I've had a bit of experience also with Bois Darc. Just finished a fixed blade for my grandad. I have used both superglue and a mixture of boiled linseed oil, mineral spirits and bees wax (I got the bees wax idea from Darrel Ralph; Thanks Darrel!). Both types of finishes are great...just depends whether you want a more gloss or matte finish on the handle. I understand that the bees wax slows or even halts the oxidation process. Thus, the handle will not darken as fast with age. The linseed oil mixture darkens the finish just a bit, but still very nice looking. The only problem that I have experienced is when I polish the neighboring bolster. The rouge compound I use to polish the bolster/guard will leave an awful looking black mess on the wood so I usually mask the wood with masking tape and then get after the bolster/guard. Perhaps this is true with other woods as well, but it seems especially troublesome with Boid Darc. Anyway, it turns out great in the end with care. Any black mess from the polishing compound appears to be easily removed using common alcohol.
Cheers,
>> DeWayne <<