1 - Plain, 2 - Plain (reduced), 3 - Over Clear, 4 - w/ Silver Leaf, 5 - w/ Silver Leaf (reduced & encased), 6 - w/ Silver Glass Frit (reduced), 7 - w/ TerraNova2 Frit, 8 & 9 - w/ Tuxedo, Copper Green, Opal Yellow, Ivory, Peace
Effetre Oliva Nera is an extremely dark, saturated transparent brown. It's so dense, then when used as a solid colour, and even when used over a core of clear, it looks black. It is maybe a little on the pink side of brown, which you can't really see until you put it over something light like Ivory or White. This colour melts beautifully, being of average viscosity. It is not especially prone to boiling, and it is fantastic with silver and silver glass. The best news? It's pretty cheap, too.
When silver leaf is melted onto the surface of Oliva Nera, it develops into a crust on the surface, and a blueish iridescence develops around its edges. When the leaf is reduced and encased, it looks like a greyish, faintly shiny coating under the clear that has purplish blueish tinges to it.
On top of Oliva Nera, my reducing silver glass got very shiny and developed very nice colours. The TerraNova2 frit was also surprisingly nice (for me) so I am going to surmise that Oliva Nera is sort of a universally nice silver glass base colour.
Oliva Nera is not very reactive with any of the other colours I tested it with. (please excuse the dust in this picture - I should take another one, but I don't really feel like it)
The only reactions visible are a slight separation of all of the colours (apart from Tuxedo) that I used on top of it, and then some spiky bleeding into Ivory in the bead on the right.
Here's a fun bead with Oliva Nera. I really like this colour.