How do I know what type of gold, platinum or silver I have?

Pure gold is 24carat and many countries use pure gold, or 22ct for their jewellery, but generally speaking the Australian market prefers the look of gold mixed with alloys. 

This process is quite regulated and jewellery should have a stamp mark indicating the gold content.
 

For example: 

9ct gold is stamped either9ct, 9k, 375.
10ct gold is stamped either 10ct, 10k, 416.
14ct gold is stamped either14ct, 14k, 585.
18ct gold is stamped either18ct, 18k, 750

21/22/23/24 Carat gold quite often will not have a stamp mark
Platinum – stamped 950, 950PT, Plat
Silver – 925, StgSil, SSil, Stg. (Most silver jewellery is Sterling Silver)
Other silver – 800.
Jewellery marked with GF, GP, or RG are gold plated
Jewellery marked with 9ct/StgSil, 9k/925 or variations mean that you have a 9ct gold sleeve with silver inside; this can apply to chains, bracelets and bangles.

I suggest you visit www.goldtester.net and www.HowToTestGold.com for more information on testing Gold.

and this RSS feed, which I will add to my website gives the latest precious metal scrap prices.

  http://www.cooksongold.com/mp/rss_scrap.jsp