Here is a complete guide to creating customized repeating patterns in GIMP and then adding and using them from the Patterns library.

How to Make a Filled Selection With GIMP. GIMP, a free image-editing tool, comes with a variety of useful brushes, filters and tools that allow you to create professional looking business graphics ...

Although GIMP does not include a diamond texture option, as of June 2012, experiment with digital patterns, paint brushes and filters to superimpose a sparkling effect.