Hello
I’m new to the Forum and I will be introducing myself soon. 
I’m interested to know if members know about an ancient technique used to blacken armour in the Renaissance period that involved using COW HORN ? I have heard about the use of cow horn to give armour a deep black protective finish effective against rust from several sources and I’m wondering if the technique really existed in the past and is it still used today by blacksmiths ? If you know anything about the cow horn technique then I would be very interested to read you.
I have asked modern day armourers about the use of cow horn but know one so far has heard of it . What modern armourers generally use is boiled linseed oil sometimes mixed with soot. I don’t know if this is an historically correct technique for blackening armour but it seems to be the one that all modern makes of reproduction armour use.
If you know of any other techniques to give steel a deep black finish then I am interested too.
Thanks in advance !