Niddah 62: Seven Substances that Remove Blood

A new Mishna tells us that there are seven substances that will remove blood.  If they remove a bloodstain well, then we know that the stain is from blood rather than from another chemical.  These are saliva, liquid from split beans, urine, neuron (sodium carbonate), borit, cimolean earth (from clay) and potash (from grass).  The Mishna describes how to use these substances (including soaking in saliva for three days, etc.) and in which order to use them.  The process should be repeated three times, in the proper order, for the desired outcome to be achieved.  

Gemara commentary discerns the precise details of each of these substances, their uses, and their parts in determining whether an item is ritually impure or not.  The rabbis share arguments regarding many of these items.  One of these is where Rabbi Yochanan recalls Rabbi Chiyya's teaching that once a garment has gone through each of these cleaning techniques seven times, the garment is either still stained and so the item is ritually pure (not from menstrual blood in the first place) or it is perfectly clear and thus came from blood but that blood is gone.  In both cases, the item should be considered to be ritually pure.  Rabbi Lakish notes that this cannot be a quote from Rabbi Chiyya for his teacher was Rabbi HaNasi who wrote the Mishna and thus ruled more stringently on this matter.