(If you do not have access to birch bark, cereal box cardboard works pretty good!)
Birch bark is the preferred material because of its natural ‘tack’ – which has a nice drag on a knife to keep the sheath from sliding off. This is the traditional sheath material of Scandinavia. However, most folk do not have access to bark of the paper birch, so the hard cardboard of cereal boxes makes a fine substitute, I just put the gray color outside. To adjust the tightness of this type of sheath…either push an object into it – like a ball point pen or pencil to loosen it – or squeezing edgeways also to loosens it’s grip. To tighten the grip bend it sideways. Whatever you do, please do not go cutting a band of bark off of a birch tree, even in the middle of the forest – nothing is uglier, and with the decline of birches – they don’t need to be at more risk of disease. I have even made plenty of fine birch bark sheaths out of bark off of dead trees or firewood. Ideally, you know of a logger who will mark the trees he will be taking ahead of time, and, come mid June you can go to those trees and cut off the bark. When it is ‘ripe’ it will practically blow off the tree once you make knife cuts. Good luck!
Cut with knife and straight edge, scissors, paper cutter, whatever…
Cut length of strip to about 5x blade length and 2x width
Peel bark in half
Fold, crease folds
Trim like this
insert strip of bark (3/16 to 3/8 width) like this ,on an angle so it can be spiraled up the sheath
When wrapping around pull tightly and crease folds
Like this, make it tight
Continue wrapping and inserting like this, pushing each wrap down tightly against the one before, you can insert a drop of glue under lace before last insertion, but it really is rarely necessary. Trim and you are done.
Finished. Be sure when inserting or withdrawing a knife blade to always put a little pressure against the back of the blade to avoid cutting the sheath with the edge. This particular sheath has wide bands, but a much narrower wrapping is attractive and gives a fine appearance.