How to create an image like the one below.
I started with a 600x600 image, for larger/smaller sizes, adjust the various effects settings accordingly. You will want to have a default white background, and maybe a patterned background and possibly a black background, each on its own layer so as to test how your bubble looks. Different backgrounds require different settings on the highlight and shadow layers.
1. Start with a new transparent layer. Do Filters>Render>Clouds>Plasma. Jack the turbulence up to around 1.7 - 2. If you don't like the colors, click "New Seed". Blur the plasma by about 7-15 pixels, depending on how turbulent you made it. This is an area for experimentation.
2. Now, do Filters>Distorts>Iwarp. Boost the deform radius up to around 70 or so. Use a combination the various available functions (move, swirl, grow, shrink) to mix up the plasma. Not too much, but enough to make it look like the swirly iridescence on the surface of a soap bubble. When you have something that looks good, click okay.
3. Set the layer opacity at around 35-40.
4. Now, we need to make the colors a bit more intense, since the previous step kind of washed things out. To do this, do Layers>Colors>Levels. You will most likely want to move the two endmost sliders in toward the middle. Experiment with all three sliders. I can't give you any specific values due to the random nature of the plasma, it is best not to get too carried away however (in the examples for this tute I kinda overdid the levels). There is also a scrip-fu called "Vivid Colors" which might give interesting results, but I haven't tried that. Might be worth looking into.
5. Duplicate the color layer. On each color layer, do Filters>Map>Map Object. Make sure you have transparent background checked. Go into the Lighting tab and select "No light". On the second layer, when you do map object, change some settings in the "rotation" section of the orientation tab. This second, rotated layer will give more of a feeling of depth to the bubble.
6. Okay, now you have two transparent spheres, one on top of the other. From here, you may have to mess with the levels again as well as the transparency settings, especially depending on what background you use for your bubble. If you want, name the two layers "color 1" and "color 2".
7. Create a new transparent layer at the top of the layer stack. We will be using this selection in conjunction with others to help make the various highlights and shadows on our bubble. On your topmost bubble layer do Layer>Transparency>Alpha to Selection. You should get a selection exactly surrounding your bubble. Save this selection to a channel. Name it "whole bubble". Keep the selection. Do selection to path.
8. Shrink the selection by 5-6 pixels. Turn on quickmask by clicking the little icon down in the lower. Do Filters>Blur>Gaussian Blur. Blur by about 20 pixels. Turn off quickmask by clicking the icon again. Save the selection to a channel.
9. Go to your channels tab and pick the channel with your original "whole bubble" selection, right click on it and do Channel to Selection. Now pick the channel with the selection you just blurred with the quickmask and do Subtract from selection. You will now have a "donut" shaped selection. You can't see it, but the outside of the selection is crisp, while the inside of the selection is blurred. We will be using this technique several times in this tutorial. There are two reasons for this. One, it lets us control where the blurriness in the selection occurs, plus, it allows us to blur the highlights before we fill them. If you notice, when you try to blur a white highlight on a transparent background it tends to go "muddy". This way we get a nice blur, but without the muddy.
(Edit: The bubbles with the selecitons are backwards in the two screenshots below...I will fix this later, but you start with the larger, then subract the smaller...)
10. Select the transparent layer you created in step 7. Bucket fill the ring shaped selection with white. Cancel the selection. Set the layer opacity to 35-40, we can tweak it later. Now, you might ask..."Why are we doing this narrow selection like this? Why not just stroke it with a white fuzzy brush?" Because the fuzzy brush has only so much fuzziness and if you need more, blurring white on a transparent background tends to make it go "muddy". Name this layer "outer rim".
11. Create a new transparent layer just above the color layers and below the "outer rim" layer. Select the 7x7 fuzzy circle brush. Make sure you don't have any active selections. Go to your paths tab and right click on the path you made in step 7. Stroke the path with the brush tool. (I don't show this step in the pics...) You will get a fuzzy outline around the perimeter of your bubble, it will go partway outside the bubble, don't worry, we will take care of that in a minute. We don't have any problem blurring black, select the layer you stroked the path on and blur by 7-10 pixels. Then go to your channels tab and pick the "whole bubble" selection and do channel to selection. Go back the layer with the stroked path. Invert the selection and do Edit>cut. This will trim the excess blur from around the outside of the bubble. Adjust the layer opacity to give a nice modelled effect to your bubble. I set mine at 44.
13. Create a new transparent layer at the top of the layer stack. Drag out a vertical guide from the left edge of your canvas, place it at 300. Using your elliptical selection tool, put your cursor on the guide a scant 1/4 of the diameter of your bubble from the top edge. Start to drag out a selection, but press your
14. Make sure you have white as your foreground color. With your gradient tool set to a foreground to transparent gradient, put your cursor just above the selection and drag down a gradient to fill the selection. Stop just a bit before you reach the end of the selection (like in the image above). If the highlight you just created looks good, cancel the selection. Otherwise do Edit>Clear or hit
15. Now...you can leave your highlight where it is, or you can use the rotate tool to rotate the layer and put it wherever you want. In most of the ones I posted to the gallery, I rotated the whole highlight layer by about 45 degrees...kinda diagonal from the accent highlight. In fact the two of them should probably be opposite each other (which they aren't in this tute...I was too lazy to rotate my highlight layer...sufferin' from screenshot burnout...)
16. Now we need to create an accent highlight. Go to your channels tab and pick the saved selection for the whole bubble. Create a new transparent layer on top of the layer stack. Pick your move tool. Make sure you click the icon for moving selections rather than layers and move your selection as shown in the picture. Save this newly moved selection to a channel.
17. Pick your original whole bubble selection from the channels tab and do Channel to Selection. Now pick the channel with the moved selection and do Subtract from Selection. You should have a nice crescent shaped selection at the edge of your bubble.
18. Turn on quickmask. Do Filters>Blur>Gaussian Blur. This is kind of an eyeball sort of a thing, but look at how blurred the mask is and imagine that as the highlight at the edge of the bubble. I used a value of 30. Turn quickmask off and save the resulting selection to a channel.
19. Bucket fill the selection with white. Shown here with a black background for clarity purposes.
20. Pick your original whole bubble selection. By now you should be familiar with how this works. Select the highlight layer you just created. Do Select>Invert and Edit>cut. This will trim off the excess blur from the outside of the bubble. Tweak the layer opacity to an amount that looks good. I used 38.
21. Now for a drop shadow. Basically these steps are the same as we used to create the white "outer rim" highlight, but with a thicker donut selection and with black as a fill color.
Create a new transparent layer, JUST BELOW the color layers in the bubble. Go to your channels tab, pick your whole bubble channel and do Channel to Selection. Shrink the selection by 25-30 pixels. Turn on quickmask. Blur your quickmask by 75-80 pixels. Turn off quickmask. Save the blurred selection to a channel. Name it "inside drop shadow".
22. Pick your whole bubble channel and do Channel to Selection. Now pick the blurred selection you just created and do Subtract from Selection. You will get a large donut shaped selection with a sharp outside and a blurred inside.
23. Pick the transparent layer you made below your color layers. Bucket fill the selection with black and cancel the selection. Blur the resulting black donut some more...5-10 pixels worth. Now set the layer opacity down low, around 25 or so. From here you can move the layer around to position the shadow where you want. You can also use the perspective tool if you are going to create a 3D sort of background, then move the shadow layer. Remember if you move the layer to do Layer>Layer to Image Size.
Edit: User LIMN has taken the time to make a script-fu for the above. The link is http://www.mediafire.com/?9edqgcdzvwt.