Well I thought I would start this off as so many people were having trouble with the metallic black and can tell you what I did..
For the Effetre Periwinkle blue and metallic black spiral below.. To get the metallic to come out, I turned my propane way down but still had a small flame. I gently bathed the black in the tip of the flame slowely avoiding boiling.. It has an oil slick look to it.. Kind reminds me of the surface of silver plum without being purple.
For the saffron metallic black bead below.. I made the entire bead first, pressed it, etc, working high in the flame.. When I was ready to bring out the metallic black, I kept the flame the same but brought it down in the flame until the black started boiling. The black boiled long before the saffron got too hot.. The picture makes it look like it has a rough surface but it is smooth. It reminds me of Reichenbach's Opal Black color which when reduced kind has a similar effect, at least mine did.
