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 Paint Shop Pro, 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 hit marks as layers a few times, and manually rotated and moved them. All layers had the multiply blending mode.



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 like texture, made by FilterForge, but other noise texture could work as well.

Impact hammer

The good old UnrealTournament weapon… It makes round marks on the player’s body armor. 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 favorite household item would damage the surface like this. This assumes 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 gradient’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 handy photoshop plugin (It also works with Paint Shop Pro.) It has a preset called “Ice".

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.
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 aforementioned effects alone, but combined together. Let’s see an example here: all four kind of damage is present for a certain degree.

Rocket blast

The first image is the bump map. 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 the bubbles and the puddle.

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 scratches.
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 first image.
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.
The first image 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 distortion.

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.