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Noting that some have referred to it as the "Scott Effect," and pleased that there is a little interest in it, I remembered my promise to Alexey some months ago to write a tutorial. Here it is, Alexey - better late than never!

Introduction. The effect is useful for realistic rendering of irregular and corrupted surfaces. It is based on the observation that rust and corrosion, for example, begin at random "nucleation" sites and propagate in a random fashion. To simulate this process digitally, I have explored the idea of selective removal of portions of a randomly generated plasma field (Filters - Render - Clouds - Plasma) using Select by Color. In this tutorial, we develop an example that illustrates the technique in its most basic form. My result is shown in the figure on the left. The technique is not a cookbook at all in that you will never be able to exactly reproduce the same result twice. This is because of the random nature of the plasma produced by Gimp. Also, results will vary, depending on the object to which you choose to apply the effect. Thus every creation is truly unique. Further, almost endless, elaboration of the basic technique described here is certainly possible. Although I have used the effect largely to produce rust, corrosion, peeling paint and the like, I indicate below some applications and other uses including, suprisingly, the rendition of wood.

1. To begin, create a shape whose surface is to be textured. Any shape or color will work. For simplicity I have chosen an anomalous artifact, a remnant of a crashed flying saucer, circa 4000 BC, unearthed in the ancient Middle East. Any other simple shape, a ring or rectangular frame for example, is fine for the demonstration. Place your shape on a transparent layer over a dark or black background layer as in the figure.

2. Next, use Apply Alpha to Selection to select the shape. Then, create a transparent New Layer above your object. With the selection still on, apply Filters-Render-Clouds-Plasma set to, say, 2.5. Put the New Layer #2 in Overlay Mode and remove the selection.

3. In the next step, we will selectively remove portions of the plasma layer leaving others intact. This is the key step: it will allow us to utilize the random nature of the plasma to create realistic looking surface effects. To begin, simply desaturate the plasma. With the plasma layer activated, use Image-Colors-Hue-Desaturate. Next, make the layer with your object, New Layer, and the Background Layer invisible so as to more easily view the plasma layer, New Layer#2. With New layer#2 activated, use Select By Color, holding the Shift key down, and click around in the plasma, selecting areas or patches to be cut out. Use your own intuition, artist! When you have selected some areas your display should resemble the illustration on the left. Then, just use Edit-Cut to remove the selected portions. With all layers but the plasma still invisible, you should now have achieved a holy (but not sacred!) plasma layer looking something like that in the illustration on the right.

4. With your object, plasma layer and background layers switched back on, duplicate the holy plasma layer, New Layer#2. Then turn New Layer#2 off for now. Next, apply Filters-Map-Bump Map to the duplicate, New Layer#3, with Bump Map set to Invert Bump Map and a depth of 3 to 7. For a map, be sure to use New Layer#3 itself. It is easy to over do this. Experiment, but I used Linear mapping here. You may or may not choose to use Compensate for Darkening, depending on your artistic sensibilities, but mostly on how dark your plasma is! Your effort should now look something like the illustration on the left, with the bump mapped layer interacting with the object layer through the Overlay mode.

5. Now, make visible New Layer#2, the holy but un-bump mapped plasma. Here we can play with the different Mode settings and Opacity for the two layers, New Layer#2 and New Layer#3. Try, for example setting New Layer#3 to Mode Overlay and investigating the effect of setting New Layer#2 in the various other modes, adjusting opacity as necessary, looking for something you like. Best results are often with New Layer#3 in Overlay, but this is not always so. Again, what works well in one case may not in another due to the randomly generated plasma layer you start with and the nature of the object over which you overlay it. I got tired at a point shown in the illustrations above. My particular settings were New Layer#2: Hue and New Layer#3: Darken Only (which has an Overlay-like property). You can now tweak up color and contrast as you like. Finally, I put my object over a colored background I liked and added a drop shadow, as shown in the illustration accompanying the Introduction.

Remarks. I have experimented with the effect in creating such things as interfaces. I am working on good renditions of brick, especially, and of stone. Beginning with a sheet of corrosion, I created the floating letters in the illustration on the left. And the effect is not confined to rust: I have also used it to make wood, such as that shown in the illustration on the left, and the wood-like objects that appear in several of the images in my GUG gallery.