Cynanide process vs bone charcoal process and durability

[BRDHNTR]

What is the difference between these two processes for case coloring? And is one process more durable than the other. About 10 yrs ago, i had DelGregos re case color and restock my late grandfathers 16 ga vh. The stock was worn out totally as were the original colors on this 1920's vintage VH. DelGregos used the cynanide process. I had to return it for some corrective work that i need not go into. But suffice to say that the colors on the base plate and sides have lost much of their colors from minimal handling and no use of cleaning solvents. Im having Bachelders re case it with their bone charcoal process. A vhe that Brad recased for me and one that i shoot weekly has held its colors extremely well. Others in this forum are well educated and experienced with tbese 2 processes and i would be interested in hearing their views on same. Thanking all in advance. Oh, this 16 ga vh goes to my oldest grandson when im dust.