This filter adds a glowing hot metal effect to the alpha (that is to these areas of the active layer defined by the non-transparent pixels).

The filter is derived from the “Glowing Hot” script (File → Create → Logos → Glowing Hot in the image window), which creates a glowing text logo (see above).

The filter simulates a red-hot, a yellow-hot, and a white-hot area - each color representing a different metal temperature -; the alpha's outline shines through the glowing.

This filter is found in the image window menu under Filters → Alpha to Logo → Glowing Hot.

The filter only works if the active layer has an alpha channel. Otherwise, the menu entry is insensitive and grayed out.

To create the glowing effect (red-hot, yellow-hot, and white-hot area), the alpha is feathered and then filled with the respective color, from red to white with decreasing feather sizes and color intensities in the feathered area.

The illustration below shows the “hot metal” colors and the width of the feathering border in percent of “Effect size” (these are the values the filter actually uses).

In the example images you can see how the alpha's outline shines through the glowing. This is achieved with a alpha filled with black as top layer, where the layer mode is set to overlay. Using a black overlay layer won't change pure white, but darkens light colors at the alpha's edges so that the outline appears.