"Chris R" <car### [at] comcastnet> wrote:

> First, I pulled some images of rusted iron and created color palettes from them
> that I am now using to create color_maps for rust, rather than the ones I
> invented earlier.  I think these are better looking than the original.  I also
> took your suggestion and increased the rust density at the bottoms of vertical
> posts, and created less shiny version of iron with darkening from grime that
> carries over to the rust as well.
>
> The vertical bars had striations that I found in pulled iron images.  I fixed
> how they are formed so they don't get reflected in the rusty areas, and I
> updated the rust pattern to be more realistic as well.  The horizontal bars
> really only changed by using the new rust color palette, and by applying the
> grime to apply mostly to the top of the bar where it would rest.
>
> Finally, I adjusted the length of the cord to hang the lightbulb down further so
> it shows up in a 16:9 rendering.
>
> The next improvements will come in the walls, then probably the floor, and then
> I'll get back to Cogito himself.
>
> -- Chris R

Hi Chris,

It's great that you're pursuing changes based on observations and suggestions.
I will also acknowledge upfront that it's going to be a challenging task, since
I myself have found creating a realistic, or even satisfying rust texture to be
a very challenging task.

Trying not to be too negative / overly critical (it's not my render) but:

Whatever you have right now --- just isn't doing it for me.  It may be the
lighting, it may be the textures, or the normals, or the geometry, ...   it's
always very hard to tell.   But it all seems very --- flat, or washed out, or
muddied together.

Maybe experiment with a more grazing lighting angle - perhaps from a fill light
(which could plausibly be a hallway light) or an HDR light source.
I have always found that creating textures from photographs to be incredibly
difficult, not just from the perspective of creating a suitable pattern, but
also simply getting the basic pigment colors right.

Having said all that, I'm in the middle of daisy-chaining together a completely
ridiculous number of algorithms to make some decent wood textures, and it's like
doing a mini-PhD in computer graphics.  (Huge shout-out to jr who's been working
behind-the-scenes for nearly/over a month to get even a small part of the
procedural workflow implemented!)
I've done some searching for an extant procedural rust texture, to see if any
analogous work has been done, and most of what I've found is (to my
eye/taste/expectation) crap.

My suggestions at this stage would be to simply try and find examples of things
that _look good_.   They might be photos, they might be restoration videos from
youtube, or they might be CG textures that are in movies or software packages.

https://www.texturecan.com/details/73/

I have hundreds of pounds of antique/vintage tools that I've de-rusted and
restored to working order - so much, that my kitchen had a layer of reddish dust
that I had to wipe down.

"Realistic" rust is likely going to be a huge challenge to pull off, simply
because that sort of organic, developmental change exhibits such a wide degree
of variation - due to age, base allow, wet-dry cycles, whether static or in-use,
etc.

For your scene(s), I'd focus on something practical, but still aesthetically
acceptable.  To achieve that, I think you're looking at meshes or isosurfaces to
get the required surface displacement that I'd don't think a simple normal can
provide, and probably a layered texture at a minimum.

Rust is fundamentally an electrochemical phenomemon, expanding outward from
defects in the crystal structure that channel the oxidation process.  It
therefore tends to be very patchy, expanding from localized defect centers.

There are two main forms of iron oxides - magnetite (Fe3O4) which is black, and
hematite (Fe2O3) which is reddish brown. (you also have the hydroxides and
oxyhydroxides mixed in there....)
Aside from that, it's important to realize that when iron rusts, it becomes a
new chemical compound, which has a different density, and so it expands.  That
gives you powdery "blooms", cracking, flaking, and when material is lost, deep
pitting.
https://en.wikipedia.org/wiki/Rust
Which is why at the moment, I'm thinking that most of what you're doing will
benefit the most from geometry, normals, and lighting (which accentuates the
first two).

Also, there's the issue of particle size, which amazingly, gives you different
colors for what are chemically the same oxide.
https://www.911metallurgist.com/iron-oxide-pigments/
So you can have an interesting gradient of colors going from black through red,
orange, and up to yellow, sometimes with some purple mixed in.

Lots to think about, research, and learn, but better that you're also making
progress and not doing _too_ much analysis, which leads to paralysis.
Hope that "helps".  ;)

- BW

(also attached, find a procedural rust that I found on Wayback - the rightmost
is something like what I think you're generally shooting for)

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