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aleksey voz wrote: only thing i've found is to jack up the IOR, but that doesn't seem like the right move

Why not? It's pretty right method. The material layers are stacked this way:
1) Reflection1 (layer weight is multiplied by the weight computed from IOR)
2) Reflection2 (layer weight is multiplied by the weight computed from IOR)
3) Transmission (only weight value)
4) Translucent (only weight value)
5) SSS (only weight value)
6) Diffuse (only weight value)

Each layer weight determines the portion of layer contribution stack based (high level layers with largest priority).
E.g. the first layer has weight=0.3, then all underlying layers have 1-0.3=0.7 multiplier.
For example, the second layer has 0.4 weight setting, while after the first layer reduction it means the second has 0.7*0.4=0.28 contribution in total.
While the layers below the second one have 0.7*(1-0.4)=0.42 weight, and so on.
So if you make weight=1 for top layer you will hide underlying layers.
This way you can make a glass, with reflection1 and transmission with same IOR values, you can make different IORs if you want. You may stack two reflections on top of transmission.
The Color value is used to multiply reflectivity after layer contribution is determined by weight x IOR_weight. The Color doesn't make space for other layers, everything is controlled by weights and IORs for reflections.

To make Chrome you can make Reflection1 weight=1, IOR=20 or 50 (for example) and Color with some slight blue tint, roughness=0. The second reflection may have larger roughness=0.3 white color.

Other rendereres have same material rules, but sometimes there is metallic/conductor IOR with additional to IOR setting. This can be replaced with just high value of the current single setting IOR.

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aleksey voz wrote: By the way is there a material demo collection or something? To use as reference?

I am going to write an online documentation on materials after 0.65 release is out with shaderball examples, how to make metals, flakes, glass, wood facture with procedural noise. For example 0.63 with nice fixes is almost ready.

This is due to existance of 2 Fresnel IOR modes: dielectric and conductor. Ours is dielectric at the moment. Conductor is for metals and it has complex value (2 settings ior and k, and 1 switch between modes). Fresnel dielectric can mimic conductors with high IOR values and look similar but with less controls (and less real physics). Renderers usually have either one or both modes. Not a problem to add conductor, I just wanted to make material GUI simpler, however it already has many other settings, especially that long material box in node editor canvas

A lot of metalls can be nicelly implemented with 2 or even more reflection layers stacked on top of each other. Generally there is a medium glossy reflection 2 and clear mirror layer on top of that.
Reflection 1 can be a specular mirror coating with roughness = 0 and IOR = 1.5 while Reflection 2 may have higher fuzzy roughness = 0.3 with IOR = 2 and it will sit below the first reflection. Then a diffuse layer is placed with some color.

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ssjenforcer wrote: I have the colour texture and glossyness and reflection which I know where to map in the material, but what about metallic?

CentiLeo has roughness, not glossyness. They are reverse to each other. You either reverse the glossyness texture using output black = 1 and output white = 0 or enable "Use glossyness" flag in material settings.
As for metallic - it's not directly supported right now, it can be used to tune behavior of reflection parameters. I will make a slot and a mode for it. Currently the picture of metallic can be assigned to IOR, but the range of bitmap metallic should be adjusted, because for metals the IOR should be larger than one. E.g. you can experiment with metallic bitmap output black = 1.5 and output white = 4.0.
Reflection1 and Reflection2 are absolutelly the same reflection, but there are 2 of them one on top of another one to get more freedom in hand for various metal implementations.

Actually to change the output range of Bitmap image the Map black/white can be changed. They help to scale or invert the image. This is an example of invert:


You can also change the distribution of the values between black and white colors of the image. For example this can be done using CentiLeo gradient node. Just look that middle grey values in the gradient ramp are changed to prefer darker values for the larger part of the input range.

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Wuzhongjian wrote: why use two reflection when making metals,and does Reflection 2 use the same IOR as Reflection 1does?

It's defenitelly up to user to use one or two reflections. You can setup differernt IORs and roughness for them of course. This is done for artistic freedom