are the beautifully decorated silk
wrestlers wear on special occasions, such as the dohyoiri
(the ring entering ceremony) during a basho
(a sumo tournament). 化粧
(ke-shou) is cosmetic
The heavy, embroidered keshomawasi is unique to each wrestler. It will bear his shikona - his ring-name - and the name of the person or company who has donated it. It will be hand made (by men, not women), and can cost between 400.000 and 500.000 yen. Bulgarian Komusubi Kotooshu's keshomawashi is sponsored by Meiji Dairies, a corporation that produces "Bulgarian Yogurt", and Ozeki Chiyotaikai is sponsored by a Canadian company, which explains the large red maple leaf on his red and white keshomawashi (before that, Chiyotaikai had a Coca Cola-sponsored keshomawashi).
The tradition of the decorated keshomawashi is not as old as all that. It was founded around 1900 when the Japanese newspaper, the "Mainichi Shimbun", began offering a decorative keshomawashi as an award to the sumotori (sumo wrestler) who won a tournament. (There would be 9 or 11 bouts in a tournament. The current 15 day tournaments were introduced in 1939, and became the standard in 1949). The sumotori who came out of the tournament with the fewest losses was declared the winner. If two wrestlers ended up tied, the wrestler with the highest rank won the prize.
Today, the keshomawashi will typically be presented to the wrestler when he reaches juryo, the second highest division in sumo. It will be sponsored by either a company (it's a great way to advertise, since sumo is broadcast nationwide), or by the heya, the wrestler's school or stable. Keshomawashi are usually presented during the March tournament: Haru Basho (March is the traditional month in which to enter sumo). The presentation of the newly promoted wrestlers in their brand new keshomawashi takes place on Nakabi, the 8th day of the tournament.
Sources: sumoforum.net/glossary.html#, faroutliers.blogspot.com/2004_11_01_faroutliers_archive.html and sumo.or.jp/eng
Check out a lot of beautiful keshomawashi on http://www.wada-mitsumasa.com/gallery/keshoumawashi/