Re: [ATM] Silvering Woes

["Bill Kelley" <flex@commspeed.net>]

Donald,

You didn't mention preparing and adding a reducing solution ??

I use a Peacock kit for silvering mirrors for my students. Works fine.

Bill Kelley

----- Original Message ----- 
From: "Donald R. Bates" <dbates3@houston.rr.com>
To: <atm@atmlist.net>
Sent: Thursday, December 29, 2005 4:57 PM
Subject: [ATM] Silvering Woes


> After finishing the figuring of a 6-inch  mirror recently, I decided to 
> try
> my luck with coating it with silver myself. I researched the process, and
> found a good recipe from Michael J. Coslo that was posted to ATM Archive
> site back in the late 1990's. After some searching, I found a local 
> chemical
> supply shop that had everything I needed to get started. I was amazed how
> easy it was to obtain things like Nitric Acid, Silver Nitrate, etc. With 
> my
> lab assistant, (my father, a retired chemical engineer) I carefully 
> followed
> the directions. When I pulled the mirror from the silvering bath, it was
> still completely transparent, no silver had attached itself to the face of
> the mirror.
>
> Undaunted, I cleaned the mirror with Nitric Acid, and tried again the next
> day. This time, all the predicated color changes in the solution occured
> exactly as described. Once again, I agitated the mirror face down in the
> silvering solution, and pulled it from the bath. Again, no silver clung to
> the mirror! After wasting two batches of Silver Nitrate, I gave up and 
> sent
> the mirror off for aluminizing. Does anyone out there know what I might 
> have
> done wrong? I have eliminated what I think re the most likely culprits:
>
> Temperature - The "Lab" temperature was perfect, around 65 degrees; same
> with the chemical solutions.
>
> Surface of mirror not clean enough - I scrubbed the surface with so much
> Nitric, that it was super-clean.
>
> Too much Ammonium Hydroxide - I was very careful not to add to much AH, 
> and
> even added a few more drops of Silver Nitrate for good measure.
>
>
>
> A few other considerations:
>
> - No silver attached to the tray container either. Just a grey sludge at 
> the
> bottom.
>
> - The only thing I did different from the instructions was to put a 
> suction
> cup on the back of the mirror, and put it face DOWN in the solution. The
> mirror had a few chips in the outer edges that prevented a good seal for a
> face-up dam. I have also read that face down produces a better quality
> coating.
>
>
>
> I have included the exact directions that I followed below. I would still
> like to give this a try, but I need some help on where I may have gone
> wrong. It would be really great to be able to coat my mirrors without send
> them off to the aluminizer. Plus, I love playing the part of the mad
> scientist! Thanks!
>
> Donald R. Bates
>
> Chief Observation Officer
>
> Cypress Creek Station (My backyard)
>
>
>
>
>
>
>
> Telescope Mirror Silvering Method
>
>
>
> Chemistry needed:
>
> Silver nitrate, .75 ounce
>
> Ammonium Hydroxide .90 specific gravity aqueous solution 250 ml
>
> Potassium Hydroxide pellets .5 ounce
>
> Distilled water - 1 gallon
>
> 2 ounces sucrose
>
> Citric acid
>
>
>
> Cleaning mirror:
>
> Dishwashing detergent
>
> Acetone
>
> Concentrated Nitric Acid
>
>
>
> Labware:
>
> Stirring rods
>
> Rubber gloves
>
> Tray for mirror
>
> Absorbent cotton. Get the good stuff, it has longer
>
> fibers of cotton that won't be coming off on the mirror.
>
> Beakers and bottles for various solutions. The largest you need
>
> is 1 liter.
>
> 2 Eyedroppers
>
> Popsicle sticks (unused of course)
>
> Eye protection
>
> Cellophane type tape, two or three inches wide, for tape dam
>
> 2.5 or 5 gallon plastic bucket
>
> Mixing Silvering chemistry:
>
>
>
> Silver Nitrate solution:
>
> 21 grams Silver Nitrate dissolved in 250 ml distilled water
>
> Ammonium hydroxide solution -- .90 specific gravity (other s.g's will 
> work)
>
> around 100 ml
>
> Potassium Hydroxide solution:
>
> 15 grams Potassium Hydroxide pellets dissolved in 250 ml distilled
>
> water
>
> Invert sugar solution:
>
> Dissolve 60 grams sucrose in 500 ml distilled water
>
> add 10 grams citric acid.
>
> Bring to slow boil for 30 minutes (remember a slow boil, we don't
>
> want to make candy here). The volume will decrease by approximately half.
>
> Remove from heat and let cool to room temperature.
>
>
>
> After the chemistry is made and is stabilizing to room temperature,
>
> you can now start cleaning the mirror. All the steps should be sequential,
>
> and the mirror should not dry after the nitric acid steps.
>
>
>
> Cleaning Mirror:
>
>
>
> 1. Wash the mirror with detergent solution at room temperature.
>
> Rinse completely.
>
> 2. You now will swab the concentrated Nitric acid onto the mirror. Keep 
> the
> acid on the top of
>
> the mirror only, you want to keep the sides dry so you can put the dam
>
> around the mirror. You don't need to use great amounts of acid, just wet
>
> the swab and swirl around, getting all the surface of the mirror.
>
> 3. Use another swab to remove the Nitric acid from the mirror.
>
> Leave the surface of the mirror wet.
>
> 4. Repeat steps 6 and 7 at least three times.
>
> 5. Place a tape dam around the circumfrence of your mirror. Get
>
> this part done without letting the surface of the mirror dry. Plan on
>
> around an inch over.hang above the mirror surface. If at this time you see
>
> any beading of water on the mirror, hang your head in shame. It means you
>
> didn't clean the mirror properly, and you have to start over again. If you
>
> followed the instructions carefully, your mirror should be quite clean.
>
> 6. After the dam is in place, pour distilled water into the dam to
>
> cover and protect the clean surface. The mirror is now chemically clean 
> and
>
> grease free
>
>
>
> Preparation of the silvering solution:
>
> 1. In a 1 liter beaker, pour 225 ml of the Silver Nitrate solution.
>
> Reserve the other 25 ml of solution for later addition.
>
> 2. With the eyedropper, add Ammonium hydroxide to the main
>
> solution. The Silver Nitrate solution will turn a brown color. Stir
>
> constantly, adding the Ammonium hydroxide a few drops at a time. The
>
> solution will start to clear after a bit. You will see the solution
>
> clearing in the region of AH addition as you drop it in. This will give 
> you
>
> some idea of what the clearing looks like. Don't rush this part. You don't
>
> want too much AH in the solution.
>
> 3. After the solution has cleared, add a few drops of silver
>
> nitrate solution, using a different dropper. Adjust the solution until it
>
> is just a little bit cloudy.
>
> 4. Add all the Potassium Hydroxide very slowly, and with stirring
>
> to the main solution. If a giant dollop of Potassium hydroxide solution is
>
> added very quickly, other chemicals can form, which are not safe, and will
>
> destroy the operation. This won't likely happen if added slowly. The
>
> solution will turn brown again.
>
> 5. Add AH solution again, using the eyedropper, to clear the
>
> solution. Work very carefully, as we don't want too much AH in the
>
> solution. When the solution clears, it will likely be a light brownish
>
> color, and may have little black specks in it.
>
> 6. Add more of the reserve Silver nitrate solution to the main
>
> solution, a few drops to be sure that there isn't an excess of AH.
>
> The next parts happen pretty fast, so you may want to rehearse a
>
> few times before mixing any chemicals before trying it with the chemistry.
>
> 7. Pour the invert sugar into the main solution with stirring. The
>
> solution will change to a different color of brown.
>
> 8. Pour the distilled water out of the mirror dam. The plastic
>
> bucket will suffice for this.
>
> 9. Pour the main solution onto the mirror surface. The solution
>
> will continue to change in appearance. All the appearances will be pretty
>
> ugly. You'll wonder how anything shiny can come out of something that 
> looks
>
> so much like sewage.
>
> 10. Agitate the solution on the mirror fairly often. Constantly is
>
> okay, but don't overdo it and send the solution over the sides of the dam.
>
> 11. This process will continue for about 8 to 10 minutes.
>
> 12. The solution will now be a really ugly brown-black with a lot
>
> of sludge at the bottom. Pick up the mirror and pour the solution out and
>
> rinse with plenty of room temp. water. Be sure to get the main portion of
>
> the gunk off quickly. Then work your away around the mirror more 
> leisurely.
>
> Beware, as the wet silver coating is fragile. I would not even wipe it off
>
> at all. Cut the tape dam off, being careful to not let the tape come into
>
> contact with the mirror surface.
>
> 13. Before the mirror drys, place it at an angle against a support
>
> in a tray or in the sink, and rinse it off with distilled water so that no
>
> water spots are left on the mirror surface after drying.
>
> 14. Stand back and admire.
>
>
>
>
>
>
>
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> 


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