White steel is the purest of the carbon steels. The ingredients are mostly just iron and carbon. Shirogami #1 has slightly more carbon than the more common Shirogami #2, which allows it to get even harder.
Shirogami is among the easiest of steels to sharpen and is capable of achieving the most perfect mirror finished edge. This steel can be forged to incredible hardness, which translates to exceptional edge retention. Why do you think knife and sword makers love this steel?
Special care must be taken with carbon knives as they are reactive and prone to rust. Make sure to wipe off the blade regularly during use as well as wash and dry it thoroughly when you're done. However, after a nice strong patina has formed on the blade they are less likely to rust. Patina is your friend!