The traditional way to clean a seal is, after use, to simply stamp it over and over on to scrap paper until nothing more appears. The trouble with this method is that it leaves seal ink residue to accumulate in the grooves of the seal stone. Eventually the carving will fill with this dried leftover ink and you won’t get a clean impression. If the stone is not too soft you can use a soft cloth—old towels work well—or paper towels to wipe the leftover ink off the stone. I saw a video on the internet of someone using a toothbrush to scrub the ink off the stone under hot running water. There are two problems with this method. First is that seal ink is poisonous and shouldn’t be washed down the drain. Second is that a toothbrush may be too rough and could scratch the surface of the stone. Although I have no personal experience to verify this, I was told that some of the most beautiful and expensive stone can be so soft that merely brushing your sleeve accidentally across the seal surface can scratch the stone. One reason I don’t recommend using soapstone, rather than harder Chinese seal stones, for seal carving is that you can easily scratch this soft stone with your fingernail, and it definitely should not be cleaned with a toothbrush. Try to be aware of the hardness of your seal stones and use the appropriate method when cleaning them.
You might be able to see in the illustration above how the red seal ink is starting to build up in the grooves of the stone.