Yakisugi/Shou Sugi Ban

Hi,
Does anyone know if oil was originally used in Japan to seal Yakisugi siding?

I'm building a pallet cabin....plan to finish the siding with this burnt-wood technique.
I'm going for the "alligator" look, ie deeply charred and not brushed......It would save some money if I didn't have to seal it with oil.

Any knowledge most welcome.

Update on pallet cabin. I love Yakisugi! The deeper the burn, the longer it lasts.

Wow, Cath I am just looking at your cabin. Mind sharing how it is a few years down the road? And when you say "the deeper the burn...", may I ask approximately how deep? Thanks so much.