Chullin 88 - Materials for Covering the Animal Blood
If blood from animal slaughter became mixed with water and the amount of water is such that the mixture still looks like blood, one has to cover it. If blood mixed with red wine, then we look at wine as if it were water. If the corresponding amount of water in the mixture would not make it loose its appearance of blood, one still has to cover it. The same is true if it mixed with some other blood that does not require covering, such as blood of a domestic animal, but Rabbi Yehudah argues and says that blood cannot nullify other blood, and one always has to cover the mixture.
Blood that splattered - the Sages say that it too has to be covered, but Rabbi Yehudah says that covering any part of it is enough. All derive their opinion from the words in the Torah "its blood" but interpret them differently.
One may cover blood with fine sand or dung, lime or ground pottery, but not with course sand or dung, nor with uncrushed bricks. Rabban Shimon ben Gamliel stated a rule: "Blood can be covered with anything in which plans can grow."
Art: Francisco De Zurbaran - Still-Life with Pottery Jars