Silver plating

[diemkae]

Discussion of some methods suitable for home use

[Jerry]

There are several methods of silver plating, chemical and PVD. Depends on what you want to coat, glass, metal, whatever.

And do you want to coat specifically silver (Ag) or do you want a silver reflective coating?

[diemkae]

In spite of some "experts" on the net who assert that no one has
discovered a way to silver plate (electro or otherwise) using AgNO3,
this method works rather well to restore worn or damaged silver
plated flatware.

Here's the current (no pun intended) set up:

MATERIALS:

- stainless wand, flattened at one end

- cotton balls

- 1.5v AA cell with leads & alligator clips

- 0.6 M AgNO3 solution, e.g. 0.5 g AgNO3 + 5 ml distilled water

- Caswell "Silverplater" polish & silver plating cleaner

- "SoftScrub" cleaning product, or home-made equivalent (see
"WHERE TO GET ..." below).

- Wright's Silver Cream

Note that CLEANING is the most important step because if you don't
do that right, you're just wasting your time and materials! As for
cleaning, about 3/4 thru the Caswell Silver brush plating video

http://www.youtube.com/watch?feature=pl ... oOULQYb58E
they demonstrate how to clean a piece of Cu using several vigorous
scrubs with "SoftScrub" until water no longer beads on the surface.
They call this the "Waterbreak Test".

CREDIT WHERE CREDIT IS DUE:

The electro-plating method here is based on my extrapolations from the
Caswell video above, Strong's "Procedures in Experimental Physics",
combined with some "intuitive remains" of long-ago college chemistry.

THE PROCESS:

Original contition

A - PREPARATION:

1 - with a dremel tool, use a small (1/8" x 1/2" diameter) hard felt
wheel & tripoli to eliminate as much pitting as possible without making
a "dent", and feather the edges of the Ag to base-metal boundary

after tripoli polish

2 - use a large (4" diameter) soft buffing wheel & tripoli to buff
the general area

3 - wash in hot water + detergent; both the base metal and the
surrounding silver plate should have a high polish

B - CLEANING:

To restore worn spots on silver-plated flatware & other small areas
of base metal that have been brought to a high polish with tripoli &
rouge, I have found that, for my purposes, it is sufficient to just wash
with detergent, scrub once with the likes of "SoftScrub", then go to
step 1 under "PLATING", below.

While this cleaning method works well on small areas, plating a large
flat area is likely to require more thorough cleaning!

C - PLATING:

1 - rub briskly for 30 seconds with a cotton ball wet with a drop or
two of (well shaken) Caswell's "Silverplater". This will put down a
thin layer of silver sufficient to make the (bronze) color of the base
metal almost indistinguishable from the surrounding silver plate.

Wipe the workpiece with a damp paper towel to remove any
Silverplater residue, to avoid contaminating the AgNO3 solution on
the wand and the AgNO3 solution. Contamination is evidenced
by an ammonia smell on the wand and cloudiness/precipitate in
the AgNO3 solution (see "update for chemistry geeks", below).

2 - to increase the thickness of the Ag layer, attach battery (-)
to workpiece (cathode), and the battery (+) to the stainless wand
(anode) the flattened end wrapped with 1/2 a cotton ball & thoroughly
wet with the 0.6 M AgNO3 solution and slowly, but firmly, rub the
prepared area in a circular pattern or brush-strokes for about 60 to
90 seconds. The workpiece color will progress from yellowish, to tan,
brown, milky gray, and darker gray.

after electroplating (1.5v from one of the AA batteries)

3 - disconnect workpiece from battery and polish with Wright's
Silver Cream.

After final polish - it's not perfect, but hey, it's "used". The 90% Ag dime is a size reference

NOTES:

If you are working on a metal work surface, be sure the battery leads
do not short out on the work surface, and drain the battery.

If the color progression in step 2 above is very slow or does not occur
it may be that the battery is dead or wired backwards, or the AgNO3
solution is depleted.

CAVEAT EMPTOR:

I have no idea what the thickness is of the resulting silver plating.
All I can say is that the pieces I have plated in two passes with
freshly-made 0.6M AgNO3 survived being polished with a soft
buffing wheel & jeweler's rouge.

WHERE TO GET ... ?

1 - SILVERPLATER polish/plater: from Caswell Plating
(http://www.caswellplating.com), $60 for 4 oz., plus shipping

2 - Silver Nitrate: available on-line - be sure to get pure AgNO3 crystals,
not applicator sticks, a weak "solution", "homeopathic pellets" or other
concoction that may be contaminated with other chemicals and/or may not
contain much/any AgNO3! With the Ag spot price around $20/troy ounce,
pure AgNO3 will probably cost at least $40 per (avoirdupois) ounce.

3 - "SoftScrub": unless you've already got a source, just make your own
from liquid detergent and sodium bicarbonate - about 50/50 mixture to
form a paste.

4 - Wright's Silver Cream: WalMart, online, etc.

=========================================================================

20140306 - An update for chemistry geeks ...

Regarding "Silverplater" - it's not magic, but it does seem to contain
a fair amount of Ag, probably as Ag(NH3)2, and possibly
micro-crystalline silica as the polishing agent. It does not have any odor,
e.g. no ammonia odor like some silver polishes. The plating "mechanism" seems
to be brisk rubbing.

An interesting twist on the possible ingredients in Caswell's "Silverplater":
while it has no discernible NH3 odor in the bottle, if the AgNO3 solution
on the wand gets contaminated with "Silverplater" residue from the workpiece,
it produces a definite NH3 odor.

Some experiments:

A - determine if rubbing Silverplater on base metal releases NH3

1 - place 2 drops of Silverplater on cotton ball

2 - rub vigorously on brass rod until some silver plate observed

3 - smell to determine is NH3 perceptible (negative)

4 - repeat near open container of 37% HCl (negative - no NH4Cl "smoke")

B - investigate the alleged Silverplater + AgNO3 (aq) reaction:

1 - in a small test tube, I mixed a couple drops of "Silverplater"
with a couple drops of 0.6M AgNO3 solution; results:

a - opaque white ppt, presumed to be AgCl

b - definite odor of NH3; NH4Cl "smoke" formed in presence HCl fumes

2 - added 30% NH4OH, one drop at a time:

1st drop -> ppt partially dissolved,

2nd drop -> more ppt dissolved

3rd drop -> all ppt dissolved,

C - conclusions:

1 - Since there is no evidence of free NH3 in the Silverplater product,
I suspect any NH3 used in its preparation has reacted completely or
dissipated from the product.

2 - Since there is no evidence of free NH3 from rubbing Silverplater
on brass to the point of depositing some Ag, I suspect that any free
NH3 resulting from the dissociation of the Ag(NH3)2:

a - is absorbed by H2O present in the cotton ball, and/or

b - reacts with the Cl- ions remaining from the initial reaction
of AgCl + NH4OH to form the diamine complex

hence no NH3 is released to present an odor or form the NH4Cl "smoke".

3 - the Silverplater product most likely contains Ag(NH3)2 diamine
complex, and Cl- ions in some form, probably as NH4Cl, and may contain
some NO3- ions, if AgNO3 was an ingredient used to form the AgCl
which ultimately reacted with excess NH4OH to form Ag(NH3)2.

[Doug Coulter]

Great post! Go Dave!

Dave was my lab assistant for awhile on (mostly) computer stuff - but also optics and "you name it". A good friend, you guys are going to be amazed down the road when he posts on his other batch of expertises. For this, his wife is running a small jewellery business, and this technique for recovering silverplate was just the thing for right now. You need it invented - Dave might be the guy. He doesn't have a running vacuum system just yet for PVD - he's got the parts, but it's a time issue.

FWIW, I'd bet that there is ammonium chloride in the mix. It's a great flux - eats everything, so the surface contamination doesn't have anything to stick to and is washed off.