One can use a variety of substances to “mask off” areas in plating.
I’ve even used magic marker “Sharpies” to coat or mask off.
Afterwards, I fill up a small jar with acetone, put the item that
was plated in the solution in the jar, and then suspend the jar in a
working ultrasonic. The ink used for masking will literally fly off
in seconds. A thorough rinse, steam, and dry afterwards is all it
takes to remove it.
Nail polish works great too, but it takes more time to dry, and also
to dissolve away later.
I have an idea for you. Think about reversing the leads on the
If it were me in your situation, I would first prep the insides of
the cup as perfect and clean as I could, getting it ready for
plating. Heat up the 24kt plating solution to the proper temp, setup
the cup so it is as level and stable as can be. Fill the cup up to
it’s brim with the 24kt plating solution, attach the Negative lead
from the rectifier to somewhere on the silver cup that is connected
(to conduct electricity) to the bowl, like say the handle, and attach
the Positve lead from the rectifier with it’s wire, clipped to a
strip of 24kt rolled out thin and long to suspend in the solution in
Then with rectifier turned on(you’ll have to probably adjust the
voltage up a bit from the usual), suspend your gold strip into the
the 24kt gold solution, and move it around and around circularly
inside the cup near it’s sidewalls, with the very end of the gold
strip also near the floor of the cup too. You can do this as long as
you want at power voltages to build up the micron thicknesses. While
you do this, bear in mind there is to be NO CONTACT between the gold
strip to the silver body. If your 24kt strip is long enough, you can
bend the end into a smaller perpendicular circle shape which would
plate more uniformly to inside walls at the moment as it moves
around and up and down. That’s not necessary, but just a thought to
help plating thicknesses
When done turn off the rectifier. Pour the plating solution back
into it’s bottle for reuse.
IF after rinsing, the plating color is a bit brownish in areas, wet
the insides of the cup, put a couple of spoonfuls of baking soda
into the cup making a slurry, and with your fingers (or natural hair
brush) rub the innards all over with the slurry. This should bring
the uniform gold color back.
If you want before you start all this, you can use a Sharpie to coat
the top edge of the cup and slightly down the outside, insuring no
gold plating gets there by accident.
Remember to place the cup onto a non-conductive stable/level surface
for the plating proceedure, wood will do just fine.
I would think that people in the business of doing plating would
understand this approach and be willing to plate it this way for
you, IF you do all the prep work and clean up afterwards. They can
just reverse hookup the anodes, put in the 24kt solution, and plate
the innards this way without submersing the whole item. Shouldn’t
take them more than say 15 minutes to just do this.
Is there a jewelry repair person mear where you live? If so, they
might likely have a plating setup and be willing to undertake this
approach (for a fee)