How to marble items using nail polish
Put water into the container. It will get a bit scummy so an old ice cream container is probably better than your best casserole dish.
Pour in some nail polish into the water, then quickly dip your item into the nail polish swirl. You need to move fast.
Let item dry, ideally without touching the nail polish. It will dry quickly.
If you need to swirl again on a larger item, or add another colour, repeat. Watch the water isn't too 'scummy' as it'll ruin the next dip.
The height of water will depend on the size of the item being marbled.
You can part dip, roll on the surface or other techniques. It just needs a bit of practice.
The water will get a kind of scum layer on it from the polish, so if you're marbling a few things, you'll need to regularly change the water.