I cut an onion with a meat knife on a meat cutting board. The next morning, I found a dairy knife on the cutting board (which hadn’t been cleaned) with some apple bits on the blade. I assume one of my children cut an apple with the dairy knife on the cutting board that still had the residue of the onion (that was cut with the meat knife) on it. What is the status of the cutting board? The dairy knife? And what if the meat knife was used again on the same board before cleaning?
The knives and cutting board are all still kosher and there is no need to do anything with them. The reason is because although it is preferable not to use a meaty cutting board for milky things. However in retrospect, we will not say that the cutting board makes the knife that was used on it meaty. The same would apply even though a milky knife was used on it, it will not render the knife meaty.