|Brass Necklace with Wood and Magnesite|
Even though brass itself does not contain nickel, that does not prevent me from asking questions, and as always, being slightly suspicious. There are times when the "machinability" of brass has been "improved" by the addition of lead. This is much less true with modern brass, though it is perfectly worthwhile to ask (and only buy) if brass is lead-free.
Also there is a quirk I have learned about only as I have started asking more questions - sometimes the antiquing process itself can introduce trace amounts of nickel to the surface of the brass. This happens in the factory where the metal used as antique plating may be introduced to contaminants from other metals, that may in fact contain nickel. If this were to happen, it would be in only trace amounts, however it would be on the surface of the brass, and not acceptable for those with allergies.
If brass has been oxidized either naturally or chemically, it is fine to use. Some antique plating is also okay. I buy only supplies that are guaranteed and/or labeled by the supplier as nickel and lead free. My suppliers already know that I can be rather persistent, and sometimes I repeat my questions just to be sure I get the same answer. I hope they understand. I'm doing it for you.