Does what it says on the tin, but do read on and find out why you should be careful.
The product comes in a small pack with suitable instructions inside. These tell you that you will need to use 500g of salt and also requires the use of washing up gloves. If you look at other reviews you will also need a washing machine that is free of limescale as this can cause the dye to stick to the lime scale and cause discolouration in the future.
Be careful when opening the box as it can still have dye powder on the bag containing the dye. I stuck with the recommended instructions and managed to dye a heavy winter jacket. You can avoid needing to use gloves by snipping open the bag in the drum and emptying it out inside, then on top of that goes the 500g of table salt. Wash it on a regular cycle and then wash it with detergent. The instructions told me to wash the drum out with detergent after, but I didn't bother. There was a slight puddle of black dye on the rubber seals which go around the door and on the clear window but was quickly dispatched with a damp jay cloth. I put in some dark clothes afterwards and all of which have no black marks.