Onyx is an amazing smoky black, and is more opaque for designs such as colour blocking. Build in thinner layers to ensure it is cured fully.
A 30g tube of Gelic will create around 11-15 sets dependant on shape/length etc. Cure for 60 seconds in a LED lamp and 2 minutes in UV. Soak off but file off is advised as it's so easy to file and means you are not wasting acetone. Always squeeze the tube from the top and use a squeezer.