We now have little bluish-purple dots covering the entire image. We could make the black areas transparent or change the merge mode to allow us to see the underneath layers, but wouldn’t it be great if we could have the dots appear only in the solid black areas outside the scalloped frame?

Editing the transparency of the gradient will not accomplish this, nor will changing the merge mode or layer transparency. What we need to do is create a Mask for this layer that has the same shape as the scalloped edge in the Box Trap layer.

Go to the Layers tab of the Fractal Properties tool window.

Click on the Box Trap layer and then click the Add layer button.

This adds the new layer between the Box Trap and Gaussian Integer layer.

• Rename this layer Mask.

But it is not a mask layer yet until we associate it with the Gaussian Integer layer.

To turn the layer into a mask, click the Use as Mask button.

Look at your image and notice how the dots no longer appear inside the scalloped frame (except on the box trap structure inside, which we will fix in a minute).

Also notice on the layer list that the Gaussian Integer and Mask layers now share a Visible icon. If you shift-click this icon to toggle the other layers off, you will clearly see which areas are visible and which are made transparent by the mask layer.