Av Melacha: Washing wool to make it white.

Principle: Removing an unwanted substance that has become part of a material.

Toldot: Dusting, wringing, or applying water to dirty material.

In practical terms, the halacha depends on the type of material and the type of dirt being treated.

A. There are two types of material:

1. Non-porous material -- e.g. glass, plastic (or plastic-laminated surfaces).

2. Porous (or semi-porous) material -- e.g. cloth or leather.

B. We can differentiate between four types of substances:

1. Non-absorbed -- e.g. feathers, hair, lint.

These may be removed from all materials, by hand. Using a brush to remove feathers or hairs is prohibited (Uvdah d'Chol). However, one may brush off feathers or hair with a brush that is used only on Shabbat ("Shabbat brush").

2. Absorbed and small -- e.g. dust, powder.

a. This may be removed from plastic and leather material by hand, with a rag, or with a "Shabbat brush."

b. A dusty water-resistant raincoat may be shaken out only lightly.

c. One may not dust, shake, or brush off cloth material by Torah law, since the dust is (partially) recessed in the cloth. However, it is permitted to lightly blow the cloth, because this will only remove the surface dust.

3. Absorbed dry stains.

a. From plastic material: this can be removed in any manner, as long as one doesn't rub the surface vigorously.

b. From leather material: one may apply water without rubbing, or one may gently rub off the dirt without using water.

c. From cloth materials: one can remove the solid part (chunk) on top, but the liquid stain, which absorbed (stuck) into the material, must remain. Therefore, applying water or any other cleaning liquid is Chayav, since this will clean both parts.

However, part of the absorbed stain may be removed if:

(1) It is removed with a change -- e.g. by flicking one's fingers on the other side of the material, and

(2) A spot is left behind.

4. Absorbent and still wet (liquids such as wine, juice, soda, dirty water).

a. This can be removed in any manner from glass or plastic material. Example: One may clean eyeglasses by first putting water and then wiping it away.

b. A water-resistant raincoat may be shaken out only lightly.

c. One cannot clean the liquid by wringing, squeezing, or shaking cloth materials.

Consequently, one may not even touch or move a soaking wet cloth, as it is certain that water will be squeezed out in the process.

It is also prohibited to squeeze or wring out water that is "suspended" between particles, as opposed to absorbed. Example: squeezing water out of a [synthetic] toothbrush.

Gezeirot:

1. Soiling a material in a way that one might be tempted to clean that material afterwards. Therefore, it is prohibited to wipe muddy hands with a clean towel. It is also advisable to avoid situations in which a material may get dirty. Examples: when holding an infant on one's lap without an extra towel or diaper, or when placing one's hat on a public coat rack where it may fall on the ground.

2. Using absorbent materials to soak up [dirty] liquids, because one might come to squeeze out the liquid (an act of cleaning). This only applies to materials that one does not want to become wet. It is permitted, however, to dry dishes with a [special] dish towel even if the towel will get wet, since it is designed to get wet. However, it is still prohibited to squeeze out the towel, or to use it when it becomes soaking wet.

Because of the concern for wringing out materials, it is customary not to take showers on Shabbat. In a case of great discomfort, one may take a cold shower, provided that the drying towel is large, and care is taken not to squeeze one's hair.

Takanot:

1. One may not hang up a wet material specifically to dry, because of Mahris Ayin (others might think it is permitted to do laundry on Shabbat). One may hang wet laundry on its hook (i.e. where it is normally hung when dry), but not in a "drying place" (e.g. on the wash line).

Laundry hung on Erev Shabbat may be left there during Shabbat (though it may disturb your neighbor's Shabbat atmosphere), and can even be taken down on Shabbat -- provided it is needed for use on Shabbat, and that it was not soaking wet at the beginning of Shabbat (because it would then be Muktzah).

2. In instances where cleaning a material is permitted, it is still prohibited to scrub very strongly because of a prohibition against excessive exertion on Shabbat. Example: cleaning a tabletop or dishes of a difficult stain.