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[*] posted on 29-8-2015 at 13:59
Silvering Failures and Waste Disposal


Following the nurdrage Silvering mirror thing thrice, i've had no joy at all.

The process is 1g AgNO3 dissolved in water, add 1g NaOH dissolved in water, mix, re-dissolve the precipitate in NH3 solution then add 4g Sucrose solution, heat, wait.

I'm now at a loss as to what to do with the Waste products.

Chucking on the land sounds like a Bad idea, and bottling it and throwing in the bin would end up being the same thing.

Any suggestions ?




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[*] posted on 29-8-2015 at 14:09


Did it work at least ?

Last time I did this, I only reserved the waste solution in a bottle, telling me that the colloidal silver could be useful (if I ever had the chance to filter it).
If you're sure that every bit of Silver Nitrate has reacted, maybe you could filter it and get the silver back (if you've got the right sintered glass funnel)
Also, if you aren't sure that all the silver as reacted, you might want to add something to make it precipitate (lot of silver salt are insoluble), which could again be filtered.

Edit: Read again, it obviously didn't worked as planned :(

[Edited on 29-8-2015 by Firmware21]
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[*] posted on 29-8-2015 at 14:31


It did NOT work three times.

Recovering the silver metal isn't important.

I would just like to make it safe to dispose of and forget the whole thing.

It was a Boast that i could Silver the inside of an empty wine bottle having seen a couple of youtube videos and having the reagents.

Uber Fail.

Some people never Learn from their mistakes and i'm one of them.




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[*] posted on 29-8-2015 at 14:51


Then, I'd suggest you to neutralize the solution with an acid (I'm thinking of nitric acid for this purpose), it would bring all the Ammonia to ammonium nitrate and you'd be left with a mixture of Ammonium nitrate, sugar acids and silver particles solution. That would be a good start.
Maybe boilling it down (after neutralizing) ?

It's also wierd that you didn't get any significant result, it always worked for me so far.

[Edited on 29-8-2015 by Firmware21]
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[*] posted on 29-8-2015 at 15:03


Could you please post the exact process that you did Firmware21 ?



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[*] posted on 29-8-2015 at 15:19


It went like this:

I prepared ~1 gram of AgNO3 in an erlenmeyer, which was then dissolved in 30 ml of deionised water. I then added about 3 to 6 ml of concentrated ammonia, which upon addition made an interesting yellowish precipitate that quickly dissolved. I then prepared a solution of glucose (the advantage of helping a friend in a school project), something like concentrated, must have added at least 1.5 grams in 30 ml deionised water, might be more since we only had a 50 years old balance and couldn't weigh out properly.
At last, I mixed the two solutions, added an old but clean microscope "glass slice" and stoppered. At first nothing happened, but upon heating, the solution became yellowish and suddenly turned black. I shaked the the vessel like an ape for 5 minutes.

It gave pretty nice results. Maybe a clean, scratched glass surface would help the silver to settle.

Edit: I can't even read my old protocols, it must be fixed now. (I hope)

[Edited on 29-8-2015 by Firmware21]
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[*] posted on 29-8-2015 at 15:29


Thankyou.

Glucose.

I'll split some by hydrolysis from household sucrose with potassium bitartate and heat (115 C), separate it from the Fructose and see if that works better.




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[*] posted on 29-8-2015 at 15:49


Maybe I found a better "recipe" for this reaction. It's from my old highschool lab book.

"1. Clean thoroughly the piece of glass with a bit of alcohol, and then with acetone.
2. Take a 250 ml beaker and add 20 ml of a 5% AgNO3 solution.
3. Add 1/2 teaspoon of glucose.
4. Dip the piece of glass in the solution and stir the solution with a magnetic stirbar.
5. while stirring, gently heat the mixture for about 3 minutes until the solution turns brown-gray
6. While stirring, further heat the beaker for about 10 to 12 minutes, make sure NOT to boil the mixture.
7. When the reaction stops. The exceding Silver should be floating on top of the solution. The piece of glass should be covered with a thin layer of silver.
(optional)
To protect the layer from degradation, one could rince the piece of glass twice with ethanol and then twice with Hexane. prepare a dilute solution of lacquer, apply it to the whole surface and let it dry. " Translated from french.

It might be a little more precise than my version (which I must admit was pretty much make do)

[Edited on 29-8-2015 by Firmware21]
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[*] posted on 29-8-2015 at 19:14


Quote: Originally posted by aga  
I'll split some by hydrolysis from household sucrose with potassium bitartate and heat (115 C), separate it from the Fructose and see if that works better.

I bet it will. One of the things I learnt at school is that Sucrose does not work in this experiment, one has to use a so-called "reducing sugar" to reduce the Ag(I) to Ag(0).
All monosaccharides are reducing sugars, because their ring-shaped structure can actually open out into one long string with an aldehyde group at the end. This aldehyde group is the bit that does the actual reducing and disaccharides (e.g. Fructose) don't have this group because it got used up when the two monosaccharides joined together.

I would suggest just adding a dash of dilute HNO3 or similar to a solution of sucrose and heating for a bit to hydrolyse the sucrose back into glucose and fructose and just using that mixture as-is in your experiment. No need to separate the glucose from the fructose, they will both work equally well for this experiment. Please note however that you shouldn't use HCl or H2SO4 for this as of course Ag2SO4 and AgCl are insoluble.
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[*] posted on 29-8-2015 at 20:42


I've attached a file, which is a segment I copied out of an old book on how to silver telescope mirrors. I've used Brashear's method a number of times to silver the inside of jelly jars and such things, and I've made a series of mirrors and framed them, including one large enough that my daughter uses it regularly. I did it just for fun.

After I was done I acidified the silvering solution (which contains an ammonia complex) with hydrochloric acid, which renders it safe (otherwise there is danger of forming explosive compounds after an hour or two), and which coincidentally precipitates all the silver as the chloride. I filtered this off, and poured the rest down the drain. Later I used another procedure to recover the silver from the chloride.

Nurd Rage's video made it look a lot simpler than Brashear's method, which takes some effort and can be tricky. However as I recall Nurdrage's mirror didn't come out perfectly, and I've had very good results.

I followed the instructions in cleaning my glass before silvering----that meant, first, dish soap, rinse in distilled water; then acetone, and more distilled water rinse; finally scrub with nitric acid, and more distilled water rinse. I found I could use two glass rods as chopsticks, with cotton balls dipped in nitric acid. It worked better than trying to do with butyl gloves.

Attachment: silver2 (16kB)
This file has been downloaded 422 times





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[*] posted on 29-8-2015 at 21:35


The file on telescope silvering is from J. B. Sidwick's "Amateur Astronomer's Handbook", the third edition I believe.

Brashear's method is the most commonly used for telescope mirror silvering (it is a convenient way of putting a newly made mirror into use without sending it off to a evaporative coating lab). I have participated in the successful silvering of a telescope mirror using this technique.

For maximum durability the glass is first treated with a tin(II) chloride solution before silvering (helps with the silver adhesion), and is treated after silvering with benzotriazole.
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[*] posted on 30-8-2015 at 00:37


Thanks for all the info peeps.

Will try it again.




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[*] posted on 30-8-2015 at 03:52


Quote: Originally posted by Firmware21  
Then, I'd suggest you to neutralize the solution with an acid (I'm thinking of nitric acid for this purpose), it would bring all the Ammonia to ammonium nitrate and you'd be left with a mixture of Ammonium nitrate, sugar acids and silver particles solution. That would be a good start.
Maybe boilling it down (after neutralizing) ?

It's also wierd that you didn't get any significant result, it always worked for me so far.

[Edited on 29-8-2015 by Firmware21]


I'm thinking that adding acid is a good idea, but adding nitric acid isn't.
Adding HCl will precipitate the dissolved silver as the chloride.
Filter off the AgCl and any Ag that's present, rinse it and heat it red hot with washing soda to get silver, (partly because it's nice to have little lumps of silver, but mainly because silver compounds are a bit environmentally unfriendly).
Adding nitric acid to sugar and boiling it down isn't a good idea- at best you risk generating lots of NOx fumes and, if you are really unlucky, you get en explosion to go with them.
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[*] posted on 30-8-2015 at 05:47


You must use a reducing sugar like glucose. Sucrose is non-reducing and stable to hydrolysis (inversion) at alkaline pH.

Just add a drop of acid to your sucrose solution (avoid HCl for the Cl-, and HNO3 will hydrolize and give -onic/-aric acids) and boil for a short while. You should get equimolar glucose + fructose. While not technically a reducing sugar, fructose rapidly isomerizes to glucose + mannose under alkaline conditions. Hopefully, the acid you used was in a small enough quantity so as not to appreciably ppt your Ag+ (the sulfate salt is soluble up to about 8.3 g/L).

Also, you can heat it up a little bit...or, "shake it like an ape".

O3




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[*] posted on 30-8-2015 at 08:20


Quote: Originally posted by Ozone  
You must use a reducing sugar like glucose. Sucrose is non-reducing and stable to hydrolysis (inversion) at alkaline pH.

Just add a drop of acid to your sucrose solution (avoid HCl for the Cl-, and HNO3 will hydrolize and give -onic/-aric acids) and boil for a short while. You should get equimolar glucose + fructose. While not technically a reducing sugar, fructose rapidly isomerizes to glucose + mannose under alkaline conditions. Hopefully, the acid you used was in a small enough quantity so as not to appreciably ppt your Ag+ (the sulfate salt is soluble up to about 8.3 g/L).

Also, you can heat it up a little bit...or, "shake it like an ape".

O3


The original procedures for telescope mirror silvering included the acid hydrolysis of sucrose as part of their preparation, a procedure abandoned in favor of using pure glucose due to inconsistent results. Of course, if you are just doing a silver demo you probably don't care too much about film quality.

The Sidgwick file posted above has a specific recipe for sucrose based reducing solution:
"A third reducer, which employs ordinary table sugar but may be used
immediately, is as follows: Table sugar 100gr; Nitric acid (conc) 40
cc; distilled water to 1000cc. Bring to the boil, and allow to cool
before using. If it is to be stored, add 175cc alcohol."

Silvering was invented by Liebig, and turned into a process suitable for telescope mirrors by Steinheil and Foucault.

[Edited on 30-8-2015 by careysub]
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[*] posted on 30-8-2015 at 08:39


Brauer uses sugar too. Technique. Details. Standing for a week with alcohol and not much acid. Brauer also recovers silver with HCl but reduces the chloride with zinc. The balance has implied that the hot chloride reduction doesn't work as well for me as it has for others.



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[*] posted on 30-8-2015 at 10:29


Well, i tried it again, using a 'script' for a demonstration, imagining that something written for demonstration should work every time.

http://ocw.mit.edu/high-school/chemistry/demonstrations/vide...

I was Wrong again. Didn't work despite fifteen minutes shaking.

(lucky that males can make a repeated vigorous up and down motion using one hand for long periods of time).

I'm thinking that either my glass is not clean enough, or the glucose was candle wax with an identity crisis.

Clearly all the processes referenced can work, so i'm definitely doing something wrong.

Maybe try the sugar to invert thing with nitric tomorrow.




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[*] posted on 30-8-2015 at 11:01


I have only ever got the silver mirror test to work with bran new unused test tubes. It seems that anything other than a perfectly clean glass surface fails.

How did you clean the glass?
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[*] posted on 30-8-2015 at 11:06


I opened the bottle, then waited about 3 beers (roughly an hour) until all the wine disappeared, washed it a bit, then used it.

So all the wash in Nitric, scrub clean, scrub again, rinse in acetone etc is necessary ?




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[*] posted on 30-8-2015 at 11:18


If you are going to use nitric (obviously for the advantage of not having a ppt'ing counter-ion), don't use much. Otherwise, you will oxidize at least some of your reducing sugars to the -onic and then -aric acids.

Nitric is routinely employed for the preparation of glucaric acid from glucose/sucrose...in stoichiometric quantities, mind, so maybe 2-3% won't be so bad (for a demo, anyway)?

O3




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[*] posted on 30-8-2015 at 12:33


Unrelated, but a Sig change due to Amos coming up with a Much better one.



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[*] posted on 30-8-2015 at 12:56


Telescope mirror coaters are of course typically applying the silver to a perfectly clean virgin glass surface that has just finished polishing to a final optically smooth surface. Can't do better than that.

Some mirrors are being recoated and will have been stripped with ferric chloride solution, which apparently leaves a good surface for slivering (although other the metal film that was stripped off the glass was still quite clean).

You might try cleaning with ferric chloride, and then treating with tin chloride, the same surface treatment sequence used to prepare mirrors.
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[*] posted on 1-9-2015 at 20:07


careysub---I appreciate your expertise in this subject. You must have been an amateur astronomer. As I recall silver has better reflectivity than aluminum, especially at high frequencies, but aluminum lasts longer and resilvering your mirror every year is a pain so everyone uses aluminum now.
Silver at least has the advantage that it can be done at home.

When I was doing my work I just bought some glucose. Before doing that I hadn't known that glucose and dextrose are the same thing. I had good results in silvering a variety of objects, the largest was a flat piece of glass, 12 x 16 inches. I put that in a nice frame and now my daughter uses it in her bedroom. I just used window glass from the hardware store, but I was paranoid about cleaning it, as the excerpt from the book says to do. I didn't have a nice silvering tray of the right size (13 x 17 inches would be about right), so I made a shallow box out of wood and then coated it in paraffin. It worked fine, and the paraffin stands up to nitric acid etc. I coated the silver side of my mirror with several layers of polyurethane, hopefully to protect it from the atmosphere for a long time. It's been a couple of years and so far the silver is still bright.

I'll take a picture of some of my silvering work and post it. BTW I didn't put any tin on the mirror before silvering.




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[*] posted on 10-9-2015 at 11:39


The best silver mirrors I have made are those produced by cleaning the glass with concentrated nitric acid. 28% ammonia solution works almost as well to prepare the glass surface. No need to scrub or anything, just a few seconds of sloshing one of those around in the vessel and rinsing with distilled water afterwards does the trick.



Note to self: Tare the damned flask.
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[*] posted on 10-9-2015 at 11:46


Cheers for the advice Mimp.

I suspect that either the reagents or the operator are to blame in my case.

4 failed attempts so far, with reactants left overnight to see if the bottle would at least explode.

Nothing.

No silvering. No explosions. Just Ag crud to reprocess.

[Edited on 10-9-2015 by aga]




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