Re: feather color

[Larry Woolf <larry.woolf@GAT.COM>]

> At 10:11 PM 1/9/01 -0600, cliff parker wrote:
>
> > interference such as that observed in thin films such as
> > soap bubbles?
> Yes.  Interference effects are responsible for
>  -- those funny anti-counterfeiting features on money and product labels


Interference pigments are also used on US currency.  For example, the new
$20 bills use interference pigments for the 20 on the lower right hand
corner of the bill.  The 20 appears green when viewed straight on, but
looks black at high angles.  The flakes are easily visible at 30X
magnification.  They consist of a thin semi-opaque metal layer, typically
Cr (about 5 nm) followed by a layer of SiO2 - the thickness is tuned to
give the desired color- followed by a thick reflecting metal (usually Al)
layer and then the same SiO2 and Cr layers as stated above so that the
flake is symmetric.  Interference pigments are also used in many consumer
electronics devices, golf clubs, bikes, etc.  These pigments are made by
Flex Products of Santa Rosa, CA.

Dr. Lawrence D. Woolf; Phone: (858)-455-4475; www.sci-ed-ga.org
General Atomics; 3550 General Atomics Court; San Diego CA 92121-1194