Sounds a bit long. Need it for a site job where the ironmongery is already fitted!Brass has lots of copper and I've patinised copper. Do you have any spare for trials?
For copper you paint on either vinegar or salt water or both. One tends to green, the other blue. Get a dish, I use an old margarine tub or similar, put in some ammonia, some household cleaners are ammonia based, I have a litre bottle from a French supermarket so haven't bought any for years. You just need a small amount. Don't immerse, lay the object over the top balanced on pencils or something and cover loosely with plastic bag or clingfilm. Keep an eye on it, one of my copper trials changed colour in 10 mins, but you might need more. Rinse off.
Works for copper, should for brass and if it doesn't its only cost you a splash of vinegar and a pinch of salt plus ammonia which is useful for all sorts. It might work without the ammonia bit, just cover so it stays wet, but it will take lots longer.
I wonder if fuming over ammonia alone would darken it without the patination?
Worth a go.
I can imagine ! Think I'll stick to the patination fluid. On a serious note you probably ought to lacquer them, otherwise handling will quickly remove the colour.Sorry to introduce a note of crudity here, but I have always just suspended brass items (replacement harpsichord hinges, etc.) over a dish of urine for a couple of weeks. Female urine works best, but gaining co-operation can be complicated.