Immersion plating using PNP solutions and adjustable power supply

[beaner82]

I was tired of racking my brain over this and swallowed my pride to post a question!

I have a variable power supply from 3-12V and 2amps that I use for pen plating. It's only variable control is the voltage. I do jewelry work and at times I need to plate whole pieces rather than just detailed work. So I got a wand for brush plating so that I would not have to spend so much time pen plating large areas, and to also try immersion plating. I decided to try an immerion plating with the PNP silver solution. I am unsure as to the exact voltage needed. I notice with the PNP sets that the power supply is set at 1.7 volts but have read other posts with people doing brush plating with a variable power supply in which a higher voltage was suggested like 4-10 volts for silver. Why is it different? Does the same surface area equation apply for amperage even though I am using a more concentrated solution? How will I know what is the right voltage needed?

I am also experimenting with my power supply as it's lowest voltage setting is only 3 volts. So I plugged in the power supply to a rheostat in hopes that as I reduced the voltage supplied to the power supply by the rheostat, that it would in turn reduce the output voltage of the power supply. I have yet to get a voltmeter to confirm this though. So I don't know if this attempt is futile or not.

So, I experimented with the immersion plating with the silver PNP solution setting my rigged power supply-rheostat to what I thought was about 1.7 volts. My brass piece intended to be plated was small so I barely had the wand in the solution, and when I dipped it, it immediately turned black. I know this may be an indication of the voltage being too high or too low, but which is it?

I would then buff the piece of the dark smut and reveal some silver sheen, and then dip again with the same results. I did this maybe 5 times or so, but while the end result was a silver color, it wasn't that bright shiny silver, even after buffing. If the piece turns black in the solution, will it still plate if left there longer, or does the black stuff prevent the accumulation of the plating?

Any thoughts to the innerworkings of my mind here

Thanks in advance!

[engineerscott]

I've never tried to used the PNP solution for immersion plating but from your descriptions it sounds like you are applying too much voltage (and subsequently too much current). You do really need a voltmeter wired to your anode and cathode to learn anything from your experimentation.

What size rheostat are you using? I would use a linear taper (not a log taper which are frequently used for volume controls) rheostat, say a 1kohm or at least a 100 ohm. Start with the rheostat turned to its maximum resistance setting then immerse your item in the plating solution. Hopefully if you have enough resistance you will see very slow or no plating occurring (if you see aggressive plating you need a bigger (higher resistance rheostat). *Slowly* dial the resistance on your rheostat down and start to look for signs of plating (bubbling, subtle change of color of item,etc.). Once you see mild plating leave the rheostat alone and leave the item in solution until you believe you have achieved the desired plating thickness (you're just going to have to judge this by eye and the seat of your pants.). This may get you what you want, however since I have never tried to use the PNP solution in this fashion no warranty is expressed or implied . Good luck.