Washing maschine or by hand? Youre choice. I would recommend washing maschine
How many pieces? You can colour clothes up to 1 kilo in your washing maschine, wet them before you start and put them on a weight.
What kind of clothes? You have to check out what kind of material the clothes are made of. This Nitor colour is specially made for cotton. Start with a few pieces- and don`t colour your silk dress!!!