Creating texture images for metal plating

Colin Litster has a great example of how to create a copper plated roof in his book Blender 2.5 Materials and Textures Cookbook. The the image files of the are available from the publishers website, naturally they are copyright protected, which reduces their usefulness greatly. Furthermore the book gives good details on how to apply the images as textures in Blender, but the information on how to obtain/create the base image is sparse to non existent. Searching the web did not result in any image that would be usable. Therefore I set out to create the images from scratch.

For the recipe there are three images needed:

  1. Base image used as a color map in grey scale. This image is tileable (plate boundaries wrap around the sides)
  2. Bump map based on the base image. The basic idea is that the plating is thicker where two plates lay on top of each other
  3. Specular map. Especially for freshly polished copper there is specularity.  Since I intend to use these textures for oxidized copper the specularity is not that intense.

Creating the plates

Before starting to create the plates I find it advisable to think about how the real thing is manufactured: I guess the bottom plates are the first to be placed, for the arguments sake lets also assume that they are placed from left to right. This results therein that plates placed to the top hide the top part of underlying plates. This means that we should start the drawing at the top left and work through the bottom right. For modelling I decided to use MyPaint over Gimp.

overlapping metal plates produced with myPaint

This is the result. It clearly visible how the plates the the right should cover parts of their left neighbours. The first steps in Gimp therefore is to remove the undesired lines. I resized the image as well as shrunk the lines. When shrinking them make sure that you prolong the lines to touch the borders.

Texturing the plates

The texturing of the plates is done in several layers. Larger details are placed at the bottom of the stack. The lowest level has a basic light grey. On top of that the plate outline is layered.  Then I put in a blend layer. For each plate there is a blend from a light grey to a darker grey, mostly from top to bottom. such a blend is done by selecting the plate (with the wand tool on the plate layer) and then adding the blend on the blend layer. The whole blend layer has an opacity of about two thirds.

The next couple of layers are grey diff to add some individuality to the plates. This is done by selecting all the plates that are to be defined on the active layer and use one brush with different sizes and grey values. All plates on a layer use the same brush. Each tile is only painted in one of these layers.

On top of that I added another grey diff layer but this time over all plates using the same technique as above, but with less detail.

Next comes a layer that defines some specular highlights. I used different brushes in a lighter grey than the base color. On top of that I added a stain layer depicting light (mostly) horizontal lines.

cupper nail headThe top most layers adds the nails holding the plates in place. For that I created a brush from a copper nail head, that I turned into a grey scale image and removed the background. With that brush you can stamp on where you want the nails. Though they are all oriented the same way. I therefore selected each nail individually, rotated it and anchored the layer. Additionally you might want the resize the nails. The brush is stored in the zip file at the end of the article. Add it to your gimp directory in the brushes folder and hit reload on the brush panel.

This is the result:

copper plating greycolour


Bump and specular map

The bump map can be squeezed into the gimp file, directly above the plate layer. Once again select the plates and resize the selection. How much is dependent on the line width dividing two plates. In my case 3 pixel did the trick. This is needed because you want to hide the dividing lines and there should not be any gaps. Special care must be taken with the plates on the border. Plates at the left and right border should be selected together so the same blend is applied the both parts (they belong to the same plate since the image is tiled). The ones at the top and bottom are a bit trickier, since the blend starts at the bottom of the image and then proceeds with the lower part of the plate which is located at the top of the image. The blend is from white to black. Since the top of the plate is hidden the blend should start where you guess the top of the plate would be:

copper plating bump map

For the specular map I used the merged model (without the bump layer) as a base. Then I added a copy on three layers. On the bottom I Posterized the image with three colours. In the layers above I did the same with 7 colours to re-add more detail. The top layer has increased contrast. The top two layers only have opacity of 50%.

copper plating specular map

I’m not entirely satisfied with the result, but that is the best I could do. If anyone knows how to produce better results with the available material, please let me know.

Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

All the resources are packed in this zip.

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