Finish for flexible leather (belts, etc.)

[Dan D'Silva]

Hello again.  The aforementioned Achaemenid reenactor in California is asking me about a weapon belt that's dyed red.  I told him this was achievable if he wanted one made of veg-tan (something I'm not convinced was used early in the period, but that's another question entirely) but that the brush-on dyes I'm used to using tend to bleed onto clothing unless sealed.

So I'd like to know if there's a period-appropriate sealant.  I've experimented with beeswax, but it seems like if it's melted into the surface for a good bond, the leather turns white whenever it flexes and the color can only be restored by heating it until the wax melts again.   Am I applying it wrong, or do I need to use a different material?

Thank you.