Just a smidge more technical stuff for those who are interested....

The rest of you feel free to sleep through this part....

QUOTE(Splicer @ Feb 15 2008, 05:41 PM) [snapback]515462[/snapback]
I did not mean to suggest that material properties play no role, but if it were all about material properties and not about shape and thickness, Richard Binder and John Mottishaw would not be able to take a firm semiflex like a Namiki Falcon and turn it into a near-true flex.
My suspicion is that the more you shape and thin the nib to flex, the more closer you come to the point where gold will bend rather than flex. I'm certain that you're right that the best possible flex nibs can be made from steel rather than gold. I also suspect that corrosion is much less of an issue with modern steels. I've never owned a steel-nib fountain pen long enough to see corrosion, but then again, I've never owned a steel-nibbed fountain pen for more than 20 years. And yes, I do have dip pens that are toast after sitting around for only a decade, so I have no doubt that this was once a much larger issue than it is (or should be) today.
My bad for over generalizing... In the case where the quality of the shaping is "equal" to the intent of flex, the material is what
makes the difference in what is "best". Yes a well shaped gold flex nib will be better than a poorly shaped steel one, but this discussion is about materials not the skill of the nibmeister.
Most materials have an "elastic" region for deflection under load and when the elastic load is exceeded a plastic region for deformation under load. The rate of elasticity is different for different material, that is the load for a given deflection on a given cross sectional area. In engineering terms this is the Modulus of Elasticity (given in a unitized form) and the yield limit. These are given per unit cross sectional area subjected to the load, so yes the absolute value deceases with thickness, but the unitized one is independent of load and is an intrinsic material property.
As you go to softer (more malleable) materials have a lower load (per unit area) where the yield point is reached, like gold with higher purity, the line between springy flex nib and bent dud get thinner and thinner. Gold is known for being UNspringy in nature, or exceptionally malleable. This makes it the antithesis of what you'd want based on pure material properties.
In his article Flex:A Disaster in the Making Richard Binder has a graph (http://www.richardspens.com/?page=ref_info/nib_disaster.htm) that shows the green/yellow area and the red area... The ratio of those relative to each other is determined by the material properties. In other words some materials have a very small green area and a very large red one. Others have exactly the opposite. Pure gold is one with a very small green area and spring steel is one with a large green area. Most grades of Titanium alloy fall in between, as do progressive grade of gold alloy. Or course with alloys there is also the issue of what effect the alloying material has on this ratio. Two different 14k alloys can be very different in nature. If you alloyed gold with lead you'd get something quite soft compared to alloying it with the same amount of nickel. FWIW nickel is a common alloying material for white gold, and lead is generally not used with gold.
In summary, shaping matters but the best shaping in the world won't make the material do something beyond it capability. Again Richard Binder mentions preferring to use 14K nibs for flex rather than 18k for this reason.
Everyone asleep now?