PLATING THICKNESS MEASUREMENT
In the plating industry, there are several different types of equipment used to measure thickness. In each, accurately plated standards are needed for calibration. Different standards are needed for different thickness ranges and different substrates (the metal or metals underneath the gold).I haven't kept up with this, but I think that
x-ray equipment is most commonly used today.
In the dark ages, when I was in plating, we mainly used
beta backscattering equipment, such as the Betascope or the Microderm. They were quite accurate but they required the use of several radioactive isotopes. I'm sure they wouldn't pass OSHA's muster today.
We also had another type, which is still used, made by
Kocour. It uses a specific solution and current to actually dissolve about an 1/8" dia. spot of gold plating (or, whatever type plating you're measuring). The thicker the gold, the longer it takes to dissolve through it. When the solution penetrates through the gold and into the metal layer below, the current changes abruptly, the machine automatically shuts off, and the time is registered. With the right standards, it can be quite accurate.
You might get lucky and pick up one of these old machines for a song. Here again, though, without proper standards, they are worthless.
Sectioning and Mounting. Another common way is to plate a thick backup layer of something hard, like nickel, onto the gold, cut the part into sections, mount and polish a section, and measure the thickness with an optical comparator scale built into the lens of a high power metallurgical microscope. I've done a lot of that.
For determining gold values, the problem with all the above methods, is that you're only measuring the gold in one area. Plating is never 100% uniform. It is always thicker on the edges and thinner in the recesses, although, with some types of baths, this effect is minimized. To determine the value of a part, you need the average thickness. All the above methods suffer from that problem, although each can be used to test at multiple places on the part and come up with some sort of a half-a**ed average thickness.
Strip and Weigh. With a scale that will measure down to about .00001 grams, you might be able to get an half-a**ed estimate of the average thickness by measuring and calculating the plated surface area, completely dissolving everything away from the gold, and then collecting the gold and weighing it. It's easy to see, though, how this method is potentially fraught with very severe difficulties. I don't think I need to list them. Due to the small quantities of gold involved when only doing one part, this is best done on a large sample. With a large sample, you could also get away with a lesser scale.
Gold Recovery. With a large sample and, if the parts are all the same, you could calculate the surface area and then recover, refine, and weigh the gold. The average thickness could then be quite accurately calculated. This might be the best way of all.
when I look at this under a 30x hand held microscope I can clearly see the thickness of the plated layer, if it was 12 micro inches, 12 millionths of an inch right? do you think I could see the layer as a clear and seperate layer?
Are you talking about first peeling the gold off and then looking at the edge or, are you dissolving everything but the gold foil and then looking at the edge? Whether you can see it or not, this would be a very poor way of judging the thickness. Very, very subjective. I could easily see a 100-200% error in doing this. Sectioning and mounting, as discussed above, would be the only way to do this with any accuracy at all.