Smashin'... Metal
Applying damage to metallic surfaces.
Introduction
This article is a showcase of different kind of damages on metal surfaces, from a texturing point of view.
(Note: I use Modo and PaintShopPro, but I think the workflow is pretty similar when using other 3D/2D applications.)
The victim
This is our base metal plate. I chose copper because it is one of the softer metals, so outside forces leave more distinct marks.
Hammer
Now let's see the effect of a heavy, blunt object. A hammer for example leaves rounded rectangle indents. Usually one corner or one side is deeper, because the hammer head arrives at the surface with an angle. Also there are brighter spots of wear: the darker copper-oxide layer was brushed off here and there.
To make the bump map first make like two slightly different hammer hits: one is deeper at the corner one is at one side.
Then mix them together by randomly rotating them on top of each other. There are a few plugins which make this work easier by randomly scattering around images on the canvas. Here I just pasted the hitmarks as layers a few times, and manually rotated and moved them. All layers had the "multiply" blendingmode.
In modo, the brighter, brushed spot is made by a group inside the main copper material. It contains the copper texture with the "add" blending mode and a group mask using the image on the left. It's a rock kinda texture, made by FilterForge, but other noise texture should work as well.
Impact Hammer
The good old UnrealTournament weapon... :) It makes round marks on the player's bodyarmor. Pretty much the same as the hammer, only the shape is different.
The round gradient was made in FilterForge as well. It is not linear, but has a profile of an arc. The linear gradient (default in most 2D applications) would result in a cone shaped indentation.
The brighter spot is also similar to the previous one, but the style of the noise is more organic and rounded.
Ice crusher
Ms. Tramell's favourite household item would damage the surface like this. This assusmes that this plate is not solid but was pressed out of a 2-4 mm thick sheet of copper. On a thicker structure the pointy tool would leave less visible holes. I think a PB gun would also have this kind of effect.
You know the drill. This time the gardient's curve is spike shaped. I also varied the opacity and size of the elements, so the depth/radius of them are not constant.
The scratches were made with MapZone Free, a very nice photoshop plugin (It also works with Paint Shop Pro.) It has a preset called "Ice".
Of course you can achieve this texture using other methods.
If you apply the texture as a bump map then you'll have the surface cut by swords or other sharp tools. It should also work on wood materials as well.
General scratches
Small scratches everywhere, caused by years of usage of the object.
The bump map is based on photos of scratched metals. It is usually easy to separate the wear from the intact parts of the metal, as they usually have different color and/or lightness. On CGTextures.com there are a many very useful photos, and this subject even has a separate section.
Combined
Usually you won't use the forementioned effects alone, but combined together. Let's see an example here: all four kind of damage is present for a certain degree.
Rocket blast
When an anti-vehicle rocket (bazooka) explodes on the thick armor of a bunker, it leaves a crater similar to this. The metal is usually flexible enough and won't crack (like plain concrete), but the explosion certainly bites out a big portion of the surface, and turns them into shrapnels.
The radial structure of the texture is based on the "lensflare" filter, with only the rays left visible. A heavy gaussian blur helps to smooth out the streaks.
For the smoke streaks I used the radial blur on a noisy layer. I cleared the center to indicate that it was so hot, even the grime has evaporated.
Acid
Alien saliva vs. copper. While the acid eats itself into the metal, it produces heat and different gases, which makes the liquid to boil. The textures roundish, cell like pattern reflects that. The greenish part is residual copper-oxide, accumulated at the edge of thebubbles and the poddle.
The contours of the splashing acid was made by one of my FilterForge filters.
The filler is a cellular noise, also made in FForge, but it can also be done in modo's cellular procedural.
I used the "Find all edges" function to make a mask for the oxidized area.
Scraping off paint
Now move on to a painted steel plate, and let's start removing the paint.
Here you can see our second victim. It's not brand new, but in good shape. For now.
General scratches
General wear of the material.
The mask of the paint layer is based on a photo. Or actually two of them, on top of each other, so the effect is much more pronounced.
A different look can be achieved by using a crumpled paper as the source of the scrathes.
First, clean up the image by aggressively removing the noise. I used "edge preserving smooth". After this "trace all edges", which would give you an image similar to the one showed on the left.
The "dilate" command makes the lines more pronounced. Adjust the contrast and brightness of the image and apply a bloom as a final touch.
Pronounced damage
Sometimes we need much more harsh damage to the surface. I experimented with 100% procedural methods, but I soon realized that it's way better if I actually damage stuff in real life. I took a thick cardboard, painted dark and started to hurt it with different tools: screwdriver, hammer, rasp, sandpaper, you name it.
And this is the result.
To add depth to the carvings, I derived this map from the previous one. Several "erode" operation contracts the shapes on the image, but also introduce square artifacts. To make them less visible I applied a texture based distorsion.
Burned paint
Let's use a blowtorch. First the paint burns, it turns black and becomes rigid. The heat induced gases push the paint up, away from the surface, thus making small bubbles. Towards the edge the paint layer had no direct contact with the flames, only the radiating heat caused bumpiness.
The bump map was made with MapZone Free, with the "cosmos" preset. It's basically a bunch of gradient spots, with different sizes and opacity.
To show the effect of the blowing flames, I applied a mild radial blur. "Add noise" and "Edge preserving smooth" gave it the final look.
That's all for now, I hope you found it useful.