Alternatives to Black Nickel finish on Brass?

We manufacture two types of round threaded parts from brass - both approx. 0.5" diameter. One part is approx. 1.5" long, the other is approx. 1.25" long; both have "through holes which are threaded.

Quantities are 10 - 15 k of each style. (together, 20k - 30k per year)

We need a good (and low cost) black finish. We are currently using Black nickel, but are disatisfied with the inconsistency of the color -- cosmetics are very important for this application.

(1) Is there some sort of "varnish" or "lacquer" commonly used in the finishing industry that the plater can apply over top of the black nickel? How do I find vendors with this capability? Also . . .

(2) Are there other types of finishing processes that I should consider (e.g. black anodizing, black chrome, etc.) NOTE: in addition to cosmetics, low cost is very important too.

There are two types of Black nickel plating. One is sulphate based while the other one is Chloride based.

I feel that chloride base solution or salt gives better results in terms of color consistancy.