Woman in niddah state standing on elevator rug using her full body weight, thereby rendering the rug a "midras tmeiah" (unpure midras)
Midras uncleanness (Hebrew: טומאת מדרס) is one of the forms of ritual impurity in Judaism which can be transmitted by either an object or person. The term may be translated as pressure uncleanness.[1]
A midras (lit. "trampled on" object) is an object that can be a carrier of ritual impurity. Common objects that could potentially become unclean, and become a such midras object, include a chair, sofa, mattress, and rug. A person who becomes unclean is categorized as a "father of uncleanliness".
A niddah hut (Mergem Gogo) at the Jewish village of Ambober in northern Ethiopia, 1976. Beta Israeli women left their homes and stayed at the hut during menstruation, until they could immerse at the river and return home.
Hebrew Bible
The general concept of a midras, an object becoming a carrier for uncleanliness, is brought in the book of Leviticus, though the following verse does not employ the Hebrew term midras;
Anyone who touches his bed must wash their clothes and bathe with water, and they will be unclean till evening.
According to Maimonides on Zavim 4:4, the midras object becomes unclean by a person who is a "father of uncleanliness" (such as a man with a seminal emission or a woman in the middle of menstruation) putting most of their body weight in one (or more) of five ways on the midras;
sitting on the midras like a chair
lying on the midras like a rug
leaning on the midras
standing on the midras like a mat
hanging from the midras
Transmitting uncleanliness
Once the midras becomes unclean, it transmits uncleanliness to clean persons or objects by one of seven ways;
by touching the midras
by carrying the midras
by sitting on the midras
by lying on the midras
by leaning on the midras
by standing on the midras
by hanging from the midras
The person or object who becomes unclean via the midras is categorized as a Rishon L'Tumah.
Purification
The purification of the midras object is accomplished by immersing the object in a mikveh bath (before sunset), and the subsequent elapse of sunset.
Disqualified objects
Objects that are not subject to becoming unclean as midras include;
Fabric or vessels made from fish (or any sea-life)
Objects or vessels affixed to the ground
References
^Jacob Neusner (2005). Is Scripture the origin of the Halakhah?. p. 141. The pertinent classification of uncleanness called Midras- or pressure-uncleanness pertains only to objects that ordinarily are used to bear weight or pressure, that is, beds and chairs and things analogous to them
