Often iridised surface details are created by using iridised sheet glass and then masking and sandblasting off the unwanted portions. But you can make your own iridised surface detail much more cheaply by using pearlised mica powder.
One way to apply the mica in areas of detail is to make a stencil from stiff card and sift a smooth relatively thin layer of mica onto the area of glass you want to be iridised.
A second is to mix the mica and powdered clear glass in equal amounts and sift that onto the glass through the stencil. This can help more of the mica to stick to the surface.
A third is to sift clear powder on first and then a coat of mica. This works less well for me than the other two.
It does not matter if you put too much mica on, as the excess will not stick and can be brushed back into your container for future use. The firing should be at full fuse temperatures to allow the mica to sink into the surface of the glass. When you have poured the excess powder off you are left with an iridised surface where the mica has sunk into the glass. You can, of course, use any of the coloured micas for this purpose.