Picking cabbage nails turn black can be cleaned with soapy water, alcohol, etc., or cut off part of the nail.
Picking cabbage nails black is due to the process of picking cabbage, nails stuck to the cabbage in the chlorophyll, encountered air oxidation turned black. You can immediately use water to rinse, or use soap and water, alcohol, etc., on the black parts of the nails to wash, dissolve the residual chlorophyll on the nails.
If part of the chlorophyll residue is more stubborn, you can cut off the part of the nail that is stained by the juice of the cabbage, but you should avoid excessive pruning.
Normally, when picking cabbages or other vegetables, you can wear food-grade gloves for the operation to prevent blackening of the nails.