A Shirasaya is simply a case intended for storing a blade when not in use. Made of a single peice of Honok that has been cut to shape,cut in two and chiseled out to fit the blade. This is then glued together with rice glue and the final shape is applied using traditional Japanese planes and can be either oval or octagonal.
The term Koshirae refers to a scabbard and handle complete with fittings (fuchi kashira etc.) usually with a braided handle and with a lacquered saya. They can range from very simple to excessively elaborate in design. For a Sayashi the work that goes into koshirae is a complex and sometimes difficult process as he/she must take into account the other elements that will need to follow to complete the job.
When planing a new koshirae several factors need to be taken into account such as style of koshirae, available fittings, materials etc. Once the fittings have been acquired a koshirae shitaji is created, this is basically the wood core shaped and fitted with all its furniture ( fuchi, kashira, horn etc) .
This is a difficult process as everything must line up correctly and a smooth transition from Tsuka to Saya is required. Next the Samekawa is applied (Same Gise) in either a full wrap or panels which is predetermined before work commences. Generally but not strictly speaking I do the Lacquering next followed by the Tsukamaki although this is subject to other variables.
Koshirae can take anywhere from 1 to 12 months to complete depending on design and work load.