Elemental Tales: Comic 7

Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.  Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal.  Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light.  There are many metals that can be anodized to produce a wide array of colors, such as aluminum, titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum.

In the case of niobium, anodizing niobium generates an array of different colors without dyes, for which it is used in various things such as jewelry and commemorative coins.  The color formed is dependent on the thickness of the oxide (which is determined by the anodizing voltage); it is caused by the interference of light reflecting off the oxide surface with light traveling through it and reflecting off the underlying metal surface.

Here are a few examples of anodized niobium jewelry and coins:

1) cdn3.bigcommerce.com/s-pri7p/p…

2) www.karenhunterjewellery.com/Q…

3) www.coinweek.com/wp-content/up…

 

Coal (from the Old English term col, which has meant "mineral of fossilized carbon" since the 13th century), is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams.  Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.