You can use your base and ultramarine purple as the only colours for making a purple, but you won't get a lot of shine. Having said this, 3 parts base with 1 part ultramarine violet makes a fantastic base colour!
The recipes you make with ultramarine purple are going to be violet toned (more blue) and quite light in colour. You can add black (black-blue iron oxide or a black mica) to make it a darker tone, more purple-y. But to really make the purples pop, you'll want to add some micas. I suggest getting a nice violet mica (see below and right) for more violet-y goodness, a deeper purple like patagonian purple, and a silver or white mica if you want to make it lighter. You can throw in some blue to make it more blue, and you can use something pink toned like oriental beige (a good example of that is here at Suds & Scents for the perfectly purple! We've done both versions and this a great recipe!) The great thing about trying the colour alone with the base is that you can go nuts trying various micas. Don't just stop at purple toned micas! Try a variety and see what you like.
DEEP VIOLET - a very basic, not shiny colour
3/8 tsp base
1/8 tsp ultramarine purple
1 scoop of blue iron oxide (optional)
Put into the baggie. Squish until you are happy (the not-mica colours are harder to incorporate, so you might have to squish a lot more than you expect). Put into containers. Rejoice.
PURPLE MIST - shiny, a lovely complement to the deep violet
3 tsp base
1/2 tsp and 2 white scoops ultramarine purple
1 scoop black-blue iron oxide
1/2 tsp patagonian purple mica
2 scoops sunpearl silver mica (or other silver you like)
1 1/2 tsp base
9 scoops ultramarine purple
1 scoop violet mica
a titch black-blue iron oxide (a titch means just a tiny bit - about 1/4 a scoop, if that!)
SUPER DUPER ULTRA SHINY VIOLET EYE SHEEN!
3/8 tsp base
3/8 tsp violet mica
1 scoop ultramarine purple
Tune in next week for more purple eye shadow!