Tips & Tricks - Metal Corrosion & Weathering

 

      When you get the chance, take a good look at the metals you see around you in everyday life.  Chances are, there is probably some indication of weathering.  Some of these elements could include things like discoloration, oxidation, mineral deposits, galvanization, or a host of other things.  At any rate, what's true about the metals you see is that there is story behind everything.  So whenever you're shading or texturing something, that's something you really need to to think about.  Sometimes it can be temping to just roll with a cranked spec weight and call it good, but in reality, it's pretty rare to find pure, untarnished metals in everyday life, and not adjusting anything else usually leaves things looking pretty boring.  Often times what our eyes actually see is protective paint, oxidation, mineral/dirt deposits, or galvanized coating over metals.  So that's why I made this blog.  Let's start off by taking a look at corrosion/weathering in the real world.

 
 

    So what does this mean for us as 3D artists?  Well, that means that what we see in the real world is usually an interesting mixture between the shiny, specular metal and other more diffused components caused by corrosion.  And... that also makes things a bit more complicated.  Once you introduce these elements of corrosion, you have to deal with a more complex utilization of diffuse weight, spec weight, bump, etc.  Lets take a look at this picture for a minute to serve as an example to what we're talking about here...

 
 

A picture I took walking to work one day

    I like this picture because it shows a few different things.  First of all, if you compare the pipe on the outside to the piping in the middle to the protective ring against the wall, each element features very different kinds of weathering patterns.  This could be due to, perhaps, certain pieces being changed out at different times, but I think the main driving factor behind all this is that these are just fundamentally separate materials that react differently to the environment.  The heavily rusted pipe on the left is almost entirely rusted out with only a few traces of the shiny, specular metal breaking through the layer of rust.  The piping in the middle features an interesting pattern where weathering happens both on top of the protective black coat as mineral deposits and also as small patches of rust that break through the protective coating and expose the metal underneath.   For the ring, you'll notice a spotted rust pattern along with what seems to be a super thin, semi-transparent film of rust that tints the specular reflections into a golden hue.  There's a lot you could say about these pieces, but in general, it just goes to show that the specific metal and how it has been treated makes a pretty significant difference in the way it ages.  Now lets take a look at how we can conceptualize this in 3D...

 
 

This is basically how I think of it in my head...

    First thing you need to do is figure out what you're trying to do.  I know that sounds redundant, but I think a lot of people skip this step.  If you don't conceptualize it, you won't know where to go and will probably just end up wasting a lot of time fiddling around with different ideas that may or may not really work.  Now don't get me wrong here, I think that fiddling around with different ideas may work well for some projects, but even then, it's also not a bad idea to start off with something specific, and then branch off from there.  At any rate, notice a few things about this thought process.  For one, I'm conceptualizing everything into layers.  That's because texturing in 3D works by layering things on top of one another like this, and it's also easier to break down something complex when you think of it in layers.  Next, I'm starting to think about the specific channels I'm going to be working with ahead of time.  I try to associate things like surface relief to the elements that cause them.  So, rather than placing my bump/normal in the base metal, I'll modify it when I get to the heavy rust.  So now lets get more specific.  Lets ignore the light rust for now and take a look at everything you need to represent the heavy rust sitting on top of the base metal...

 

 
 

These are the bitmaps you would need to fully represent the heavy rust sitting on top of the base metal

    So now you might see why it's really temping to just throw on the base metal with a few sliders and call it a day.  The fact is, creating all of these bitmaps can take time, and it's not really easy to get all this information correct in one shot.  If you don't get one of those maps correct in the first try, there's probably going to be a lot of back-and-fourth between fixing stuff and getting things right, and that takes time... sometimes a lot of time.   Plus, this is only one layer of grunge.  In this scenario, we're not accounting for the lighter rust, any other sort of weathering, or ways of blending multiple layers together.  In short, this is when things can start getting pretty complicated.  Or... in the very least, feel complicated.  Think back to the first layered diagram I drew out.  This is why it's really important to think about the elements you want to make ahead of time.  When things start feeling really complicated, you can just think back to the basic plan of one layer sitting on top of the next.  As long as you keep that layered material concept in mind, you'll be able to figure out what to do next if you get stuck.  As far as software and workflows go, I think talking about that can be an entire blog or three within itself.  There's probably 50 different ways you can go about making these bitmaps these days with pros and cons to each approach.  But, in short, I believe substance designer/painter is the best out there right now when it comes to managing heavy amounts of complexity while maintaining a fast workflow when it comes down to it (And by the way, I'm not sponsored by allegorithmic).

    So there you have it!  Next time you're looking at metals, try thinking about some of this stuff as you're shading/texturing.  Aged metals can be really fun to shade, and applying a bit of thought behind the weathering process can really take things to the next level if you haven't incorporated these elements yet.  Also, be sure to keep an eye out for a tutorial series that I made called, "Modo Texturing and Shading Fundamentals" at pluralsight.com  Even if you're not totally interested in learning Modo, I go over a lot of texturing/shading theory and methodology.

 

Till next time, thanks for stopping by!

 

-  Tyler