Sciencemadness Discussion Board

Platinum Jewelry

bereal511 - 14-12-2005 at 18:34

I was wondering what the composition of platinum jewelry was and their substrates (if plated). I wanted to do some catalytic reactions with ammonia to see if I could produce nitric acid as a science project, but I wasn't sure whether the composition would affect the reactions. Also, I was a bit skeptical of this seller of platinum jewelry. I have no knowledge of platinum-plated jewelry prices, so I wasn't sure if these prices were too cheap to be platinum. How would I check to see if it was platinum if I did buy it?

http://stores.ebay.com/MG-Jewelry_Platinum-Chain-Necklaces_W...

BromicAcid - 14-12-2005 at 18:43

Quote:
This rhodium (platinum) chain necklace is simply amazing, because it will always stay shiny and will never lose its great platinum expensive look. Rhodium is a raw form of platinum and it's one of the most expensive and precious metals on Earth. This chain necklace has several layers of heavy rhodium plating over a heart of semiprecious metals, resulting in a much heavier thickness of rhodium (platinum). This increases durability and wearability.
Hummm... it looks like they consider rhodium the same as platinum, I wonder if there is even any platinum in the necklace? I know platinum is found native mixed with other elements in its region of the periodic table and I'm not sure what the native metal is called, but from that description the necklace is rhodium plated, it sounds somewhat thick but you should ask the seller.

[Edited on 12/15/2005 by BromicAcid]

s1 - 15-12-2005 at 05:59

Looking at the price of them I would say that they are rhodium plate sterling silver.

zoomer - 15-12-2005 at 08:02

Pure platinum is never used in commercial jewelry today, it is always alloyed 5%-15% with a variety of metals, especially iridium and palladium. It is rarely if ever plated. However, most white gold (Au/Ni) jewelry is today electrolessly dip-plated with rhodium to increase its "whiteness." Any commercial jeweler can dip-plate a ring for you in about 5 minutes. It is likely that the product described in your post is a less expensive metal chain plated in this manner. Incidentally, this type of plating is only a few mils thick and typically lasts only a few years at best.

Unless you score big at a garage sale, platinum jewelry always costs more per gram than the raw materials. However, you can sometimes buy much smaller amounts with jewelry, which can be easier on a limited budget.

A good discussion of platinum jewelry alloys and how they are marked is in this month's Ganoksin newsletter (an industry source).

http://www.ganoksin.com/borisat/nenam/platinum-alloys.htm

neutrino - 15-12-2005 at 10:19

My advice is to go to a jeweler and get an old platinum wedding band. I got a 1-pennyweight one (~1.5g) for about the spot price ($35 back then). It probably isn't totally pure, but a thin sheet (yes, I pounded a piece flat) glows in an atmosphere of acetone and air, so it should be pure enough for any catalytic use. Remember that many other platinum group metals (Ir, Pd, Rh, etc.) are excellent catalysts, comparable to Pt itself.

garage chemist - 15-12-2005 at 13:39

The ammonia---> NO2 reaction supposedly works with copper as catalyst too. Use a thin copper wire, preheat it strongly and put it into an erlenmeyer with some concentrated ammonia solution in it. If it works the wire will continue to glow and white smoke (ammonium nitrate) and brown gas (NO2) will become visible.

Maybe some of the nitrogen in the ammonia is lost as N2 this way, this might be the reason that industry doesn't use this process.