Posted by TVP on January 08, 2010 at 09:19:21:
In Reply to: Color Etch of Pure Aluminum posted by Dongok Kim on December 30, 2009 at 04:05:30:
Pure Al can be "color etched" with Barker's reagent, meaning that different colors can be seen when viewing the etched microstructure with polarized light. Viewing with polarized light + a sensitive tint filter is even better. Weck's reagent is another that can be used for color etching, which consists of 1 g NaOH + 4 g KMNO4 + 100 mL H2O (etch up to 30-60 s). View with polarized light + sensitive tint filter for best results. Alternatively, this can be split into two steps: 1st etch with 2 g NaOH + 100 mL H2O (30-60 s), then etch with 4 g KMNO4 + 100 mL H2O + 1 g NaOH (~ 15 s). Struers has a good technical article on this method on their website:
www.struers.com/resources/elements/12/2431/38art1.pdf