Painted metal material -- question on fresnel...

[davision]

Okay, painted metal has always driven me crazy.

I know raw metal, like chrome, gold, silver, copper, aluminum etc. is supposed to have non-fresnel reflection (or at least a very high IOR if fresnel is used).

But what about painted metal like in the images I've attached? The blue and green dumpsters are the objects of interest.

When metal is painted like this, does it have fresnel reflection or not? It looks like it does to me, ... but then I start to wonder: what is it that makes it obviously metal when you see it in real life as opposed to looking like plastic or something else which also has a fresnel quality. The reflection's intensity maybe? Or a different fresnel ior?

One reason I find this is extra confusing is car paint. (Before VrayCarPaint material was around) I always read that you should use a non-fresnel base layer with very blurry reflections and then do clear coat on top with sharp, fresnel reflections. If the base paint is supposed to be non-fresnel then maybe the dumpster paint should be that way as well, because presumably there is no clear coat on a dumpster?

Thanks for any insight you can provide.

[Dariusz Makowski (Dadal)]

Heya

The best way to find out is to buy paint, learn how it works and do a test in garden.

From my experience I can tell u now that everything has IOR, fresnel reflection. Also the material for dumpster u would have to make a paint material and then I believe add a sophisticated bump layer to make it realistic. The bump will need to be a mixture of metal texture and paint itself. It would reflect and deal with light very differently based on the type of paint used as well as the gun and preasure, layers and so on during the painting process...

In moments like that I would just match it to reverences.

In case of car paints u need 3 layers, 1 metallic base, 2 flakes, 3 clear coat reflection.

Thanks, bye.

[Deflaminis]

As Dadal has said, everything has IOR in reality.

I would make the material as close to reality as possible. So maybe a vray blend mtl, using metal as the base layer (unpainted) and then putting a paint coat on top of it. I would use the scratches bump as a mask to show the metal material through it in certain places. For the most part however it's the paint material that you need to make, the scratches showing the metal underneath has a multitude of ways to accomplish it.

I hadn't heard that metals use non-fresnel reflections. I've had lots of luck using ward, high fresnel (like 10-20) for metals.

Your mileage may vary...

[davision]

Thanks for the input. I guess I shouldn't have said "no fresnel" on metals, but minimal is probably a better word. Once you get up to an IOR of 10 or above the effect is pretty subtle.

I'm mainly trying to figure out why paint on metal often looks so different than paint on a wood surface for instance. It seems much more reflective -- even if you were comparing it to a high glossy paint (applied to wood).

I'm guessing the IOR is considerably higher -- although not near 10, but maybe 2 or 3?

[Deflaminis]

I'm mainly trying to figure out why paint on metal often looks so different than paint on a wood surface for instance. It seems much more reflective -- even if you were comparing it to a high glossy paint (applied to wood).

I wonder if it's because it's sort of refractive so we can see the highlights through it. It's a good question...

[Dariusz Makowski (Dadal)]

Its because the paint is being absorbed differently by wood and metal. There fore it dry differently giving u different effects...

[Pixelcon]

I think the second photo you uploaded answers your question. The face that's perpendicular to the camera is a non-reflective deep blue whereas the top and side are reflecting! The first photo isn't giving much away but might help you find out a good IOR or falloff

[simmsimaging]

Thanks for the input. I guess I shouldn't have said "no fresnel" on metals, but minimal is probably a better word. Once you get up to an IOR of 10 or above the effect is pretty subtle.

I'm mainly trying to figure out why paint on metal often looks so different than paint on a wood surface for instance. It seems much more reflective -- even if you were comparing it to a high glossy paint (applied to wood).

I'm guessing the IOR is considerably higher -- although not near 10, but maybe 2 or 3?

I think you might be surprised how much your own understanding of what things are made of affect that conclusion that something "looks" more like painted metal, or plastic. i.e you know that dumpster is metal so it feels different than something with a similar surface would, that was obviously plastic.

That said, some of the difference comes from the way paint absorbs into surfaces, and how smooth they are, but if you totally paint over metal with a fully opaque paint I don't think the reflective qualities of the metal impact the final look in any real way. Only an anodized metal would allow the metal IOR to have much effect with colour, IMO.

Painted metals tend to have a smoother surface with less micro texture than plastics or woods so the glossiness is generally higher - that is the big difference in my opinion. A slight surface texture changes (say a procedural noise in the bump) can easily make a painted metal look like a painted plastic.

Carpaint is different in that, most often, you are using that high fresnel/non-fresnel base to simulate a metallic paint - which is not really representative of what the actual car metal would look like. There the increased reflectivity of the material is simulating the way the flakes pick up reflections from much different angles than the base metal/paint does.

That's my .02 anyway.