|Postage stamp cover.
People who collect stamps like to have "first day covers" which contain a sample of the stamp canceled in a fancy way. This one also contains a sort of reproduction of the stamp in, amazingly, tantalum foil with colors created by careful oxidation. It's iridescently beautiful, though the tantalum foil version of the stamp is not a legal-tender sort of stamp. Here is a picture of the whole package showing the real stamps next to the decorative tantalum version:
Warut Roonguthai, who kindly provided this sample, sent the following information about it and the similar tantalum version he sent:
I believe that Royal Selangor (the company that produces FDCs (First Day Covers) for Malaysia) put metal cachets on FDCs because they are an expert in making metal objects/arts. So they want to show their ability to make those cachets.There are other versions of cachets like pewter and silver, but I don't think you are interested in such naive metals, and they can't be anodized to create colors. Royal Selangor started their business with pewter because there are a lot of tin deposits (in the form of cassiterite) in Malaysia and the southern part of Thailand.
The tantalum cachet I gave you is the only one they have produced! Now they only use niobium for making colorful cachets for FDCs since tantalum is much more expensive than niobium.
Source: Warut Roonguthai
Contributor: Warut Roonguthai
Acquired: 16 August, 2004
Text Updated: 29 January, 2009