Testing Gold plating on bronze

[snoman701]

I have been getting a reasonable amount of gold plating. This whole gold thing has taught me that I'm pretty color blind. I have trouble differentiating between a brassy color and gold.

So, I test with stannous.

Well, I ran in to trouble...maybe.

Gold plated bronze, or so I think? So I put a drop of HCl and a drop of HNO3 on the item. Let it sit...then pick it up and put it in a drop of stannous. In this case though, it just turns black... Is the HCl reacting with the tin in the bronze to essentially form gold chloride & tin chloride, which then forms the black liquid.

I didn't try, but I think the best way to tell is to dilute out the black and see if it's purple???

 

[kernels]

I would think a 50% diluted drop of Nitric would be all you would need to distinguish ? It will react with copper or copper based alloys and turn blueish. Wont have any reaction on gold.

It is also useful to ask yourself what purpose gold would serve where you think it may be plated. It is either there for corrosion prevention, decoration or for electrical contact.

 

[snoman701]

I thought that gold plated items will often still react due to the porosity of the plating when it's thin.

In this case, the gold would be for corrosion. It's also with a batch of parts that very definitely are gold plated...or at least some of them are. Gold on copper, brass, aluminum, and possibly bronze.

I almost grabbed a gold plated faucet today, mostly because I was curious....but then decided I've got enough to do!

 

[kernels]

If the gold is so thin that it is porous, it sounds like you may be wasting your time ? I'm sure even ENIG which I don't personally bother to recover will stand up to a drop of diluted Nitric.

 

[g_axelsson]

A drop of nitric acid is a quick way to test for plating. If the acid is reacting with the base metal through a gold plated surface then the plating will fall off and can be seen like a fine powder if thin and as a solid foil if it is thick.

Look at the picture of the pieces I dissolved in a test tube, it was lightly plated brass supports and the foil broke down into fine dust. The following fingers were holding together good, proving the plating was thick.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=23737#p250557

Göran