Creating Sparkle on Image through GIMP Photo Editor

1. Open up any image that you want sparkle on. That could be text, a photo or something else.
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3. I'm using a cocktail glass photo in this tutorial.
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6. To create the sparke we'll need a special brush that has to be created by ourselfes.
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   Open the brush dialog: Window / Dockable Dialogs / Brushes or simply press SHIFT+CTRL+B.
   
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10. Click "New Brush" at the bottom of the dialog - name it "Glitter".
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12. As FORM use the third option.
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14. The radius depends on the size of object you want the glitter to be on.
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16. I use ~75 - thats a good value for most objects.
17. Use the values of the screenshot below:
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19. SPACING is not important for us in this case because we only apply a single sparkle at a time.
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22. Now choose the paintbrush tool. The "Glitter" brush should be active automatically. If not please choose it from the dropdown where you can assign the brush.
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24. - Create a new transparent layer. Press at different places in the picture preferably at bright/highlighted areas.
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26. Tip: While applying the glitter also change the size of the brush using the brush scale option in the tool prerferences. You'll get a more appealing look if the sparkle is not always the same size.
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28. You can apply that sparkle to almost everything. Please don't use too much of it or you'll lose the effect!
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31. Tip #2: If you want to refine the sparkle effect: 
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33. - Duplicate the layer with the sparkle
34. - Set layers mode of the duplicate to "soft edges"
35. - Move the duplicate below the original sparkle layer. After that the sparkle is shining a bit more.