  Anodized foils. 
These NASA-surplus tantalum foils have been anodized to various attractive shades of green, pink and purple.  Not sure if NASA wanted them colored this way, or if it was just accidental.   I have a story about how anodizing works: It's about titanium, but the principle is the same for any metal that forms a clear oxide layer. 
Source: Ethan Currens 
Contributor: Ethan Currens 
Acquired: 1 July, 2006 
Text Updated: 19 November, 2007 
Price: Donated 
Size: 2" 
Purity: 99.99%
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