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Looking for advice on making a irekozaya for a chef's knife saya?


William W

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I got my hands on some beautiful dried oak logs.  Figured I'd try to make a saya out of the thinner boards I made out of em, which lead to me learning about the different properties you want in a saya's wood.  I'd still like to use the oak though, so figured I'd use an inner liner.  The purpose of this is for a white steel #2 knife.  Based largely on this forum I'm looking for some poplar, magnolia, alder, or basswood for the inside.  But that begs the question, how thick does the interior need to be? And, since a kitchen knife saya is much thinner than a normal one, do I need to worry about the tannic acid of the oak leaching through the inner wood? Also, for the finish, is it like a cutting board where you just give it as much oil as it'll take, or do you go light with it to prevent swelling?

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Personally, I'd glue them together with hide glue. That has been shown to prevent oxidation of the metal. I have a sword I hilted with oak, but used hide glue to glue the inner core. It seems to effectively seal the wood. Maybe there's other sealers you can use as an adhesive, but I'm unaware of which ones. You can probably get away with a pretty thin inner layer of poplar or basswood. The grain is pretty tight and the wood pretty soft. My experience is that alder is basically the same thing as poplar at some places, at least it's hard for me to tell them apart (I got one board of each, can't tell the difference). Magnolia is basically impossible to find anywhere locally, at least for me. Poplar/alder seem to be a great choice in my experience.

 

There's no need to finish the wood for a saya for a kitchen knife. If you must, a small amount of a neutral oil such as mineral oil would be enough. You can use a lacquer, urushi was used on some saya, but almost every storage saya (shirasaya) I've ever seen for a Japanese knife or sword has been unfinished. They typically finish the wood using knives, chisels or planes though, typically not sanded. 

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I'd go with a thin layer of basswood, it's even less porous than poplar and, if you do use hide glue to join the lining to the oak (not to mention the main seams!), should stop most of the rust potential.  Outside finish is up to you. Like Carlos said, if you want traditional it'll be a white featureless wood with no finish, but I've seen them made from various woods.  Nothing too fancy, but I've seen some shiny Wenge saya that looked good.  Your call, in other words.  The mekugi should be a contrasting color to the saya for best effect, though.  Like, black buffalo horn or bog oak for a basswood or poplar saya, white bone or bamboo for Wenge, that sort of thing.  

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On 11/27/2023 at 1:12 PM, Carlos Lara said:

Personally, I'd glue them together with hide glue. That has been shown to prevent oxidation of the metal. I have a sword I hilted with oak, but used hide glue to glue the inner core. It seems to effectively seal the wood. Maybe there's other sealers you can use as an adhesive, but I'm unaware of which ones. You can probably get away with a pretty thin inner layer of poplar or basswood. The grain is pretty tight and the wood pretty soft. My experience is that alder is basically the same thing as poplar at some places, at least it's hard for me to tell them apart (I got one board of each, can't tell the difference). Magnolia is basically impossible to find anywhere locally, at least for me. Poplar/alder seem to be a great choice in my experience.

 

There's no need to finish the wood for a saya for a kitchen knife. If you must, a small amount of a neutral oil such as mineral oil would be enough. You can use a lacquer, urushi was used on some saya, but almost every storage saya (shirasaya) I've ever seen for a Japanese knife or sword has been unfinished. They typically finish the wood using knives, chisels or planes though, typically not sanded. 

Thanks for all the info, I assumed that it would be best to fill the wood with a nonreactive material to "dilute" anything acidic already in the wood.  Also didn't even think about the fact that of course you should use a non reactive glue.  Having done some Googling, hide glues probably the best, but I am curious about sokui.  I know it's weaker, but do you have any experience with it?

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Yes, sukui is a great glue for wood, and is pretty easy to use, but I wouldn't expect it to seal as well as hide glue. Hide glue is a dense gel of proteins that cures pretty hard, and is pretty impermeable, but sokui is just starch glue, like wallpaper paste. It holds way better than I thought it would, but I wouldn't use it for that. The Japanese use hide glue for various things, like gluing on a kurikata, fuchi or kashira. It's probably stronger than sokui, but not as mild if the blade is going to touch it.

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