Due to the fact that silver is very porous, it entraps a
lot of polish in it and therefore, you should always bear in mind
that a good cleaning preparation is essential.
Silver is not necessarily any more porous than other jewelry metals.
If you’ve got porosity, it generally means you’ve got problems in
how you produce your metals. Porosity will usually only be a problem
with castings, not sheet and wire. But porosity can indeed be a
problem with some silver castings… One thing that will help, if
you’re able to do it, is tumbling the items with steel shot. the
burnishing action will nicely close up most surface porosity.
The first step to do is to give the silver item to be plated is
a good surface and also a good polish.
Very true. Though there are some plating procedures, using
brightened baths, that can increase the polish and finish quality on
an item being plated, these are not the usual processes used for
small scale plating. So yes, get a perfect polish on it first, if
you wish a good polish on your silver.
Then, clean the silver in an ultrasonic cleaner for at least 15
minutes and then rinse preferrably with distilled purified water.
DO NO TOUCH the silver items with your bare hands,
True enough, at least the bit about not touching the work after
cleaning. Note, however, that cleaning silver for long time periods in
an ultrasonic can be a problem. If the silver is rolled or drawn
wire, dense and solid, etc, then usually it will withstand this
treatment. But the very types of silver the post worries about, that
with much porosity, coupled with any of the ultrasonics that are
reasonably powerful, can result in etching away of the fine polish
on the silver, since the surface defects concentrate the ultrasonic
action at those points, leaving whitish streaks.
Though the ultrasonic is a common method of cleaning things before
plating, it’s not actually the most effective. Among other things,
many cleaning solutions used commonly in ultrasonics to remove
buffing compounds, etc, contain materials such as lanolin, or various
other components, that can leave a surface residue on the metal. I
recommend only brief ultrasonic cleaning, to remove the bulk of the
polish compound that’s visible to the eye, rather than extended
cleaning to try and remove invisible bits in pores. If you then
have a steam cleaner, use it as well, since it will often remove more
of what the ultrasonic missed.
By far the most effective cleaning method for getting the metal
really, chemically, clean prior to plating is electro cleaning.
Before doing this, of course you’d do the normal cleaning of visible
polish compounds. If you don’t have an ultrasonic, just simmering
the item in a hot solution of strong cleaner such as TSP, or even
lye, will remove most of the dirt, without the risk that an
ultrasonic has of damaging the finish.
Then, using a commercially available electro cleaning solution
(usually sold as a dry powder to which you add distilled water, and
most commonly it is mostly just lye or another strong alkali), you
clean the item electrolytically. the gas bubbles generated by the
current flow through the item, coupled with the electrical flow
itself which creates an ionic cleaning effect, will be highly
effective. And the power supply and setup you use for this is the
same as for plating. People who have trouble getting a plating
deposit to adhere well, which can be gold plating over silver, or
sometimes rhodium, or other types of plating, usually find the
problem goes away when they start using electro cleaning.
now, as noted in the prior post, rinse in distilled water. Keep the
piece immersed in the water until you’re ready to go to the next
step, as exposure to air can allow slight oxidation to start,
affecting the plating.
An important addition to the prior post is to note that if you wish
the gold plated deposit to last permanently, you have to do more than
just gold plate over the silver. The reason is that gold plating
applied directly over the silver will, over time, dissipate into the
silver, and the color will appear to fade. If you put a nice gold
plate on the silver today, and come back and look at it in two years,
you’ll find it’s a pale remnant of the original color. This is NOT
wear. it’s the gold dissipating into the silver, and the silver
into the gold, so that you end up with a surface that’s no longer
just the gold, but an alloy of both the gold and silver.
To prevent this, you have to apply a protective plated layer of
another metal which the gold cannot dissipate into. Copper can work,
though it’s not the best, since over time, the copper can oxidize
underneath the gold plating, since often the gold layer is a bit
porous. This results in discoloration of the plating over time. the
best is to first put a copper under plate on, just thick enough so
the whole item is fully copper colored, and then plate with . The
nickel is put on just till the copper color is masked, and the item
is again fully white color. It’s important to rinse in distilled
water between each step, and also not to allow the item to dry or
remain exposed to air, especially after the nickel plate.
Nickel can oxidize, forming a passivated surface that will plate
with gold, but not let it adhere. To prevent this, one dips the item
in a dilute acid bath to dissolve the surface oxides if any are
present, just before the gold plating it done, (with of course, a
careful rinse in distilled water after the acid dip.) This is not
usually needed if one is doing everything in a sequence, going from
the nickel to a rinse to the gold, without waiting. But if you’re
waiting any length of time between the nickel underplate and the gold
plating, the acid dip will considerably improve the results.
Both copper and nickel plating baths are available in brightened
versions, which will help improve the surface polish, or at least
keep the repeated plating steps from deteriorating the surface
polish. I recommend them, but whether you need it will depend on
the item, and how thick your plated deposits are.
Anyway, you’ll find the gold plate you apply over the copper and
then the nickel underplates, will be quite durable and long lasting.
The bath temperature should be between 120 and 160. Changes in
temperature will affect the colour of the plating. Try to keep the
temperatures always the same.
Temperature recommendations vary with the bath composition. Use
what the bath manufacturer recommends. Also, if you’re using a
cyanide based gold bath, and over time, find that the color is no
longer as rich as it used to be, add a little bit of sodium or
potassium cyanide to the bath. Cyanide oxidizes over time, and as
baths get older, the amount of free cyanide in the bath is depleted.
it’s required for a good rich color, so when the bath starts to
produce a deposit that’s just not a nice bright color any more, the
addition of a little bit of additional cyanide will often work
wonders.
Obviously, this is not true if you’re using the non-cyanide based
baths. For beginners, this would be a wise and prudent
recommendation, since cyanides, though they produce probably better
quality plated deposits, are also considerably more dangerous to use,
if one isn’t well versed in safe handling of such chemicals. And the
non-cyanide solutions DO produce a quite acceptable result. The main
difference is they’re not as good at producing thicker/heavier
deposits, and they aren’t quite as good at getting down into
recesses.
Peter Rowe