrochloric, from my local chemists!!! ).

The Fulminate normally appears when the mixed solutions are left standing for a period of time. I'm not sure of the exact chemical reactions that generate it. See this link: 

https://www.compoundchem.com/2017/09/06/silver-mirror/

Nigel

 

Interestingly silver spraying is avaialbe as a kit in the US (https://angelgilding.com/silver-on-glass/spray-silver.html) and a collaboration started with some ATMs - I'd say they're almost done in proving the enhanced durability of the process + antiaging agent.

My understanding is that this is modern approach to Silvering where:

• there is no hazard
• it's "easy" for ATMs
• durability is similar to Aluminium - or at least not as bad as 1y refresh needed-
• it's in general cheaper than Aluminium - at least for my personal project

Would you be able to have a look at the chemical kit? I've got the info below from the data sheets from Angel Gild website.

As far as I get it: preparation with "Tin for Silver Concentrate", spraying simultaneously "Sensitizer for 2-Part Silver Solution" + "2-Part Spray Silver Reducer"

Tin for Silver Concentrate
SnCl2·2H2O
Stannous chloride dihydrate
1 - 5 Weight %

2-Part Spray Silver Solution
Silver nitrate  AgNO3
10 - 25 weight-%
Ammonium hydroxide (Ammonia solution 25%) NH4OH 
5 - 10 weight-%

2-Part Spray Silver Reducer – C3030
Sodium hydroxide 
10 - 25 weight-%
Ammonium hydroxide 1336-21-6 
1 - 3 weight-%

*The exact percentage (concentration) of composition has been withheld as a trade secret.

 

[Astrobits]

I saw that Angel Guilding article in Sky & Telescope January 2020 and have considered doing it with my mirrors ( when I get round to making them, or my current scope needs re-coating). I don't know if the spray bottles are available here or will need to be obtained from the States. The raw chemicals are common and should be available fairly easily although I have not tried to purchase any yet but should be cheap enough to do some experimental silvering to get the desired effect.

Nigel

[Michele Scotti]

19 minutes ago, Astrobits said:

I saw that Angel Guilding article in Sky & Telescope January 2020 and have considered doing it with my mirrors ( when I get round to making them, or my current scope needs re-coating). I don't know if the spray bottles are available here or will need to be obtained from the States. The raw chemicals are common and should be available fairly easily although I have not tried to purchase any yet but should be cheap enough to do some experimental silvering to get the desired effect.

Nigel

Well, I've enquired them directly - the bundle incl. antiaging is ca. 130USD......shipment to Italy (where the mirror is) is ca. 250USD which I find outtrageously high although it's dirven by 'hazardous material fee'

As a consequence I'm trying to figure out the process to reproduce it. I'm not a chemist so I can't figure out the % of the mixed involved which are kept vague in the datasheet as "trade secret".

Other 2 reasons why I'm very interested in silvering:

- no shipment concerns/risks

- over 500mm I understand it's increasingly more difficult to find places that can Aluminize 

[Gasman]

Have you tried local universities?  A nice chat with the lab tech at my local uni got my 8inch home ground mirror aluminised many moons ago , if I recall it could have been coated in whatever I wanted even gold 😁. Just cost me a nice bottle of single malt!

Steve

[Zermelo]

"Chemical Curiosities" by Roesky and Mockel has a procedure that uses silver nitrate, hydrazinium sulphate and aqueous ammonia. They also reproduce a rather more involved technique recorded by Liebig in the nineteenth century.

I'm sure I remember reading a method that calls for nitric acid but I can't lay hands on it. Nitric acid could be a bit of a red flag as it's used in preparing some rather undesirable stuff (some U.S. states are especially touchy). The fuming strength acid is more dangerous, and probably impossible to obtain; diluted solutions are sometimes available online. It can be prepared relatively easily, but it's another one of that (increasingly large) set of experiments that once used to be carried out by schoolboys in shorts, but these days is deemed best avoided.

[Astrobits]

On their "How to" video they use multiple coats if necessary. Therefore I would go for the low concentrations and expect to need to do multiple passes to get the thickness. However, you will need accurate scales to measure gram amounts.

I don't see the kit for $130. The two spray bottles and wand nozzles alone are priced at $208?

Nigel

[Michele Scotti]

11 hours ago, Astrobits said:

On their "How to" video they use multiple coats if necessary. Therefore I would go for the low concentrations and expect to need to do multiple passes to get the thickness. However, you will need accurate scales to measure gram amounts.

I don't see the kit for $130. The two spray bottles and wand nozzles alone are priced at $208?

Nigel

This is what you need:  https://angelgilding.com/2-part-spray-silver-concentrate.html

+ "Tin for Silvering" . The antiging is another 15USD.

I would not buy bottles and nozzles that I can easily buy here.

The ATM group is applying one coating - they've published some study in terms of reflectivity too

[Astrobits]

Your post mentioned "the bundle" and I assumed that you were referring to the whole kit and not just the chemicals. When (if) you purchase the chemicals you will have far more than needed for one mirror so you will be able to experiment on window glass to get the concentrations for one coat. My suggestion of starting with the lowest concentrations was simply to minimise the waste incurred in any trials that fail. Clearly, the American ATM's are using the product as supplied by Angel Guilding who have done these trials and determined the best concentrations for one coat. By starting with the lowest concentrations you will be able to get an idea of the concentrations that should provide a one coat solution. If you need to spray twice then doubling up the concentration should get you near there, if you need three coats then three times as much etc.

I'm interested in what equipment you choose for this project as I might want to go the same route.

Nigel

[Michele Scotti]

20 hours ago, Gasman said:

Have you tried local universities?  A nice chat with the lab tech at my local uni got my 8inch home ground mirror aluminised many moons ago , if I recall it could have been coated in whatever I wanted even gold 😁. Just cost me a nice bottle of single malt!

Steve

I have an 800mm piece of glass - it's a bit out of the std research equipment.

Also, I really think it's time to reconsider Silvering - I remember the first time I've heard of it and I was like 'nah, that's old stuff'....not anymore apparently

[Michele Scotti]

4 hours ago, Astrobits said:

Your post mentioned "the bundle" and I assumed that you were referring to the whole kit and not just the chemicals. When (if) you purchase the chemicals you will have far more than needed for one mirror so you will be able to experiment on window glass to get the concentrations for one coat. My suggestion of starting with the lowest concentrations was simply to minimise the waste incurred in any trials that fail. Clearly, the American ATM's are using the product as supplied by Angel Guilding who have done these trials and determined the best concentrations for one coat. By starting with the lowest concentrations you will be able to get an idea of the concentrations that should provide a one coat solution. If you need to spray twice then doubling up the concentration should get you near there, if you need three coats then three times as much etc.

I'm interested in what equipment you choose for this project as I might want to go the same route.

Nigel

I'm not really keen to spend 250USD on shipment -there is something being 2x the value of the material that goes against my ethos.

I've opened this thread to figure out a way to do that here in Europe.

Btw I don't think they go down the 'Tollen's reagent' route - as the previous link you kindly shared. My understanding is that is good for a second surface mirror because the 'sugar' leave a residual which is unwanted for a first-surface astronomical mirror.

Here below the 'equipment' I have in mind: £5 spray bottles + gloves + tilting jig.

[Gasman]

3 hours ago, Michele Scotti said:

I have an 800mm piece of glass - it's a bit out of the std research equipment.

Also, I really think it's time to reconsider Silvering - I remember the first time I've heard of it and I was like 'nah, that's old stuff'....not anymore apparently

Ah right I think 800mm might be a bit too big for yer average lab 😳

[Astrobits]

I will be interested in using two separate bottles, one for each hand. I can foresee that the two hands approach might give some variation in quantity of material dispensed and possible inhomogeneity to the coating but worthwhile to try that. Certainly the cheapest way.  

The recipe in ATM book 2 includes glucose and silvers the mirror suspended face down in the final mix ( obviously not practical for 800mm mirrors ). Also the Material Safety Data Sheet ( MSDS ) for the Angelguilding reducing mix ( buried on p9 ) shows that it contains an unidentified ingredient which may well be glucose or something to do the same job:

 

 Nigel

[Michele Scotti]

6 hours ago, Astrobits said:

I will be interested in using two separate bottles, one for each hand. I can foresee that the two hands approach might give some variation in quantity of material dispensed and possible inhomogeneity to the coating but worthwhile to try that. Certainly the cheapest way.  

The recipe in ATM book 2 includes glucose and silvers the mirror suspended face down in the final mix ( obviously not practical for 800mm mirrors ). Also the Material Safety Data Sheet ( MSDS ) for the Angelguilding reducing mix ( buried on p9 ) shows that it contains an unidentified ingredient which may well be glucose or something to do the same job:

 

 Nigel

Good catch Nigel - I'm kind of surprised that there's nothing available in Europe - a real pity.

About the spraying consistency - interestingly enough the procedure calls for try out on a some measuring cup to adjust the nozzles. I guess one needs to practice a bit - pumping those things takes some stamina 

[Astrobits]

In my experience those simple hand trigger sprayers in your post have very variable sprays which are NOT adjustable other than by varying the finger pressure applied to the trigger. I have looked on the web for ones similar to those sold by Angelguilding ( which I assume have got adjustable nozzles ) and have so far come up blank. This is not to say that the simple sprayers won't work, They are cheap enough to try them, it might be necessary to purchase more than two to select the best pair.

Nigel

[The Admiral]

I've never tried it, and I don't know if this is of any interest, but there is a short chapter in a book called 'Constructing and Astronomical Telescope'. It was first published in 1947, but this is from a second edition from 1955. 'Elf & Safety' of course is nowhere in line with what we have today! It is an immersion process.

Silvering.pdf

Ian

Edited July 1, 2021 by The Admiral