I came across a very interesting article on airbrush titled "SEM/EDS Analysis of an Iwata CM-B and an HP-B" by Zsolt.
Zsolt Miklós KOVÁCS VAJNA is a Full Professor of Electronics at Department of Electronics for Automation, Faculty of Engineering, University of Brescia. He was doing a "color study" for artists in 2008. Just like all good scientist who cannot resist a temptation, he ended up doing a "scanning electron microscopy" and "Energy Dispersive X-ray Spectroscopy" study on the tools he used, a pair of Iwata airbrush. The airbrushs are a CM-B (Custom Micro) and a HP-B. The HP-B is similar to the Iwata Eclipse HP-CS that many of us use for modeling, but with a smaller cup.
The article is lengthy and very technical. Here I summarize his observations.
(1) The airbrush body was made of brass, then, copper, nickel and chrome triple plated to assure smooth, no-binding operation.
(2) The nozzle tip was made of nickel based superalloy. This class of alloy was used mostly in aerospace jet engine turbine blade applications.
(3) The needle is just plain 304 stainless steel. He compared it to the Paasche needle and noted that Paasche used molybdenum dopped steel which is superior to the 304. He concluded that the much higher price of the Iwata needle is not because of material.
In an companion article, Zsolt tried to improve the needle by micro-polishing them. I noticed that the Iwata needle has an uniform and gentle taper. This is the 0.19 mm needle.
By comparison, the needles of the Badger 155 and 3155 posted at Don Winter web site had a steeper and multiple step taper. These are the 0.76 and 0.5 mm needles. The needle body are all 1.2 mm in diameter as the Iwata.