I use the metallic thread in the bobbin and on the top.

when I make Fsl designs, I always use same thread in bobbin than on the top.
Hugs. Céline From France

I also use metallic thread on the bottom, but I reduce the speed of sewing to the lowest speed.

When embroidering free-standing lace, always use the same metallic thread in the bobbin as well. Once I wanted to see what the difference was and used the normal bobbin thread. Well, the result was ugly! Just be sure to use a soft metallic thread, like Robison-Anton which never needs to be put in the freezer to become soft, and gives a beautiful result.

I use the closest matching normal thread I have, my machine does not like metallic in the bobbin :(

Metallic Thread.

I use the metallic thread for both the top and bobbin threads.
I use a size 80/12 Metallic needle.
Sometimes I have to adjust my top thread tension down just a bit.
I do slow my machine speed down a bit too.

EastWitch2

Same answer as most - always use the metallic in the bobbin - it just sews better and gives a better appearance. Robison-Anton is my favorite, but limited availability. Madeira is second and more readily available and has lot more colors. Have not had great success with Sulky, but will use it in a pinch.

Sandra, I see you have the anosers - but I always use the same thread in the bobbin as I do the top for all FSL work.