If you think your piece will require washing or wet blocking when completed, it is advisable to test all threads before stitching. Submerge thread thoroughly in tepid water and put on a white paper towel. If the thread color bleeds, continue to flush it thoroughly until the water runs clear. Allow the thread to dry completely before stitching. The heat can reactivate the dyes and cause bleeding.
Many metallic threads have a highly reflective sparkly surface.
Because these threads reflect so much light they may obscure the detail of some stitches. A complicated stitch might not be appreciated if executed in a metallic with lots of shine. Choose simpler stitches that will show off these dynamic threads, rather than compete with them. Metallic Chainette threads have a soft feel because of the way they are made. But if you catch the end just right they will unravel rather quickly.