This nail powder is a black mirror one from Beauty Big Bang. You get 0.5g of powder, which doesn't sound much but you get enough for a fair few applications. Comes in a little twist lid tub sealed with a cardboard stopper. It comes with a sponge tip applicator in a small resealable pouch along with the twist lid pot of powder.
The idea is you paint your nails and use a UV / Gel topcoat, it has to be one which leaves a tacky residue once 'cured' under the UV / Gel light. Once the topcoat is cured you use the applicator to apply some product, dabbing at first and then rubbing the product in to the nail to create a beautiful mirror shine surface on the nails.
And here is a quick video demonstration of me using the powder;
I have a 10% off code "ERA10" which you can use on the website if you would like.
Black Mirror Nail Powder